{"id":202,"date":"2018-11-21T18:18:50","date_gmt":"2018-11-21T18:18:50","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/?post_type=chapter&#038;p=202"},"modified":"2019-01-08T14:36:59","modified_gmt":"2019-01-08T14:36:59","slug":"13-2-conjugated-%cf%80-systems","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/chapter\/13-2-conjugated-%cf%80-systems\/","title":{"raw":"13.4. Conjugated \u03c0-systems","rendered":"13.4. Conjugated \u03c0-systems"},"content":{"raw":"<header class=\"elm-header\">\r\n<div class=\"elm-header-custom\">\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<article id=\"elm-main-content\" class=\"elm-content-container\"><section class=\"mt-content-container\">\r\n<div id=\"skills\">\r\n\r\nAfter completing this section, you should be able to\r\n<ol>\r\n \t<li>write a reaction sequence to show a convenient method for preparing a given conjugated diene from an alkene, allyl halide, alkyl dihalide or alcohol (diol).<\/li>\r\n \t<li>compare the stabilities of conjugated and nonconjugated dienes, using evidence obtained from hydrogenation experiments.<\/li>\r\n \t<li>discuss the bonding in a conjugated diene, such as 1,3-butadiene, in terms of the hybridization of the carbon atoms involved.<\/li>\r\n \t<li>discuss the bonding in 1,3-butadiene in terms of the molecular orbital theory, and draw a molecular orbital for this and similar compounds.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/section><\/article><\/div>\r\n<\/div>\r\n<\/header><article id=\"elm-main-content\" class=\"elm-content-container\"><section class=\"mt-content-container\">\r\n<div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3 class=\"boxtitle\">Key Terms<\/h3>\r\nMake certain that you can define, and use in context, the key terms below.\r\n<ul>\r\n \t<li>delocalized electrons<\/li>\r\n \t<li>node<span class=\"mt-font-size-16\"><span class=\"mt-font-arial\">Next, we'll consider the 1,3-butadiene molecule. From valence orbital theory alone we might expect that the C<sub>2<\/sub>-C<sub>3<\/sub> bond in this molecule, because it is a sigma bond, would be able to rotate freely. <\/span><\/span><\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<div id=\"note\">\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135051\/fig2-2-3.png\" alt=\"fig2-2-3.png\" width=\"204px\" height=\"179px\" \/>\r\n\r\n<span class=\"mt-font-arial\">Experimentally, however, it is observed that there is a significant barrier to rotation about the C<sub>2<\/sub>-C<sub>3<\/sub> bond, and that the entire molecule is planar. In addition, the C<sub>2<\/sub>-C<sub>3<\/sub> bond is 148 pm long, shorter than a typical carbon-carbon single bond (about 154 pm), though longer than a typical double bond (about 134 pm).<\/span>\r\n\r\n<span class=\"mt-font-arial\">Molecular orbital theory accounts for these observations with the concept of <strong>delocalized pi bonds<\/strong>. In this picture, the four <em>2p<\/em> atomic orbitals combine mathematically to form four pi molecular orbitals of increasing energy. Two of these - the bonding pi orbitals - are lower in energy than the <em>p<\/em> atomic orbitals from which they are formed, while two - the antibonding pi* orbitals - are higher in energy.<\/span>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135055\/fig2-2-4.png\" alt=\"fig2-2-4.png\" width=\"621px\" height=\"535px\" \/>\r\n\r\n<span class=\"mt-font-arial\">The lowest energy molecular orbital, pi<sub>1<\/sub>, has only constructive interaction and zero nodes. Higher in energy, but still lower than the isolated <em>p<\/em> orbitals, the pi<sub>2 <\/sub>orbital has one node but two constructive interactions - thus it is still a bonding orbital overall. Looking at the two antibonding orbitals, pi<sub>3<\/sub>* has two nodes and one constructive interaction, while pi<sub>4<\/sub>* has three nodes and zero constructive interactions. <\/span>\r\n\r\n<span class=\"mt-font-arial\">By the <em>aufbau<\/em> principle, the four electrons from the isolated 2<em>p<\/em><sub>z<\/sub> atomic orbitals are placed in the bonding pi<sub>1<\/sub> and pi<sub>2<\/sub> MO\u2019s. Because pi<sub>1<\/sub> includes constructive interaction between C<sub>2<\/sub> and C<sub>3<\/sub>, there is a degree, in the 1,3-butadiene molecule, of pi-bonding interaction between these two carbons, which accounts for its shorter length and the barrier to rotation. The valence bond picture of 1,3-butadiene shows the two pi bonds as being isolated from one another, with each pair of pi electrons \u2018stuck\u2019 in its own pi bond. However, molecular orbital theory predicts (accurately) that the four pi electrons are to some extent delocalized, or \u2018spread out\u2019, over the whole pi system.<\/span>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135058\/fig2-2-5.png\" alt=\"fig2-2-5.png\" width=\"408\" height=\"164\" \/>\r\n\r\n<span class=\"mt-font-arial\">1,3-butadiene is the simplest example of a system of <strong>conjugated pi<\/strong><strong> bonds<\/strong>. To be considered conjugated, two or more pi bonds must be separated by only one single bond \u2013 in other words, there cannot be an intervening <em>sp<sup>3<\/sup><\/em>-hybridized carbon, because this would break up the overlapping system of parallel <em>p<\/em> orbitals. In the compound below, for example, the C<sub>1<\/sub>-C<sub>2<\/sub> and C<sub>3<\/sub>-C<sub>4<\/sub> double bonds are conjugated, while the C<sub>6<\/sub>-C<sub>7<\/sub> double bond is <strong>isolated<\/strong> from the other two pi bonds by <em>sp<sup>3<\/sup><\/em>-hybridized C<sub>5<\/sub>. <\/span>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135100\/fig2-2-6.png\" alt=\"fig2-2-6.png\" width=\"256\" height=\"143\" \/>\r\n\r\n<span class=\"mt-font-arial\">A very important concept to keep in mind is that <em>there is an inherent thermodynamic stability associated with conjugation.