{"id":1727,"date":"2017-10-10T16:00:17","date_gmt":"2017-10-10T16:00:17","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/?post_type=chapter&#038;p=1727"},"modified":"2018-10-05T19:39:57","modified_gmt":"2018-10-05T19:39:57","slug":"spin-spin-splitting-in-proton-nmr","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/chapter\/spin-spin-splitting-in-proton-nmr\/","title":{"raw":"Spin-Spin Splitting in Proton NMR","rendered":"Spin-Spin Splitting in Proton NMR"},"content":{"raw":"<div class=\"elm-header\">\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Objectives<\/h3>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div id=\"skills\">\r\n\r\nAfter completing this section, you should be able to\r\n<ol>\r\n \t<li>explain the spin-spin splitting pattern observed in the <sup>1<\/sup>H NMR spectrum of a simple organic compound, such as chloroethane or 2-bromopropane.<\/li>\r\n \t<li>interpret the splitting pattern of a given <sup>1<\/sup>H NMR spectrum.<\/li>\r\n \t<li>determine the structure of a relatively simple organic compound, given its <sup>1<\/sup>H NMR spectrum and other relevant information.<\/li>\r\n \t<li>use coupling constants to determine which groups of protons are coupling with one another in a <sup>1<\/sup>H NMR spectrum.<\/li>\r\n \t<li>predict the splitting pattern which should be observed in the <sup>1<\/sup>H NMR spectrum of a given organic compound.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div id=\"note\">\r\n<div class=\"textbox key-takeaways\">\r\n<h3 class=\"elm-header\">Key Terms<\/h3>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div>\r\n\r\nMake certain that you can define, and use in context, the key terms below.\r\n<ul>\r\n \t<li>coupling constant<\/li>\r\n \t<li>multiplet<\/li>\r\n \t<li>quartet<\/li>\r\n \t<li>triplet<\/li>\r\n \t<li>doublet<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox\">\r\n<h3>Study Notes<\/h3>\r\nFrom what we have learned about <sup>1<\/sup>H NMR spectra so far, we might predict that the spectrum of 1,1,2-trichloroethane, CHCl<sub>2<\/sub>CH<sub>2<\/sub>Cl, would consist of two peaks\u2014one, at about 2.5-4.0 <em>\u03b4<\/em>, expected for CH<sub>2<\/sub>-halogen compounds and one shifted downfield because of the presence of \u00a0an additional electronegative chlorine atom on the second carbon. However, when we look at the spectrum it appears to be much more complex. True, we see absorptions in the regions we predicted, but these absorptions appear as a group of two peaks (a <em>doublet<\/em>) and a group of three peaks (a <em>triplet<\/em>). This complication, which may be disturbing to a student who longs for the simple life, is in fact very useful to the organic chemist, and adds greatly to the power of NMR spectroscopy as a tool for the elucidation of chemical structures. The split peaks (<em>multiplets<\/em>) arise because the magnetic field experienced by the protons of one group is influenced by the spin arrangements of the protons in an adjacent group.\r\n\r\nSpin-spin coupling is often one of the more challenging topics for organic chemistry students to master. Remember the <em>n<\/em> + 1 rule and the associated coupling patterns.\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_1\">\r\n<h3 class=\"editable\">The source of spin-spin coupling<\/h3>\r\nThe <sup>1<\/sup>H-NMR spectra that we have seen so far (of methyl acetate and <em>para<\/em>-xylene) are somewhat unusual in the sense that in both of these molecules, each set of protons generates a single NMR signal.\u00a0 In fact, the <sup>1<\/sup>H-NMR spectra of most organic\u00a0 molecules contain proton signals that are 'split' into two or more sub-peaks.\u00a0 Rather than being a complication, however, this splitting behavior actually provides us with more information about our sample molecule.\r\n\r\nConsider the spectrum for 1,1,2-trichloroethane.\u00a0 In this and in many spectra to follow, we show enlargements of individual signals so that the signal splitting patterns are recognizable.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154337\/image058.png\" alt=\"image058.png\" width=\"682px\" height=\"363px\" \/>\r\n\r\nThe signal at 3.96 ppm, corresponding to the two H<sub>a<\/sub> protons, is split into two subpeaks of equal height (and area) \u2013 this is referred to as a <strong>doublet<\/strong>.\u00a0 The H<sub>b<\/sub> signal at 5.76 ppm, on the other hand, is split into three sub-peaks, with the middle peak higher than the two outside peaks - if we were to integrate each subpeak, we would see that the area under the middle peak is twice that of each of the outside peaks.\u00a0 This is called a <strong>triplet<\/strong>.\r\n\r\nThe source of signal splitting is a phenomenon called <strong>spin-spin coupling<\/strong>, a term that describes the magnetic interactions between neighboring, non-equivalent NMR-active nuclei. In our 1,1,2 trichloromethane example, the H<sub>a<\/sub> and H<sub>b<\/sub> protons are spin-coupled to each other. Here's how it works, looking first at the H<sub>a<\/sub> signal: in addition to being shielded by nearby valence electrons, each of the H<sub>a<\/sub> protons is also influenced by the small magnetic field generated by H<sub>b<\/sub> next door (remember, each spinning proton is like a tiny magnet). The magnetic moment of H<sub>b<\/sub> will be aligned <em>with<\/em> B<sub>0<\/sub> in (slightly more than) half of the molecules in the sample, while in the remaining half of the molecules it will be opposed to B<sub>0<\/sub>.\u00a0 The B<sub>eff<\/sub> \u2018felt\u2019 by H<sub>a<\/sub> is a slightly weaker if H<sub>b<\/sub> is aligned against B<sub>0<\/sub>, or slightly stronger if H<sub>b<\/sub> is aligned with B<sub>0<\/sub>.\u00a0 In other words, in half of the molecules H<sub>a<\/sub> is <em>shielded<\/em> by H<sub>b<\/sub> (thus the NMR signal is shifted slightly upfield) and in the other half H<sub>a<\/sub> is <em>deshielded<\/em> by H<sub>b<\/sub>(and the NMR signal shifted slightly downfield).\u00a0 What would otherwise be a single H<sub>a<\/sub> peak has been split into two sub-peaks (a doublet), one upfield and one downfield of the original signal.\u00a0 These ideas an be illustrated by a <strong>splitting diagram<\/strong>, as shown below.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154340\/image060.png\" alt=\"image060.png\" width=\"581px\" height=\"309px\" \/>\r\n\r\nNow, let's think about the H<sub>b<\/sub>signal.