<\/em> This stability can be measured experimentally by comparing the <strong>heat of hydrogenation<\/strong> of two different dienes. (Hydrogenation is a reaction type that we will learn much more about in chapter 15: essentially, it is the process of adding a hydrogen molecule - two protons and two electrons - to a p<\/span><span class=\"mt-font-times-new-roman\"><span class=\"mt-font-arial\"> bond). When the two <em>conjugated<\/em> double bonds of 1,3-pentadiene are 'hydrogenated' to produce pentane, about 225 kJ is released per mole of pentane formed. Compare that to the approximately 250 kJ\/mol released when the two <em>isolated<\/em> double bonds in 1,4-pentadiene are hydrogenated, also forming <\/span>pentane. <\/span>\r\n<p class=\"mt-align-justify\">The formation of synthetic polymers from dienes such as 1,3-butadiene and isoprene is discussed in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/chapter\/18-5-radical-polymerization-of-alkenes-polymers\/\">Section 18.5<\/a>. Synthetic polymers are large molecules made up of smaller repeating units. You are probably somewhat familiar with a number of these polymers; for example, polyethylene, polypropylene, polystyrene and poly(vinyl chloride).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"391\"]<img src=\"http:\/\/chem.libretexts.org\/@api\/deki\/files\/87117\/14-1b.png?origin=mt-web\" alt=\"energy diagram for the hydrogenation of 1,3-butadiene\" width=\"391\" height=\"331\" \/> Figure 13.6: Energy diagram for the hydrogenation of 1,3-butadiene (not to scale).[\/caption]\r\n<p class=\"mt-align-justify\">As the hydrogenation of 1,3-butadiene releases less than the predicted amount of energy, the energy content of 1,3-butadiene must be lower than we might have expected. In other words, 1,3-butadiene is more stable than its formula suggests.<\/p>\r\n<span class=\"mt-font-arial\">The conjugated diene is lower in energy: in other words, it is more stable. In general, conjugated pi bonds are more stable than isolated pi bonds.<\/span>\r\n\r\nHere is an energy diagram comparing different types of bonds with their heats of hydrogenation (per mole) to show relative stability of each molecule (1 kcal = 4.18 kJ).\u00a0 (The lower the heat of hydrogenation (per pi bond), the more stable the structure is.)\r\n\r\n<img class=\"internal aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1590\/energychart.bmp?revision=1#fixme\" alt=\"energychart.bmp\" width=\"613\" height=\"316\" \/>\r\n\r\nThe stabilization of dienes by conjugation is less dramatic than the aromatic stabilization of benzene. Nevertheless, similar resonance and molecular orbital descriptions of conjugation may be written.\r\n<div id=\"note\">\r\n<div class=\"textbox\">\r\n<div id=\"note\">\r\n<h3 class=\"boxtitle\">Synthesis of dienes<\/h3>\r\n<p class=\"mt-align-justify\">The two most frequent ways to synthesize conjugated dienes are dehydration of alcohols and dehydrohalogenation of organohalides, which were introduced in the preparation of alkenes (<a title=\"8.1 Preparation of Alkenes: A Preview of Elimination Reactions\" href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/9-9-applications-of-eliminations\/\" rel=\"internal\">Section 9.9<\/a>). The following scheme illustrates some of the routes to preparing a conjugated diene.<\/p>\r\n<p class=\"mt-align-justify\"><img class=\"aligncenter\" src=\"http:\/\/chem.libretexts.org\/@api\/deki\/files\/87116\/14-1a.png?origin=mt-web\" alt=\"various synthetic routes to 1,3-butadiene\" \/><\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span class=\"mt-font-arial\">Conjugated pi systems can involve oxygen and nitrogen atoms as well as carbon. In the metabolism of fat molecules, some of the key reactions involve alkenes that are conjugated to carbonyl groups. <\/span>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135105\/fig2-2-8.png\" alt=\"fig2-2-8.png\" width=\"159px\" height=\"76px\" \/>\r\n\r\n<span class=\"mt-font-size-16\"><span class=\"mt-font-arial\">MO theory is very useful in explaining why organic molecules that contain extended systems of conjugated pi bonds often have distinctive colors. <em>beta<\/em>-Carotene, the compound responsible for the orange color of carrots, has an extended system of 11 conjugated pi bonds.<\/span><\/span>\r\n\r\n&nbsp;\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135107\/fig2-2-9.png\" alt=\"fig2-2-9.png\" width=\"622px\" height=\"157px\" \/>\r\n\r\n&nbsp;\r\n<div>\r\n<div id=\"exercise\">\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<u><strong>Exercise 2.9:<\/strong><\/u><span class=\"mt-font-arial\"> Identify all conjugated and isolated double bonds in the structures below. For each conjugated pi system, specify the number of overlapping <em>p<\/em> orbitals, and how many pi electrons are shared among them.<\/span>\r\n\r\n&nbsp;\r\n\r\n<span class=\"mt-font-arial\"><img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135109\/figE2-2-1.png\" alt=\"figE2-2-1.png\" width=\"534px\" height=\"93px\" \/><\/span>\r\n\r\n<u><strong>Exercise 2.10: <\/strong><\/u><span class=\"mt-font-arial\">Identify all isolated and conjugated pi bonds in lycopene, the red-colored compound in tomatoes. How many pi electrons are contained in the conjugated pi system?