\u00a0 The magnetic environment experienced by H<sub>b<\/sub> is influenced by the fields of both neighboring H<sub>a<\/sub> protons, which we will call H<sub>a1<\/sub> and H<sub>a2<\/sub>.\u00a0 There are four possibilities here, each of which is equally probable.\u00a0 First, the magnetic fields of both H<sub>a1<\/sub> and H<sub>a2<\/sub> could be aligned with B<sub>0<\/sub>, which would deshield H<sub>b<\/sub>, shifting its NMR signal slightly downfield.\u00a0 Second, both the H<sub>a1<\/sub> and H<sub>a2<\/sub> magnetic fields could be aligned opposed to B<sub>0<\/sub>, which would shield H<sub>b<\/sub>, shifting its resonance signal slightly upfield.\u00a0 Third and fourth, H<sub>a1<\/sub> could be with B<sub>0<\/sub> and H<sub>a2<\/sub> opposed, or H<sub>a1<\/sub>opposed to B<sub>0<\/sub> and H<sub>a2<\/sub> with B<sub>0<\/sub>.\u00a0 In each of the last two cases, the shielding effect of one H<sub>a<\/sub> proton would cancel the deshielding effect of the other, and the chemical shift of H<sub>b<\/sub> would be unchanged.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154343\/image062.png\" alt=\"image062.png\" width=\"543px\" height=\"360px\" \/>\r\n\r\nSo in the end, the signal for H<sub>b<\/sub> is a <strong>triplet<\/strong>, with the middle peak twice as large as the two outer peaks because there are <em>two<\/em> ways that H<sub>a1<\/sub> and H<sub>a2<\/sub> can cancel each other out.\r\n\r\nNow, consider the spectrum for ethyl acetate:\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154345\/image064.png\" alt=\"image064.png\" width=\"713px\" height=\"363px\" \/>\r\n\r\nWe see an unsplit <strong>'singlet'<\/strong> peak at 1.833 ppm that corresponds to the acetyl (H<sub>a<\/sub>) hydrogens \u2013 this is similar to the signal for the acetate hydrogens in methyl acetate that we considered earlier.\u00a0 This signal is unsplit because there are no adjacent hydrogens on the molecule.\u00a0 The signal at 1.055 ppm for the H<sub>c<\/sub> hydrogens is split into a triplet by the two H<sub>b<\/sub> hydrogens next door.\u00a0 The explanation here is the same as the explanation for the triplet peak we saw previously for 1,1,2-trichloroethane.\r\n\r\nThe H<sub>b<\/sub>hydrogens give rise to a <strong>quartet <\/strong>signal at 3.915 ppm \u2013 notice that the two middle peaks are taller then the two outside peaks.\u00a0 This splitting pattern results from the spin-coupling effect of the <em>three<\/em> H<sub>c<\/sub> hydrogens next door, and can be explained by an analysis similar to that which we used to explain the doublet and triplet patterns.\r\n<div>\r\n<div id=\"example\">\r\n<div class=\"textbox examples\">\r\n<h3>Example<\/h3>\r\n<ol start=\"1\">\r\n \t<li>Explain, using left and right arrows to illustrate the possible combinations of\u00a0 nuclear spin states for the H<sub>c<\/sub> hydrogens, why the H<sub>b<\/sub> signal in ethyl acetate is split into a quartet.<\/li>\r\n \t<li>The integration ratio of doublets is 1:1, and of triplets is 1:2:1. What is the integration ratio of the H<sub>b<\/sub> quartet in ethyl acetate? (Hint \u2013 use the illustration that you drew in part a to answer this question.)<\/li>\r\n<\/ol>\r\n<h3>Solutions<\/h3>\r\n[reveal-answer q=\"430140\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"430140\"]\r\n\r\na)\r\n<p align=\"center\"><img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/6474\/image267.png?revision=1\" alt=\"image266.png\" width=\"183\" height=\"187\" \/><\/p>\r\nb)\u00a0 The figure above demonstrates that the quartet subpeaks integrate to 1:3:3:1 (eg., there are three ways for two spins to be aligned with B<sub>0<\/sub>\u00a0and one against B<sub>0<\/sub>).\u00a0 As an analogy, if you flip three coins at once, you have a 1 in eight chance of getting all heads, 1 in 8 chance of all tails, a 3 in 8 chance of two heads and a tail, and a 3 in 8 chance of two tails and a head.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\nBy now, you probably have recognized the pattern which is usually referred to as the <strong><em>n<\/em> + 1 rule<\/strong>: if a set of hydrogens has <em>n<\/em> neighboring, non-equivalent hydrogens, it will be split into <em>n<\/em> + 1 subpeaks. Thus the two H<sub>b<\/sub> hydrogens in ethyl acetate split the H<sub>c<\/sub> signal into a triplet, and the three H<sub>c<\/sub> hydrogens split the H<sub>b<\/sub> signal into a quartet.\u00a0 This is very useful information if we are trying to determine the structure of an unknown molecule: if we see a triplet signal, we know that the corresponding hydrogen or set of hydrogens has two `neighbors`.\u00a0 When we begin to determine structures of unknown compounds using <sup>1<\/sup>H-NMR spectral data, it will become more apparent how this kind of information can be used.\r\n\r\nThree important points need to be emphasized here.\u00a0 First, signal splitting only occurs between non-equivalent hydrogens \u2013 in other words, H<sub>a1<\/sub> in 1,1,2-trichloroethane is <em>not<\/em> split by H<sub>a2<\/sub>, and vice-versa.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154348\/image066.png\" alt=\"image066.png\" width=\"293px\" height=\"123px\" \/>\r\n\r\nSecond, splitting occurs primarily between hydrogens that are separated by three bonds.\u00a0 This is why the H<sub>a<\/sub> hydrogens in ethyl acetate form a singlet\u2013 the nearest hydrogen neighbors are five bonds away, too far for coupling to occur.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154350\/image068.png\" alt=\"image068.png\" width=\"432px\" height=\"98px\" \/>\r\n\r\nOccasionally we will see four-bond and even 5-bond splitting, but in these cases the magnetic influence of one set of hydrogens on the other set is much more subtle than what we typically see in three-bond splitting (more details about how we quantify coupling interactions is provided in section 5.5B). Finally, splitting is most noticeable with hydrogens bonded to carbon.\u00a0 Hydrogens that are bonded to heteroatoms (alcohol or amino hydrogens, for example) are coupled weakly - or not at all - to their neighbors.\u00a0 This has to do with the fact that these protons exchange rapidly with solvent or other sample molecules.\r\n\r\nBelow are a few more examples of chemical shift and splitting pattern information for some relatively simple organic molecules.