<\/span>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135112\/figE2-2-2.png\" alt=\"figE2-2-2.png\" width=\"776px\" height=\"115px\" \/><a title=\"Solutions to Chapter 2 exercises\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II\/Solutions_to_Chapter_2_exercises\" target=\"_blank\" rel=\"internal noopener\">Solutions to exercises<\/a>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_1\" class=\"mt-section\">\r\n<div id=\"section_2\" class=\"mt-section\"><\/div>\r\n<\/div>\r\n<div id=\"section_6\" class=\"mt-section\"><\/div>\r\n<div id=\"section_7\" class=\"mt-section\">\r\n<div class=\"mt-contentreuse-widget\">\r\n<div id=\"s61719\" class=\"mt-include\">\r\n<div class=\"mt-section\">\r\n<h2>Reactions of dienes<\/h2>\r\n1,4-Addition is an electrophilic addition reaction of <a title=\"Conjugated Dienes\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Conjugation\/Conjugated_Dienes\" rel=\"internal\">conjugate dienes<\/a>.\r\n\r\neg: \u00a0Two electrophilic addition reactions could occur between 1,3-butadiene (1) and hydrogen chloride.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135713\/14addition1.png\" alt=\"14addition1.png\" width=\"600px\" height=\"369px\" \/>\r\n\r\nIn Reaction 1, the net reaction is addition of a hydrogen atom to C-1 and a chlorine atom to C-4 in 1. \u00a0Hence, Reaction 1 is called 1,4-addition and its product (2) 1,4-adduct.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135717\/14addition2.png\" alt=\"14addition2.png\" width=\"508\" height=\"180\" \/>\r\n\r\nIn Reaction 2, the net reaction is addition of a hydrogen atom to C-1 and a chlorine atom to C-2 in 1. Hence, Reaction 2 is called 1,2-addition and its product (3) 1,2-adduct.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135720\/14addition3.png\" alt=\"14addition3.png\" width=\"501\" height=\"181\" \/>\r\n\r\nThe regioselectivity of the overall reaction depends on the temperature. \u00a0At low temperature (eg: \u201378 \u00b0C), the major product is 3; at high temperature (\u0394), it is 2. \u00a0The carbon-carbon double bond in 2 is more highly substituted than the one in 3, so 2 is more stable than 3. \u00a0That the less stable 3 is the major product at low temperature implies that at low temperature the system is under kinetic control and 3 is the faster-forming product. That the more stable 2 is the major product at high temperature means the system is under thermodynamic control.\r\n<div id=\"section_1\" class=\"mt-section\">\r\n<h3 class=\"editable\">Mechanism at low temperature<\/h3>\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135723\/14addition4.png\" alt=\"14addition4.png\" width=\"508\" height=\"551\" \/>\r\n\r\nThe first step is reversible; the second step is irreversible. Thus, the overall reaction is irreversible, i.e, the system is under kinetic control and the major product is the faster-forming product. The first step, an acid-base reaction, generates the allylic carbocation 4 and the chloride ion. \u00a0In the second step, 4 reacts with the chloride ion. \u00a0In the two resonance forms (4a, 4b) of 4, 4a has the more stable <a title=\"Carbocation Rearrangements\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Reactions\/Elimination_Reactions\/E1_Reactions\/Carbocation_Rearrangements\" rel=\"internal\">carbocation <\/a>center and, therefore, is more stable than 4b. Thus, in the hybrid the partial positive charge on C-2 is more intense than that on C-4.\r\n\r\n<img class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135726\/14addition5.png\" alt=\"\" width=\"232\" height=\"89\" \/>\r\n\r\nIn the second step, the chloride ion reacts faster with the more electrophilic C-2, leading to 3. Thus, 3 is the faster-forming product and, since the system is under kinetic control, major product.\r\n\r\n<\/div>\r\n<div id=\"section_2\" class=\"mt-section\">\r\n<h3 class=\"editable\">Mechanism at high temperature<\/h3>\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135730\/14addition6.png\" alt=\"14addition6.png\" width=\"555\" height=\"602\" \/>\r\n\r\nNotice that, at high temperature, <strong>2<\/strong> and <strong>3<\/strong> interconvert via <strong>4<\/strong>.\r\n\r\n&nbsp;\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135733\/14addition7.png\" alt=\"14addition7.png\" width=\"600px\" height=\"151px\" \/>\r\n\r\nSince <strong>2<\/strong> is more stable than <strong>3<\/strong>, the equilibrium lies toward <strong>2<\/strong> and the equilibrium constant, K, is greater than <strong>1<\/strong>.\r\n\r\n<img class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135736\/14addition8.png\" alt=\"\" width=\"107\" height=\"179\" \/>\r\n\r\nHence, <strong>2<\/strong> is the major product.\r\n\r\n<\/div>\r\n<div id=\"section_3\" class=\"mt-section\">\r\n<h3 class=\"editable\">1,4-Addition, also known as conjugate addition, is a nucleophilic addition reaction of \u03b1, \u03b2\u2013unsaturated carbonyl compounds and \u03b1, \u03b2\u2013unsaturated nitriles.<\/h3>\r\neg: \u00a0Two nucleophilic addition reaction could occur between methylvinyl ketone (1) and methanethiol in basic medium.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135739\/14addition9.png\" alt=\"14addition9.png\" width=\"600px\" height=\"345px\" \/>\r\n\r\nmechanism of Reaction 1:\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135743\/14addition10.png\" alt=\"14addition10.png\" width=\"574\" height=\"460\" \/>\r\n\r\nThe net reaction from <strong>1<\/strong> to <strong>4<\/strong> is the addition of two ligands to atoms <em>1<\/em> and <em>4<\/em> in <strong>1<\/strong>. Hence, the reaction is called 1,4-addition, or conjugate addition, and its product (<strong>2<\/strong>) 1,4-adduct.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135746\/14addition11.png\" alt=\"14addition11.png\" width=\"600px\" height=\"175px\" \/>\r\n\r\nmechanism of Reaction 2:\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135750\/14addition12.png\" alt=\"14addition12.png\" width=\"557\" height=\"397\" \/>\r\n\r\nThe net reaction from <strong>1<\/strong> to <strong>3<\/strong> is the addition of two ligands to atoms <em>1<\/em> and <em>2<\/em> in <strong>1<\/strong>. \u00a0Hence, the reaction is called 1,2-addition, or direct addition, and the product (<strong>3<\/strong>) a 1,2-adduct.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135754\/14addition13.png\" alt=\"14addition13.png\" width=\"600px\" height=\"162px\" \/>\r\n\r\nThe overall reaction between an \u03b1, \u03b2\u2013unsaturated compound and a nucleophile is regioselective. Whether the dominant process is 1,4-addition or 1,2-addition depends on several factors, such as the alkene-containing reactant (the \u03b1, \u03b2\u2013unsaturated compound), nucleophile, solvent, concentration, temperature, reaction time, and catalyst, if any, making if difficult to make a generalization. Most resonance-stabilized carbon nucleophiles, such as enolate ions and enamines overwhelmingly prefer 1,4-addition to 1,2-addition. (See <a title=\"Michael Addition\" href=\"https:\/\/chem.libretexts.org\/Ancillary_Materials\/Reference\/Organic_Chemistry_Glossary\/Michael_Addition\" rel=\"internal\">Michael addition<\/a>)\r\n\r\nhttps:\/\/youtu.be\/r1LFkcKM6nA\r\n<h3><img class=\"alignnone wp-image-2839 size-thumbnail\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/07161339\/frame-6-150x150.png\" alt=\"\" width=\"150\" height=\"150\" \/><\/h3>\r\n<h3 class=\"editable\">Contributors<\/h3>\r\n<ul>\r\n \t<li><a title=\"http:\/\/chemwiki.ucdavis.edu\/Organic_Chemistry\/Organic_Chemistry_With_a_Biological_Emphasis\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\" rel=\"internal\"><strong>Organic Chemistry With a Biological Emphasis\u00a0<\/strong><\/a>by\u00a0<a class=\"external\" title=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" href=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" target=\"_blank\" rel=\"external nofollow noopener\">Tim Soderberg<\/a>\u00a0(University of Minnesota, Morris)<\/li>\r\n \t<li><a class=\"external\" title=\"http:\/\/www.uvu.edu\/profpages\/profiles\/show\/user_id\/1776\" href=\"http:\/\/www.uvu.edu\/profpages\/profiles\/show\/user_id\/1776\" target=\"_blank\" rel=\"external nofollow noopener\"><span class=\"gD\">Gamini Gunawardena<\/span><\/a>\u00a0from the\u00a0<a class=\"external\" title=\"http:\/\/science.uvu.edu\/ochem\/\" href=\"http:\/\/science.uvu.edu\/ochem\/\" target=\"_blank\" rel=\"external nofollow noopener\">OChemPal\u00a0<\/a>site (<a class=\"external\" title=\"http:\/\/www.uvu.edu\/chemistry\/\" href=\"http:\/\/www.uvu.edu\/chemistry\/\" target=\"_blank\" rel=\"external nofollow noopener\">Utah Valley University<\/a>)<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/section><\/article>","rendered":"<header class=\"elm-header\">\n<div class=\"elm-header-custom\">\n<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<article id=\"elm-main-content\" class=\"elm-content-container\">\n<section class=\"mt-content-container\">\n<div id=\"skills\">\n<p>After completing this section, you should be able to<\/p>\n<ol>\n<li>write a reaction sequence to show a convenient method for preparing a given conjugated diene from an alkene, allyl halide, alkyl dihalide or alcohol (diol).<\/li>\n<li>compare the stabilities of conjugated and nonconjugated dienes, using evidence obtained from hydrogenation experiments.<\/li>\n<li>discuss the bonding in a conjugated diene, such as 1,3-butadiene, in terms of the hybridization of the carbon atoms involved.<\/li>\n<li>discuss the bonding in 1,3-butadiene in terms of the molecular orbital theory, and draw a molecular orbital for this and similar compounds.<\/li>\n<\/ol>\n<\/div>\n<\/section>\n<\/article>\n<\/div>\n<\/div>\n<\/header>\n<article id=\"elm-main-content\" class=\"elm-content-container\">\n<section class=\"mt-content-container\">\n<div>\n<div class=\"textbox key-takeaways\">\n<h3 class=\"boxtitle\">Key Terms<\/h3>\n<p>Make certain that you can define, and use in context, the key terms below.<\/p>\n<ul>\n<li>delocalized electrons<\/li>\n<li>node<span class=\"mt-font-size-16\"><span class=\"mt-font-arial\">Next, we&#8217;ll consider the 1,3-butadiene molecule. From valence orbital theory alone we might expect that the C<sub>2<\/sub>-C<sub>3<\/sub> bond in this molecule, because it is a sigma bond, would be able to rotate freely. <\/span><\/span><\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div id=\"note\">\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135051\/fig2-2-3.png\" alt=\"fig2-2-3.png\" width=\"204px\" height=\"179px\" \/><\/p>\n<p><span class=\"mt-font-arial\">Experimentally, however, it is observed that there is a significant barrier to rotation about the C<sub>2<\/sub>-C<sub>3<\/sub> bond, and that the entire molecule is planar. In addition, the C<sub>2<\/sub>-C<sub>3<\/sub> bond is 148 pm long, shorter than a typical carbon-carbon single bond (about 154 pm), though longer than a typical double bond (about 134 pm).