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154352\/image070.png\" alt=\"image070.png\" width=\"634px\" height=\"193px\" \/>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154355\/image072.png\" alt=\"image072.png\" width=\"574\" height=\"211\" \/>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154357\/image074.png\" alt=\"image074.png\" width=\"202\" height=\"95\" \/>\r\n\r\n<\/div>\r\n<div id=\"section_2\">\r\n<h3 class=\"editable\"><span class=\"title mt-title-edit\">Multiplicity in Proton NMR<\/span><\/h3>\r\n<p dir=\"LTR\">The number of lines in a peak is always one more (n+1) than the number of hydrogens on the neighboring carbon.\u00a0 This table summarizes coupling patterns that arise when protons have different numbers of neighbors.<\/p>\r\n\r\n<table dir=\"ltr\" style=\"border-spacing: 2px\" border=\"\" cellpadding=\"12\">\r\n<tbody>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\"># of lines<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">ratio of lines<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">term for peak<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\"># of neighbors<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">-<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">singlet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">0<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">2<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">doublet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">3<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:2:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">triplet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">2<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">4<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:3:3:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">quartet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">3<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">5<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:4:6:4:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">quintet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">4<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">6<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:5:10:10:5:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">sextet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">5<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">7<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:6:15:20:15:6:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">septet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">6<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">8<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:7:21:35:35:21:7:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">octet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">7<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>\r\n<p dir=\"LTR\">9<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">1:8:28:56:70:56:28:8:1<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">nonet<\/p>\r\n<\/td>\r\n<td>\r\n<p dir=\"LTR\">8<\/p>\r\n<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<div>\r\n<div class=\"textbox examples\">\r\n<h3>Example<\/h3>\r\n<div id=\"section_2\">\r\n\r\nHow many proton signals would you expect to see in the <sup>1<\/sup>H-NMR spectrum of triclosan (a common antimicrobial agent found in detergents)? For each of the proton signals, predict the splitting pattern. Assume that you see only 3-bond coupling.\r\n<h3>Solution<\/h3>\r\n[reveal-answer q=\"656290\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"656290\"]\r\n\r\nBecause of the symmetry in the molecule, there are only four proton signals.\u00a0 Predicted splitting is indicated.\r\n<p align=\"center\"><img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/6476\/image269.png?revision=1\" alt=\"image268.png\" width=\"231\" height=\"184\" \/>[\/hidden-answer]<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div class=\"textbox examples\">\r\n<div id=\"section_2\">\r\n<h3 class=\"boxtitle\">Example<\/h3>\r\nPredict the splitting pattern for the <sup>1<\/sup>H-NMR signals corresponding to the protons at the locations indicated by arrows (the structure is that of the neurotransmitter serotonin).\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154359\/image076.png\" alt=\"image076.png\" width=\"218px\" height=\"151px\" \/>\r\n<h3>Solution<\/h3>\r\n[reveal-answer q=\"194579\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"194579\"]\r\n<p align=\"center\"><img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/6478\/image271.png?revision=1\" alt=\"image270.png\" width=\"181\" height=\"151\" \/><\/p>\r\n(recall that splitting is generally not seen with protons on heteroatoms)\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_3\">\r\n<h3 class=\"editable\">Coupling constants<\/h3>\r\nChemists quantify the spin-spin coupling effect using something called the <strong>coupling constant<\/strong>, which is abbreviated with the capital letter <em>J<\/em>.\u00a0 The coupling constant is simply the difference, expressed in Hz, between two adjacent sub-peaks in a split signal.\u00a0 For our doublet in the 1,1,2-trichloroethane spectrum, for example, the two subpeaks are separated by 6.1 Hz, and thus we write <sup>3<\/sup><em>J<\/em><sub>a-b<\/sub> = 6.1 Hz.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154402\/image078.png\" alt=\"image078.png\" width=\"471px\" height=\"281px\" \/>\r\n\r\nThe superscript 3 tells us that this is a three-bond coupling interaction, and the a-b subscript tells us that we are talking about coupling between H<sub>a<\/sub> and H<sub>b<\/sub>. Unlike the chemical shift value, <em>the coupling constant, expressed in Hz, is the same regardless of the applied field strength of the NMR magnet<\/em>.\u00a0 This is because the strength of the magnetic moment of a neighboring proton, which is the source of the spin-spin coupling phenomenon, does <em>not<\/em> depend on the applied field strength.\r\n\r\nWhen we look closely at the triplet signal in 1,1,2-trichloroethane, we see that the coupling constant - the `gap` between subpeaks - is 6.1 Hz, the same as for the doublet. This is an important concept!