<\/span><\/p>\n<p><span class=\"mt-font-arial\">Molecular orbital theory accounts for these observations with the concept of <strong>delocalized pi bonds<\/strong>. In this picture, the four <em>2p<\/em> atomic orbitals combine mathematically to form four pi molecular orbitals of increasing energy. Two of these &#8211; the bonding pi orbitals &#8211; are lower in energy than the <em>p<\/em> atomic orbitals from which they are formed, while two &#8211; the antibonding pi* orbitals &#8211; are higher in energy.<\/span><\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135055\/fig2-2-4.png\" alt=\"fig2-2-4.png\" width=\"621px\" height=\"535px\" \/><\/p>\n<p><span class=\"mt-font-arial\">The lowest energy molecular orbital, pi<sub>1<\/sub>, has only constructive interaction and zero nodes. Higher in energy, but still lower than the isolated <em>p<\/em> orbitals, the pi<sub>2 <\/sub>orbital has one node but two constructive interactions &#8211; thus it is still a bonding orbital overall. Looking at the two antibonding orbitals, pi<sub>3<\/sub>* has two nodes and one constructive interaction, while pi<sub>4<\/sub>* has three nodes and zero constructive interactions. <\/span><\/p>\n<p><span class=\"mt-font-arial\">By the <em>aufbau<\/em> principle, the four electrons from the isolated 2<em>p<\/em><sub>z<\/sub> atomic orbitals are placed in the bonding pi<sub>1<\/sub> and pi<sub>2<\/sub> MO\u2019s. Because pi<sub>1<\/sub> includes constructive interaction between C<sub>2<\/sub> and C<sub>3<\/sub>, there is a degree, in the 1,3-butadiene molecule, of pi-bonding interaction between these two carbons, which accounts for its shorter length and the barrier to rotation. The valence bond picture of 1,3-butadiene shows the two pi bonds as being isolated from one another, with each pair of pi electrons \u2018stuck\u2019 in its own pi bond. However, molecular orbital theory predicts (accurately) that the four pi electrons are to some extent delocalized, or \u2018spread out\u2019, over the whole pi system.<\/span><\/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\/3773\/2018\/11\/21135058\/fig2-2-5.png\" alt=\"fig2-2-5.png\" width=\"408\" height=\"164\" \/><\/p>\n<p><span class=\"mt-font-arial\">1,3-butadiene is the simplest example of a system of <strong>conjugated pi<\/strong><strong> bonds<\/strong>. To be considered conjugated, two or more pi bonds must be separated by only one single bond \u2013 in other words, there cannot be an intervening <em>sp<sup>3<\/sup><\/em>-hybridized carbon, because this would break up the overlapping system of parallel <em>p<\/em> orbitals. In the compound below, for example, the C<sub>1<\/sub>-C<sub>2<\/sub> and C<sub>3<\/sub>-C<sub>4<\/sub> double bonds are conjugated, while the C<sub>6<\/sub>-C<sub>7<\/sub> double bond is <strong>isolated<\/strong> from the other two pi bonds by <em>sp<sup>3<\/sup><\/em>-hybridized C<sub>5<\/sub>. <\/span><\/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\/3773\/2018\/11\/21135100\/fig2-2-6.png\" alt=\"fig2-2-6.png\" width=\"256\" height=\"143\" \/><\/p>\n<p><span class=\"mt-font-arial\">A very important concept to keep in mind is that <em>there is an inherent thermodynamic stability associated with conjugation.<\/em> This stability can be measured experimentally by comparing the <strong>heat of hydrogenation<\/strong> of two different dienes. (Hydrogenation is a reaction type that we will learn much more about in chapter 15: essentially, it is the process of adding a hydrogen molecule &#8211; two protons and two electrons &#8211; to a p<\/span><span class=\"mt-font-times-new-roman\"><span class=\"mt-font-arial\"> bond). When the two <em>conjugated<\/em> double bonds of 1,3-pentadiene are &#8216;hydrogenated&#8217; to produce pentane, about 225 kJ is released per mole of pentane formed. Compare that to the approximately 250 kJ\/mol released when the two <em>isolated<\/em> double bonds in 1,4-pentadiene are hydrogenated, also forming <\/span>pentane. <\/span><\/p>\n<p class=\"mt-align-justify\">The formation of synthetic polymers from dienes such as 1,3-butadiene and isoprene is discussed in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/chapter\/18-5-radical-polymerization-of-alkenes-polymers\/\">Section 18.5<\/a>. Synthetic polymers are large molecules made up of smaller repeating units. You are probably somewhat familiar with a number of these polymers; for example, polyethylene, polypropylene, polystyrene and poly(vinyl chloride).<\/p>\n<div style=\"width: 401px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/chem.libretexts.org\/@api\/deki\/files\/87117\/14-1b.png?origin=mt-web\" alt=\"energy diagram for the hydrogenation of 1,3-butadiene\" width=\"391\" height=\"331\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 13.6: Energy diagram for the hydrogenation of 1,3-butadiene (not to scale).<\/p>\n<\/div>\n<p class=\"mt-align-justify\">As the hydrogenation of 1,3-butadiene releases less than the predicted amount of energy, the energy content of 1,3-butadiene must be lower than we might have expected. In other words, 1,3-butadiene is more stable than its formula suggests.<\/p>\n<p><span class=\"mt-font-arial\">The conjugated diene is lower in energy: in other words, it is more stable. In general, conjugated pi bonds are more stable than isolated pi bonds.