\u00a0 The coupling constant <sup>3<\/sup>J<sub>a-b<\/sub> quantifies the magnetic interaction between the H<sub>a<\/sub> and H<sub>b<\/sub> hydrogen sets, and <em>this interaction is of the same magnitude in either direction<\/em>. In other words, H<sub>a<\/sub> influences H<sub>b<\/sub> to the same extent that H<sub>b<\/sub> influences H<sub>a<\/sub>. When looking at more complex NMR spectra, this idea of <strong>reciprocal coupling constants<\/strong> can be very helpful in identifying the coupling relationships between proton sets.\r\n\r\nCoupling constants between proton sets on neighboring sp<sup>3<\/sup>-hybridized carbons is typically in the region of 6-8 Hz.\u00a0 With protons bound to sp<sup>2<\/sup>-hybridized carbons, coupling constants can range from 0 Hz (no coupling at all) to 18 Hz, depending on the bonding arrangement.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154404\/image080.png\" alt=\"image080.png\" width=\"607px\" height=\"114px\" \/>\r\n\r\nFor vinylic hydrogens in a <em>trans<\/em> configuration, we see coupling constants in the range of <sup>3<\/sup>J = 11-18 Hz, while <em>cis<\/em> hydrogens couple in the <sup>3<\/sup>J = 6-15 Hz range. The 2-bond coupling between hydrogens bound to the same alkene carbon (referred to as geminal hydrogens) is very fine, generally 5 Hz or lower.\u00a0 <em>Ortho<\/em> hydrogens on a benzene ring couple at 6-10 Hz, while 4-bond coupling of up to 4 Hz is sometimes seen between <em>meta<\/em> hydrogens.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154406\/image082.png\" alt=\"image082.png\" width=\"420px\" height=\"145px\" \/>\r\n\r\nFine (2-3 Hz) coupling is often seen between an aldehyde proton and a three-bond neighbor. <a title=\"Organic Chemistry\/Organic Chemistry With a Biological Emphasis\/Reference Tables\/Typical coupling constants in NMR\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\/Reference_Tables\/Typical_coupling_constants_in_NMR\" rel=\"internal\">Table 4<\/a> lists typical constant values.\r\n\r\n<\/div>\r\n<div id=\"section_4\">\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<strong>Note:<\/strong> Remember, chemically equivalent protons do not couple with one another to give spin-spin splitting.\r\n<div id=\"s61718\">\r\n<div id=\"section_32\">\r\n<h4 id=\"Questions-61718\">Questions<\/h4>\r\n<strong>1.<\/strong>Predict the splitting patterns of the following molecules:\r\n\r\n<img class=\"internal default\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154408\/13-11-1qu.png\" alt=\"\" width=\"591\" height=\"79\" \/>\r\n\r\n<b>2.\u00a0<\/b>\r\n\r\nDraw the following according to the criteria given.\r\n\r\nA. C<sub>3<\/sub>H<sub>5<\/sub>O; two triplet, 1 doublet\r\n\r\nB. C<sub>4<\/sub>H<sub>8<\/sub>O<sub>2<\/sub>; three singlets\r\n\r\nC. C<sub>5<\/sub>H<sub>12<\/sub>; one singlet\r\n\r\n<b>3.\u00a0<\/b>\r\n\r\nThe following spectrum is for C<sub>3<\/sub>H<sub>8<\/sub>O. Determine the structure.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154412\/13.113.gif\" alt=\"\" width=\"519\" height=\"380\" \/>\r\n\r\nA triplet; B singlet; C sextet; D triplet\r\n\r\n[reveal-answer q=\"853894\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"853894\"]\r\n<h3 id=\"Solutions-61718\">Solutions<\/h3>\r\n<strong>1.<\/strong>\r\n\r\nA.\u00a0H: Doublet.\u00a0H: Septet\r\n\r\nB.\u00a0H: Doublet,\u00a0H: Triplet\r\n\r\nC.\u00a0H: Singlet,\u00a0H: Quartet,\u00a0H: Triplet<img class=\"size-medium wp-image-1899 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/10155736\/13.111-300x192.png\" alt=\"\" width=\"300\" height=\"192\" \/>\r\n\r\n<strong>2.\u00a0<\/strong>\r\n\r\n<img class=\"size-medium wp-image-1900 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/10155904\/13.1121-300x161.png\" alt=\"\" width=\"300\" height=\"161\" \/>These are just some drawings, more may be possible.\r\n\r\n<strong>3.\u00a0<\/strong>\r\n\r\n<img class=\"size-medium wp-image-1901 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/10155952\/13.113a1-300x164.png\" alt=\"\" width=\"300\" height=\"164\" \/>\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"s61718\">\r\n<div id=\"section_32\">\r\n\r\nSource: SDBSWeb :\u00a0<a class=\"external\" title=\"http:\/\/sdbs.db.aist.go.jp\" href=\"http:\/\/sdbs.db.aist.go.jp\/\" target=\"_blank\" rel=\"external nofollow noopener\">http:\/\/sdbs.db.aist.go.jp<\/a>\u00a0(National Institute of Advanced Industrial Science and Technology, 3 December 2016)\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_5\">\r\n<h3 class=\"editable\">Contributors<\/h3>\r\n<ul>\r\n \t<li><a class=\"external\" title=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" href=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" target=\"_blank\" rel=\"external nofollow noopener\">Dr. Dietmar Kennepohl<\/a> FCIC (Professor of Chemistry, <a class=\"external\" title=\"http:\/\/www.athabascau.ca\/\" href=\"http:\/\/www.athabascau.ca\/\" target=\"_blank\" rel=\"external nofollow noopener\">Athabasca University<\/a>)<\/li>\r\n \t<li>Prof. Steven Farmer (<a class=\"external\" title=\"http:\/\/www.sonoma.edu\" href=\"http:\/\/www.sonoma.edu\" target=\"_blank\" rel=\"external nofollow noopener\">Sonoma State University<\/a>)<\/li>\r\n \t<li><a title=\"Organic_Chemistry_With_a_Biological_Emphasis\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\" rel=\"internal\">Organic Chemistry With a Biological Emphasis <\/a>by\u00a0<a class=\"external\" title=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" href=\"http:\/\/facultypages.morris.umn.edu\/%7Esoderbt\/\" target=\"_blank\" rel=\"external nofollow noopener\">Tim Soderberg<\/a>\u00a0(University of Minnesota, Morris)<\/li>\r\n \t<li><a href=\"http:\/\/employees.csbsju.edu\/cschaller\/srobi.htm\" rel=\"cc:attributionURL\">Chris P Schaller, Ph.D.<\/a>, <a class=\"external\" title=\"http:\/\/www.csbsju.edu\/Chemistry.htm\" href=\"http:\/\/www.csbsju.edu\/Chemistry.htm\" target=\"_blank\" rel=\"external nofollow noopener\">(College of Saint Benedict \/ Saint John's University)<\/a><\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"elm-header\">\n<div class=\"textbox learning-objectives\">\n<h3>Objectives<\/h3>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div id=\"skills\">\n<p>After completing this section, you should be able to<\/p>\n<ol>\n<li>explain the spin-spin splitting pattern observed in the <sup>1<\/sup>H NMR spectrum of a simple organic compound, such as chloroethane or 2-bromopropane.<\/li>\n<li>interpret the splitting pattern of a given <sup>1<\/sup>H NMR spectrum.<\/li>\n<li>determine the structure of a relatively simple organic compound, given its <sup>1<\/sup>H NMR spectrum and other relevant information.<\/li>\n<li>use coupling constants to determine which groups of protons are coupling with one another in a <sup>1<\/sup>H NMR spectrum.<\/li>\n<li>predict the splitting pattern which should be observed in the <sup>1<\/sup>H NMR spectrum of a given organic compound.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div id=\"note\">\n<div class=\"textbox key-takeaways\">\n<h3 class=\"elm-header\">Key Terms<\/h3>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div>\n<p>Make certain that you can define, and use in context, the key terms below.<\/p>\n<ul>\n<li>coupling constant<\/li>\n<li>multiplet<\/li>\n<li>quartet<\/li>\n<li>triplet<\/li>\n<li>doublet<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox\">\n<h3>Study Notes<\/h3>\n<p>From what we have learned about <sup>1<\/sup>H NMR spectra so far, we might predict that the spectrum of 1,1,2-trichloroethane, CHCl<sub>2<\/sub>CH<sub>2<\/sub>Cl, would consist of two peaks\u2014one, at about 2.5-4.0 <em>\u03b4<\/em>, expected for CH<sub>2<\/sub>-halogen compounds and one shifted downfield because of the presence of \u00a0an additional electronegative chlorine atom on the second carbon. However, when we look at the spectrum it appears to be much more complex. True, we see absorptions in the regions we predicted, but these absorptions appear as a group of two peaks (a <em>doublet<\/em>) and a group of three peaks (a <em>triplet<\/em>). This complication, which may be disturbing to a student who longs for the simple life, is in fact very useful to the organic chemist, and adds greatly to the power of NMR spectroscopy as a tool for the elucidation of chemical structures. The split peaks (<em>multiplets<\/em>) arise because the magnetic field experienced by the protons of one group is influenced by the spin arrangements of the protons in an adjacent group.<\/p>\n<p>Spin-spin coupling is often one of the more challenging topics for organic chemistry students to master. Remember the <em>n<\/em> + 1 rule and the associated coupling patterns.<\/p>\n<\/div>\n<\/div>\n<div id=\"section_1\">\n<h3 class=\"editable\">The source of spin-spin coupling<\/h3>\n<p>The <sup>1<\/sup>H-NMR spectra that we have seen so far (of methyl acetate and <em>para<\/em>-xylene) are somewhat unusual in the sense that in both of these molecules, each set of protons generates a single NMR signal.\u00a0 In fact, the <sup>1<\/sup>H-NMR spectra of most organic\u00a0 molecules contain proton signals that are &#8216;split&#8217; into two or more sub-peaks.\u00a0 Rather than being a complication, however, this splitting behavior actually provides us with more information about our sample molecule.<\/p>\n<p>Consider the spectrum for 1,1,2-trichloroethane.\u00a0 In this and in many spectra to follow, we show enlargements of individual signals so that the signal splitting patterns are recognizable.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154337\/image058.png\" alt=\"image058.png\" width=\"682px\" height=\"363px\" \/><\/p>\n<p>The signal at 3.96 ppm, corresponding to the two H<sub>a<\/sub> protons, is split into two subpeaks of equal height (and area) \u2013 this is referred to as a <strong>doublet<\/strong>.\u00a0 The H<sub>b<\/sub> signal at 5.76 ppm, on the other hand, is split into three sub-peaks, with the middle peak higher than the two outside peaks &#8211; if we were to integrate each subpeak, we would see that the area under the middle peak is twice that of each of the outside peaks.\u00a0 This is called a <strong>triplet<\/strong>.<\/p>\n<p>The source of signal splitting is a phenomenon called <strong>spin-spin coupling<\/strong>, a term that describes the magnetic interactions between neighboring, non-equivalent NMR-active nuclei. In our 1,1,2 trichloromethane example, the H<sub>a<\/sub> and H<sub>b<\/sub> protons are spin-coupled to each other. Here&#8217;s how it works, looking first at the H<sub>a<\/sub> signal: in addition to being shielded by nearby valence electrons, each of the H<sub>a<\/sub> protons is also influenced by the small magnetic field generated by H<sub>b<\/sub> next door (remember, each spinning proton is like a tiny magnet). The magnetic moment of H<sub>b<\/sub> will be aligned <em>with<\/em> B<sub>0<\/sub> in (slightly more than) half of the molecules in the sample, while in the remaining half of the molecules it will be opposed to B<sub>0<\/sub>.\u00a0 The B<sub>eff<\/sub> \u2018felt\u2019 by H<sub>a<\/sub> is a slightly weaker if H<sub>b<\/sub> is aligned against B<sub>0<\/sub>, or slightly stronger if H<sub>b<\/sub> is aligned with B<sub>0<\/sub>.\u00a0 In other words, in half of the molecules H<sub>a<\/sub> is <em>shielded<\/em> by H<sub>b<\/sub> (thus the NMR signal is shifted slightly upfield) and in the other half H<sub>a<\/sub> is <em>deshielded<\/em> by H<sub>b<\/sub>(and the NMR signal shifted slightly downfield).\u00a0 What would otherwise be a single H<sub>a<\/sub> peak has been split into two sub-peaks (a doublet), one upfield and one downfield of the original signal.\u00a0 These ideas an be illustrated by a <strong>splitting diagram<\/strong>, as shown below.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154340\/image060.png\" alt=\"image060.png\" width=\"581px\" height=\"309px\" \/><\/p>\n<p>Now, let&#8217;s think about the H<sub>b<\/sub>signal.\u00a0 The magnetic environment experienced by H<sub>b<\/sub> is influenced by the fields of both neighboring H<sub>a<\/sub> protons, which we will call H<sub>a1<\/sub> and H<sub>a2<\/sub>.\u00a0 There are four possibilities here, each of which is equally probable.\u00a0 First, the magnetic fields of both H<sub>a1<\/sub> and H<sub>a2<\/sub> could be aligned with B<sub>0<\/sub>, which would deshield H<sub>b<\/sub>, shifting its NMR signal slightly downfield.\u00a0 Second, both the H<sub>a1<\/sub> and H<sub>a2<\/sub> magnetic fields could be aligned opposed to B<sub>0<\/sub>, which would shield H<sub>b<\/sub>, shifting its resonance signal slightly upfield.\u00a0 Third and fourth, H<sub>a1<\/sub> could be with B<sub>0<\/sub> and H<sub>a2<\/sub> opposed, or H<sub>a1<\/sub>opposed to B<sub>0<\/sub> and H<sub>a2<\/sub> with B<sub>0<\/sub>.