<\/span><\/p>\n<p>Here is an energy diagram comparing different types of bonds with their heats of hydrogenation (per mole) to show relative stability of each molecule (1 kcal = 4.18 kJ).\u00a0 (The lower the heat of hydrogenation (per pi bond), the more stable the structure is.)<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1590\/energychart.bmp?revision=1#fixme\" alt=\"energychart.bmp\" width=\"613\" height=\"316\" \/><\/p>\n<p>The stabilization of dienes by conjugation is less dramatic than the aromatic stabilization of benzene. Nevertheless, similar resonance and molecular orbital descriptions of conjugation may be written.<\/p>\n<div id=\"note\">\n<div class=\"textbox\">\n<div id=\"note\">\n<h3 class=\"boxtitle\">Synthesis of dienes<\/h3>\n<p class=\"mt-align-justify\">The two most frequent ways to synthesize conjugated dienes are dehydration of alcohols and dehydrohalogenation of organohalides, which were introduced in the preparation of alkenes (<a title=\"8.1 Preparation of Alkenes: A Preview of Elimination Reactions\" href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/9-9-applications-of-eliminations\/\" rel=\"internal\">Section 9.9<\/a>). The following scheme illustrates some of the routes to preparing a conjugated diene.<\/p>\n<p class=\"mt-align-justify\"><img decoding=\"async\" class=\"aligncenter\" src=\"http:\/\/chem.libretexts.org\/@api\/deki\/files\/87116\/14-1a.png?origin=mt-web\" alt=\"various synthetic routes to 1,3-butadiene\" \/><\/p>\n<\/div>\n<\/div>\n<\/div>\n<p><span class=\"mt-font-arial\">Conjugated pi systems can involve oxygen and nitrogen atoms as well as carbon. In the metabolism of fat molecules, some of the key reactions involve alkenes that are conjugated to carbonyl groups. <\/span><\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135105\/fig2-2-8.png\" alt=\"fig2-2-8.png\" width=\"159px\" height=\"76px\" \/><\/p>\n<p><span class=\"mt-font-size-16\"><span class=\"mt-font-arial\">MO theory is very useful in explaining why organic molecules that contain extended systems of conjugated pi bonds often have distinctive colors. <em>beta<\/em>-Carotene, the compound responsible for the orange color of carrots, has an extended system of 11 conjugated pi bonds.<\/span><\/span><\/p>\n<p>&nbsp;<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135107\/fig2-2-9.png\" alt=\"fig2-2-9.png\" width=\"622px\" height=\"157px\" \/><\/p>\n<p>&nbsp;<\/p>\n<div>\n<div id=\"exercise\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<p><u><strong>Exercise 2.9:<\/strong><\/u><span class=\"mt-font-arial\"> Identify all conjugated and isolated double bonds in the structures below. For each conjugated pi system, specify the number of overlapping <em>p<\/em> orbitals, and how many pi electrons are shared among them.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p><span class=\"mt-font-arial\"><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135109\/figE2-2-1.png\" alt=\"figE2-2-1.png\" width=\"534px\" height=\"93px\" \/><\/span><\/p>\n<p><u><strong>Exercise 2.10: <\/strong><\/u><span class=\"mt-font-arial\">Identify all isolated and conjugated pi bonds in lycopene, the red-colored compound in tomatoes. How many pi electrons are contained in the conjugated pi system?<\/span><\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135112\/figE2-2-2.png\" alt=\"figE2-2-2.png\" width=\"776px\" height=\"115px\" \/><a title=\"Solutions to Chapter 2 exercises\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II\/Solutions_to_Chapter_2_exercises\" target=\"_blank\" rel=\"internal noopener\">Solutions to exercises<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_1\" class=\"mt-section\">\n<div id=\"section_2\" class=\"mt-section\"><\/div>\n<\/div>\n<div id=\"section_6\" class=\"mt-section\"><\/div>\n<div id=\"section_7\" class=\"mt-section\">\n<div class=\"mt-contentreuse-widget\">\n<div id=\"s61719\" class=\"mt-include\">\n<div class=\"mt-section\">\n<h2>Reactions of dienes<\/h2>\n<p>1,4-Addition is an electrophilic addition reaction of <a title=\"Conjugated Dienes\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Conjugation\/Conjugated_Dienes\" rel=\"internal\">conjugate dienes<\/a>.<\/p>\n<p>eg: \u00a0Two electrophilic addition reactions could occur between 1,3-butadiene (1) and hydrogen chloride.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135713\/14addition1.png\" alt=\"14addition1.png\" width=\"600px\" height=\"369px\" \/><\/p>\n<p>In Reaction 1, the net reaction is addition of a hydrogen atom to C-1 and a chlorine atom to C-4 in 1. \u00a0Hence, Reaction 1 is called 1,4-addition and its product (2) 1,4-adduct.<\/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\/3773\/2018\/11\/21135717\/14addition2.png\" alt=\"14addition2.png\" width=\"508\" height=\"180\" \/><\/p>\n<p>In Reaction 2, the net reaction is addition of a hydrogen atom to C-1 and a chlorine atom to C-2 in 1. Hence, Reaction 2 is called 1,2-addition and its product (3) 1,2-adduct.<\/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\/3773\/2018\/11\/21135720\/14addition3.png\" alt=\"14addition3.png\" width=\"501\" height=\"181\" \/><\/p>\n<p>The regioselectivity of the overall reaction depends on the temperature. \u00a0At low temperature (eg: \u201378 \u00b0C), the major product is 3; at high temperature (\u0394), it is 2. \u00a0The carbon-carbon double bond in 2 is more highly substituted than the one in 3, so 2 is more stable than 3. \u00a0That the less stable 3 is the major product at low temperature implies that at low temperature the system is under kinetic control and 3 is the faster-forming product. That the more stable 2 is the major product at high temperature means the system is under thermodynamic control.