\u00a0 In each of the last two cases, the shielding effect of one H<sub>a<\/sub> proton would cancel the deshielding effect of the other, and the chemical shift of H<sub>b<\/sub> would be unchanged.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154343\/image062.png\" alt=\"image062.png\" width=\"543px\" height=\"360px\" \/><\/p>\n<p>So in the end, the signal for H<sub>b<\/sub> is a <strong>triplet<\/strong>, with the middle peak twice as large as the two outer peaks because there are <em>two<\/em> ways that H<sub>a1<\/sub> and H<sub>a2<\/sub> can cancel each other out.<\/p>\n<p>Now, consider the spectrum for ethyl acetate:<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154345\/image064.png\" alt=\"image064.png\" width=\"713px\" height=\"363px\" \/><\/p>\n<p>We see an unsplit <strong>&#8216;singlet&#8217;<\/strong> peak at 1.833 ppm that corresponds to the acetyl (H<sub>a<\/sub>) hydrogens \u2013 this is similar to the signal for the acetate hydrogens in methyl acetate that we considered earlier.\u00a0 This signal is unsplit because there are no adjacent hydrogens on the molecule.\u00a0 The signal at 1.055 ppm for the H<sub>c<\/sub> hydrogens is split into a triplet by the two H<sub>b<\/sub> hydrogens next door.\u00a0 The explanation here is the same as the explanation for the triplet peak we saw previously for 1,1,2-trichloroethane.<\/p>\n<p>The H<sub>b<\/sub>hydrogens give rise to a <strong>quartet <\/strong>signal at 3.915 ppm \u2013 notice that the two middle peaks are taller then the two outside peaks.\u00a0 This splitting pattern results from the spin-coupling effect of the <em>three<\/em> H<sub>c<\/sub> hydrogens next door, and can be explained by an analysis similar to that which we used to explain the doublet and triplet patterns.<\/p>\n<div>\n<div id=\"example\">\n<div class=\"textbox examples\">\n<h3>Example<\/h3>\n<ol start=\"1\">\n<li>Explain, using left and right arrows to illustrate the possible combinations of\u00a0 nuclear spin states for the H<sub>c<\/sub> hydrogens, why the H<sub>b<\/sub> signal in ethyl acetate is split into a quartet.<\/li>\n<li>The integration ratio of doublets is 1:1, and of triplets is 1:2:1. What is the integration ratio of the H<sub>b<\/sub> quartet in ethyl acetate? (Hint \u2013 use the illustration that you drew in part a to answer this question.)<\/li>\n<\/ol>\n<h3>Solutions<\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q430140\">Show Answer<\/span><\/p>\n<div id=\"q430140\" class=\"hidden-answer\" style=\"display: none\">\n<p>a)<\/p>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/6474\/image267.png?revision=1\" alt=\"image266.png\" width=\"183\" height=\"187\" \/><\/p>\n<p>b)\u00a0 The figure above demonstrates that the quartet subpeaks integrate to 1:3:3:1 (eg., there are three ways for two spins to be aligned with B<sub>0<\/sub>\u00a0and one against B<sub>0<\/sub>).\u00a0 As an analogy, if you flip three coins at once, you have a 1 in eight chance of getting all heads, 1 in 8 chance of all tails, a 3 in 8 chance of two heads and a tail, and a 3 in 8 chance of two tails and a head.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>By now, you probably have recognized the pattern which is usually referred to as the <strong><em>n<\/em> + 1 rule<\/strong>: if a set of hydrogens has <em>n<\/em> neighboring, non-equivalent hydrogens, it will be split into <em>n<\/em> + 1 subpeaks. Thus the two H<sub>b<\/sub> hydrogens in ethyl acetate split the H<sub>c<\/sub> signal into a triplet, and the three H<sub>c<\/sub> hydrogens split the H<sub>b<\/sub> signal into a quartet.\u00a0 This is very useful information if we are trying to determine the structure of an unknown molecule: if we see a triplet signal, we know that the corresponding hydrogen or set of hydrogens has two `neighbors`.\u00a0 When we begin to determine structures of unknown compounds using <sup>1<\/sup>H-NMR spectral data, it will become more apparent how this kind of information can be used.<\/p>\n<p>Three important points need to be emphasized here.\u00a0 First, signal splitting only occurs between non-equivalent hydrogens \u2013 in other words, H<sub>a1<\/sub> in 1,1,2-trichloroethane is <em>not<\/em> split by H<sub>a2<\/sub>, and vice-versa.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154348\/image066.png\" alt=\"image066.png\" width=\"293px\" height=\"123px\" \/><\/p>\n<p>Second, splitting occurs primarily between hydrogens that are separated by three bonds.\u00a0 This is why the H<sub>a<\/sub> hydrogens in ethyl acetate form a singlet\u2013 the nearest hydrogen neighbors are five bonds away, too far for coupling to occur.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154350\/image068.png\" alt=\"image068.png\" width=\"432px\" height=\"98px\" \/><\/p>\n<p>Occasionally we will see four-bond and even 5-bond splitting, but in these cases the magnetic influence of one set of hydrogens on the other set is much more subtle than what we typically see in three-bond splitting (more details about how we quantify coupling interactions is provided in section 5.5B). Finally, splitting is most noticeable with hydrogens bonded to carbon.\u00a0 Hydrogens that are bonded to heteroatoms (alcohol or amino hydrogens, for example) are coupled weakly &#8211; or not at all &#8211; to their neighbors.\u00a0 This has to do with the fact that these protons exchange rapidly with solvent or other sample molecules.<\/p>\n<p>Below are a few more examples of chemical shift and splitting pattern information for some relatively simple organic molecules.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154352\/image070.png\" alt=\"image070.png\" width=\"634px\" height=\"193px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154355\/image072.png\" alt=\"image072.png\" width=\"574\" height=\"211\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154357\/image074.png\" alt=\"image074.png\" width=\"202\" height=\"95\" \/><\/p>\n<\/div>\n<div id=\"section_2\">\n<h3 class=\"editable\"><span class=\"title mt-title-edit\">Multiplicity in Proton NMR<\/span><\/h3>\n<p dir=\"LTR\">The number of lines in a peak is always one more (n+1) than the number of hydrogens on the neighboring carbon.\u00a0 This table summarizes coupling patterns that arise when protons have different numbers of neighbors.<\/p>\n<table dir=\"ltr\" style=\"border-spacing: 2px\" cellpadding=\"12\">\n<tbody>\n<tr>\n<td>\n<p dir=\"LTR\"># of lines<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">ratio of lines<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">term for peak<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\"># of neighbors<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">&#8211;<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">singlet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">0<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">2<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">doublet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">3<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:2:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">triplet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">2<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">4<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:3:3:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">quartet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">3<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">5<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:4:6:4:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">quintet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">4<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">6<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:5:10:10:5:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">sextet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">5<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">7<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:6:15:20:15:6:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">septet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">6<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">8<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:7:21:35:35:21:7:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">octet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">7<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p dir=\"LTR\">9<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">1:8:28:56:70:56:28:8:1<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">nonet<\/p>\n<\/td>\n<td>\n<p dir=\"LTR\">8<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div>\n<div class=\"textbox examples\">\n<h3>Example<\/h3>\n<div id=\"section_2\">\n<p>How many proton signals would you expect to see in the <sup>1<\/sup>H-NMR spectrum of triclosan (a common antimicrobial agent found in detergents)? For each of the proton signals, predict the splitting pattern. Assume that you see only 3-bond coupling.<\/p>\n<h3>Solution<\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q656290\">Show Answer<\/span><\/p>\n<div id=\"q656290\" class=\"hidden-answer\" style=\"display: none\">\n<p>Because of the symmetry in the molecule, there are only four proton signals.\u00a0 Predicted splitting is indicated.<\/p>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/6476\/image269.png?revision=1\" alt=\"image268.png\" width=\"231\" height=\"184\" \/><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div class=\"textbox examples\">\n<div id=\"section_2\">\n<h3 class=\"boxtitle\">Example<\/h3>\n<p>Predict the splitting pattern for the <sup>1<\/sup>H-NMR signals corresponding to the protons at the locations indicated by arrows (the structure is that of the neurotransmitter serotonin).<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154359\/image076.png\" alt=\"image076.png\" width=\"218px\" height=\"151px\" \/><\/p>\n<h3>Solution<\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q194579\">Show Answer<\/span><\/p>\n<div id=\"q194579\" class=\"hidden-answer\" style=\"display: none\">\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/6478\/image271.png?revision=1\" alt=\"image270.png\" width=\"181\" height=\"151\" \/><\/p>\n<p>(recall that splitting is generally not seen with protons on heteroatoms)<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_3\">\n<h3 class=\"editable\">Coupling constants<\/h3>\n<p>Chemists quantify the spin-spin coupling effect using something called the <strong>coupling constant<\/strong>, which is abbreviated with the capital letter <em>J<\/em>.\u00a0 The coupling constant is simply the difference, expressed in Hz, between two adjacent sub-peaks in a split signal.\u00a0 For our doublet in the 1,1,2-trichloroethane spectrum, for example, the two subpeaks are separated by 6.1 Hz, and thus we write <sup>3<\/sup><em>J<\/em><sub>a-b<\/sub> = 6.1 Hz.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154402\/image078.png\" alt=\"image078.png\" width=\"471px\" height=\"281px\" \/><\/p>\n<p>The superscript 3 tells us that this is a three-bond coupling interaction, and the a-b subscript tells us that we are talking about coupling between H<sub>a<\/sub> and H<sub>b<\/sub>. Unlike the chemical shift value, <em>the coupling constant, expressed in Hz, is the same regardless of the applied field strength of the NMR magnet<\/em>.\u00a0 This is because the strength of the magnetic moment of a neighboring proton, which is the source of the spin-spin coupling phenomenon, does <em>not<\/em> depend on the applied field strength.<\/p>\n<p>When we look closely at the triplet signal in 1,1,2-trichloroethane, we see that the coupling constant &#8211; the `gap` between subpeaks &#8211; is 6.1 Hz, the same as for the doublet. This is an important concept!\u00a0 The coupling constant <sup>3<\/sup>J<sub>a-b<\/sub> quantifies the magnetic interaction between the H<sub>a<\/sub> and H<sub>b<\/sub> hydrogen sets, and <em>this interaction is of the same magnitude in either direction<\/em>. In other words, H<sub>a<\/sub> influences H<sub>b<\/sub> to the same extent that H<sub>b<\/sub> influences H<sub>a<\/sub>. When looking at more complex NMR spectra, this idea of <strong>reciprocal coupling constants<\/strong> can be very helpful in identifying the coupling relationships between proton sets.<\/p>\n<p>Coupling constants between proton sets on neighboring sp<sup>3<\/sup>-hybridized carbons is typically in the region of 6-8 Hz.\u00a0 With protons bound to sp<sup>2<\/sup>-hybridized carbons, coupling constants can range from 0 Hz (no coupling at all) to 18 Hz, depending on the bonding arrangement.