<\/p>\n<div id=\"section_1\" class=\"mt-section\">\n<h3 class=\"editable\">Mechanism at low temperature<\/h3>\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\/3773\/2018\/11\/21135723\/14addition4.png\" alt=\"14addition4.png\" width=\"508\" height=\"551\" \/><\/p>\n<p>The first step is reversible; the second step is irreversible. Thus, the overall reaction is irreversible, i.e, the system is under kinetic control and the major product is the faster-forming product. The first step, an acid-base reaction, generates the allylic carbocation 4 and the chloride ion. \u00a0In the second step, 4 reacts with the chloride ion. \u00a0In the two resonance forms (4a, 4b) of 4, 4a has the more stable <a title=\"Carbocation Rearrangements\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Reactions\/Elimination_Reactions\/E1_Reactions\/Carbocation_Rearrangements\" rel=\"internal\">carbocation <\/a>center and, therefore, is more stable than 4b. Thus, in the hybrid the partial positive charge on C-2 is more intense than that on C-4.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135726\/14addition5.png\" alt=\"\" width=\"232\" height=\"89\" \/><\/p>\n<p>In the second step, the chloride ion reacts faster with the more electrophilic C-2, leading to 3. Thus, 3 is the faster-forming product and, since the system is under kinetic control, major product.<\/p>\n<\/div>\n<div id=\"section_2\" class=\"mt-section\">\n<h3 class=\"editable\">Mechanism at high temperature<\/h3>\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\/3773\/2018\/11\/21135730\/14addition6.png\" alt=\"14addition6.png\" width=\"555\" height=\"602\" \/><\/p>\n<p>Notice that, at high temperature, <strong>2<\/strong> and <strong>3<\/strong> interconvert via <strong>4<\/strong>.<\/p>\n<p>&nbsp;<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135733\/14addition7.png\" alt=\"14addition7.png\" width=\"600px\" height=\"151px\" \/><\/p>\n<p>Since <strong>2<\/strong> is more stable than <strong>3<\/strong>, the equilibrium lies toward <strong>2<\/strong> and the equilibrium constant, K, is greater than <strong>1<\/strong>.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135736\/14addition8.png\" alt=\"\" width=\"107\" height=\"179\" \/><\/p>\n<p>Hence, <strong>2<\/strong> is the major product.<\/p>\n<\/div>\n<div id=\"section_3\" class=\"mt-section\">\n<h3 class=\"editable\">1,4-Addition, also known as conjugate addition, is a nucleophilic addition reaction of \u03b1, \u03b2\u2013unsaturated carbonyl compounds and \u03b1, \u03b2\u2013unsaturated nitriles.<\/h3>\n<p>eg: \u00a0Two nucleophilic addition reaction could occur between methylvinyl ketone (1) and methanethiol in basic medium.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135739\/14addition9.png\" alt=\"14addition9.png\" width=\"600px\" height=\"345px\" \/><\/p>\n<p>mechanism of Reaction 1:<\/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\/3773\/2018\/11\/21135743\/14addition10.png\" alt=\"14addition10.png\" width=\"574\" height=\"460\" \/><\/p>\n<p>The net reaction from <strong>1<\/strong> to <strong>4<\/strong> is the addition of two ligands to atoms <em>1<\/em> and <em>4<\/em> in <strong>1<\/strong>. Hence, the reaction is called 1,4-addition, or conjugate addition, and its product (<strong>2<\/strong>) 1,4-adduct.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135746\/14addition11.png\" alt=\"14addition11.png\" width=\"600px\" height=\"175px\" \/><\/p>\n<p>mechanism of Reaction 2:<\/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\/3773\/2018\/11\/21135750\/14addition12.png\" alt=\"14addition12.png\" width=\"557\" height=\"397\" \/><\/p>\n<p>The net reaction from <strong>1<\/strong> to <strong>3<\/strong> is the addition of two ligands to atoms <em>1<\/em> and <em>2<\/em> in <strong>1<\/strong>. \u00a0Hence, the reaction is called 1,2-addition, or direct addition, and the product (<strong>3<\/strong>) a 1,2-adduct.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/21135754\/14addition13.png\" alt=\"14addition13.png\" width=\"600px\" height=\"162px\" \/><\/p>\n<p>The overall reaction between an \u03b1, \u03b2\u2013unsaturated compound and a nucleophile is regioselective. Whether the dominant process is 1,4-addition or 1,2-addition depends on several factors, such as the alkene-containing reactant (the \u03b1, \u03b2\u2013unsaturated compound), nucleophile, solvent, concentration, temperature, reaction time, and catalyst, if any, making if difficult to make a generalization. Most resonance-stabilized carbon nucleophiles, such as enolate ions and enamines overwhelmingly prefer 1,4-addition to 1,2-addition. (See <a title=\"Michael Addition\" href=\"https:\/\/chem.libretexts.org\/Ancillary_Materials\/Reference\/Organic_Chemistry_Glossary\/Michael_Addition\" rel=\"internal\">Michael addition<\/a>)<\/p>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Introduction to the Molecular Orbitals of Conjugated Alkenes\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/r1LFkcKM6nA?feature=oembed&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-2839 size-thumbnail\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3773\/2018\/11\/07161339\/frame-6-150x150.png\" alt=\"\" width=\"150\" height=\"150\" \/><\/h3>\n<h3 class=\"editable\">Contributors<\/h3>\n<ul>\n<li><a title=\"http:\/\/chemwiki.ucdavis.edu\/Organic_Chemistry\/Organic_Chemistry_With_a_Biological_Emphasis\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\" rel=\"internal\"><strong>Organic Chemistry With a Biological Emphasis\u00a0<\/strong><\/a>by\u00a0<a class=\"external\" title=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" href=\"http:\/\/facultypages.morris.umn.edu\/~soderbt\/\" target=\"_blank\" rel=\"external nofollow noopener\">Tim Soderberg<\/a>\u00a0(University of Minnesota, Morris)<\/li>\n<li><a class=\"external\" title=\"http:\/\/www.uvu.edu\/profpages\/profiles\/show\/user_id\/1776\" href=\"http:\/\/www.uvu.edu\/profpages\/profiles\/show\/user_id\/1776\" target=\"_blank\" rel=\"external nofollow noopener\"><span class=\"gD\">Gamini Gunawardena<\/span><\/a>\u00a0from the\u00a0<a class=\"external\" title=\"http:\/\/science.uvu.edu\/ochem\/\" href=\"http:\/\/science.uvu.edu\/ochem\/\" target=\"_blank\" rel=\"external nofollow noopener\">OChemPal\u00a0<\/a>site (<a class=\"external\" title=\"http:\/\/www.uvu.edu\/chemistry\/\" href=\"http:\/\/www.uvu.edu\/chemistry\/\" target=\"_blank\" rel=\"external nofollow noopener\">Utah Valley University<\/a>)<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n<\/article>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-202\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>14.1: Stability of Conjugated Dienes - Molecular Orbital Theory. <strong>Authored by<\/strong>: Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University)  Prof. Steven Farmer (Sonoma State University)  William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook ofu00a0Organicu00a0Chemistry  u00a0Tim Soderbergu00a0(University of Minnesota, Morris). <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Map%3A_Organic_Chemistry_(McMurry)\/Chapter_14%3A_Conjugated_Compounds_and_Ultraviolet_Spectroscopy\/14.01_Stability_of_Conjugated_Dienes%3A__Molecular_Orbital_Theory\">https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Map%3A_Organic_Chemistry_(McMurry)\/Chapter_14%3A_Conjugated_Compounds_and_Ultraviolet_Spectroscopy\/14.01_Stability_of_Conjugated_Dienes%3A__Molecular_Orbital_Theory<\/a>. <strong>Project<\/strong>: Chemistry LibreTexts. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><li>1,4-Addition. <strong>Authored by<\/strong>: Gamini Gunawardena from the OChemPal site (Utah Valley University). <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/chem.libretexts.org\/Ancillary_Materials\/Reference\/Organic_Chemistry_Glossary\/1%2C4-Addition\">https:\/\/chem.libretexts.org\/Ancillary_Materials\/Reference\/Organic_Chemistry_Glossary\/1%2C4-Addition<\/a>. <strong>Project<\/strong>: Chemistry LibreTexts. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><li>Organic Chemistry With a Biological Emphasis. <strong>Authored by<\/strong>: Tim Soderberg. <strong>Provided by<\/strong>: University of Minnesota, Morris. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\">https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em><\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":311,"menu_order":4,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"14.1: Stability of Conjugated Dienes - Molecular Orbital Theory\",\"author\":\"Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University)  Prof. Steven Farmer (Sonoma State University)  William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook ofu00a0Organicu00a0Chemistry  u00a0Tim Soderbergu00a0(University of Minnesota, Morris)\",\"organization\":\"\",\"url\":\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Map%3A_Organic_Chemistry_(McMurry)\/Chapter_14%3A_Conjugated_Compounds_and_Ultraviolet_Spectroscopy\/14.01_Stability_of_Conjugated_Dienes%3A__Molecular_Orbital_Theory\",\"project\":\"Chemistry LibreTexts\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"},{\"type\":\"cc\",\"description\":\"1,4-Addition\",\"author\":\"Gamini Gunawardena from the OChemPal site (Utah Valley University)\",\"organization\":\"\",\"url\":\"https:\/\/chem.libretexts.org\/Ancillary_Materials\/Reference\/Organic_Chemistry_Glossary\/1%2C4-Addition\",\"project\":\"Chemistry LibreTexts\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"},{\"type\":\"cc\",\"description\":\"Organic Chemistry With a Biological Emphasis\",\"author\":\"Tim Soderberg\",\"organization\":\"University of Minnesota, Morris\",\"url\":\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry\/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-202","chapter","type-chapter","status-publish","hentry"],"part":313,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/chapters\/202","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":20,"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/chapters\/202\/revisions"}],"predecessor-version":[{"id":2980,"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/chapters\/202\/revisions\/2980"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/parts\/313"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/chapters\/202\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/wp\/v2\/media?parent=202"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/pressbooks\/v2\/chapter-type?post=202"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/wp\/v2\/contributor?post=202"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/wp-json\/wp\/v2\/license?post=202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}