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154404\/image080.png\" alt=\"image080.png\" width=\"607px\" height=\"114px\" \/><\/p>\n<p>For vinylic hydrogens in a <em>trans<\/em> configuration, we see coupling constants in the range of <sup>3<\/sup>J = 11-18 Hz, while <em>cis<\/em> hydrogens couple in the <sup>3<\/sup>J = 6-15 Hz range. The 2-bond coupling between hydrogens bound to the same alkene carbon (referred to as geminal hydrogens) is very fine, generally 5 Hz or lower.\u00a0 <em>Ortho<\/em> hydrogens on a benzene ring couple at 6-10 Hz, while 4-bond coupling of up to 4 Hz is sometimes seen between <em>meta<\/em> hydrogens.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154406\/image082.png\" alt=\"image082.png\" width=\"420px\" height=\"145px\" \/><\/p>\n<p>Fine (2-3 Hz) coupling is often seen between an aldehyde proton and a three-bond neighbor. <a title=\"Organic Chemistry\/Organic Chemistry With a Biological Emphasis\/Reference Tables\/Typical coupling constants in NMR\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\/Reference_Tables\/Typical_coupling_constants_in_NMR\" rel=\"internal\">Table 4<\/a> lists typical constant values.<\/p>\n<\/div>\n<div id=\"section_4\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<p><strong>Note:<\/strong> Remember, chemically equivalent protons do not couple with one another to give spin-spin splitting.<\/p>\n<div id=\"s61718\">\n<div id=\"section_32\">\n<h4 id=\"Questions-61718\">Questions<\/h4>\n<p><strong>1.<\/strong>Predict the splitting patterns of the following molecules:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal default\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154408\/13-11-1qu.png\" alt=\"\" width=\"591\" height=\"79\" \/><\/p>\n<p><b>2.\u00a0<\/b><\/p>\n<p>Draw the following according to the criteria given.<\/p>\n<p>A. C<sub>3<\/sub>H<sub>5<\/sub>O; two triplet, 1 doublet<\/p>\n<p>B. C<sub>4<\/sub>H<sub>8<\/sub>O<sub>2<\/sub>; three singlets<\/p>\n<p>C. C<sub>5<\/sub>H<sub>12<\/sub>; one singlet<\/p>\n<p><b>3.\u00a0<\/b><\/p>\n<p>The following spectrum is for C<sub>3<\/sub>H<sub>8<\/sub>O. Determine the structure.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05154412\/13.113.gif\" alt=\"\" width=\"519\" height=\"380\" \/><\/p>\n<p>A triplet; B singlet; C sextet; D triplet<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q853894\">Show Answer<\/span><\/p>\n<div id=\"q853894\" class=\"hidden-answer\" style=\"display: none\">\n<h3 id=\"Solutions-61718\">Solutions<\/h3>\n<p><strong>1.<\/strong><\/p>\n<p>A.\u00a0H: Doublet.\u00a0H: Septet<\/p>\n<p>B.\u00a0H: Doublet,\u00a0H: Triplet<\/p>\n<p>C.\u00a0H: Singlet,\u00a0H: Quartet,\u00a0H: Triplet<img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-1899 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/10155736\/13.111-300x192.png\" alt=\"\" width=\"300\" height=\"192\" \/><\/p>\n<p><strong>2.\u00a0<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-1900 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/10155904\/13.1121-300x161.png\" alt=\"\" width=\"300\" height=\"161\" \/>These are just some drawings, more may be possible.<\/p>\n<p><strong>3.\u00a0<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-1901 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/10155952\/13.113a1-300x164.png\" alt=\"\" width=\"300\" height=\"164\" \/><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"s61718\">\n<div id=\"section_32\">\n<p>Source: SDBSWeb :\u00a0<a class=\"external\" title=\"http:\/\/sdbs.db.aist.go.jp\" href=\"http:\/\/sdbs.db.aist.go.jp\/\" target=\"_blank\" rel=\"external nofollow noopener\">http:\/\/sdbs.db.aist.go.jp<\/a>\u00a0(National Institute of Advanced Industrial Science and Technology, 3 December 2016)<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_5\">\n<h3 class=\"editable\">Contributors<\/h3>\n<ul>\n<li><a class=\"external\" title=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" href=\"http:\/\/science.athabascau.ca\/staff-pages\/dietmark\" target=\"_blank\" rel=\"external nofollow noopener\">Dr. Dietmar Kennepohl<\/a> FCIC (Professor of Chemistry, <a class=\"external\" title=\"http:\/\/www.athabascau.ca\/\" href=\"http:\/\/www.athabascau.ca\/\" target=\"_blank\" rel=\"external nofollow noopener\">Athabasca University<\/a>)<\/li>\n<li>Prof. Steven Farmer (<a class=\"external\" title=\"http:\/\/www.sonoma.edu\" href=\"http:\/\/www.sonoma.edu\" target=\"_blank\" rel=\"external nofollow noopener\">Sonoma State University<\/a>)<\/li>\n<li><a title=\"Organic_Chemistry_With_a_Biological_Emphasis\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\" rel=\"internal\">Organic Chemistry With a Biological Emphasis <\/a>by\u00a0<a class=\"external\" title=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" href=\"http:\/\/facultypages.morris.umn.edu\/%7Esoderbt\/\" target=\"_blank\" rel=\"external nofollow noopener\">Tim Soderberg<\/a>\u00a0(University of Minnesota, Morris)<\/li>\n<li><a href=\"http:\/\/employees.csbsju.edu\/cschaller\/srobi.htm\" rel=\"cc:attributionURL\">Chris P Schaller, Ph.D.<\/a>, <a class=\"external\" title=\"http:\/\/www.csbsju.edu\/Chemistry.htm\" href=\"http:\/\/www.csbsju.edu\/Chemistry.htm\" target=\"_blank\" rel=\"external nofollow noopener\">(College of Saint Benedict \/ Saint John&#8217;s University)<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":44985,"menu_order":11,"template":"","meta":{"_candela_citation":"[]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1727","chapter","type-chapter","status-publish","hentry"],"part":29,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1727","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/users\/44985"}],"version-history":[{"count":15,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1727\/revisions"}],"predecessor-version":[{"id":2353,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1727\/revisions\/2353"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/parts\/29"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1727\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/media?parent=1727"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=1727"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/contributor?post=1727"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/license?post=1727"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}