{"id":811,"date":"2017-10-19T15:38:58","date_gmt":"2017-10-19T15:38:58","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/?post_type=chapter&#038;p=811"},"modified":"2017-10-19T15:38:58","modified_gmt":"2017-10-19T15:38:58","slug":"meso-compounds","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/chapter\/meso-compounds\/","title":{"raw":"Meso Compounds","rendered":"Meso Compounds"},"content":{"raw":"<div class=\"elm-header\"><\/div>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div id=\"skills\">\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Objectives<\/h3>\r\nAfter completing this section, you should be able to\r\n<ol>\r\n \t<li>determine whether or not a compound containing two chiral carbon atoms will have a meso form, given its Kekul\u00e9, condensed or shorthand structure, or its IUPAC name.<\/li>\r\n \t<li>draw wedge-and-broken-line structures for the enantiomers and meso form of a compound such as tartaric acid, given its IUPAC name, or its Kekul\u00e9, condensed or shorthand structure.<\/li>\r\n \t<li>make a general comparison of the physical properties of the enantiomers, meso form and racemic mixture of a compound such as tartaric acid.<\/li>\r\n<\/ol>\r\n<\/div>\r\n\r\n\r\n<\/div>\r\n<div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Term<\/h3>\r\nMake certain that you can define, and use in context, the key term below.\r\n<ul>\r\n \t<li>meso compound<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox\">\r\n<div id=\"note\">\r\n<h3 class=\"boxtitle\">Study Notes<\/h3>\r\nYou may be confused by the two sets of structures showing \u201crotations.\u201d Of course in each case the two structures shown are identical, they represent the same molecule looked at from two different perspectives. In the first case, there is a 120\u00b0 rotation around the single carbon-carbon bond. In the second, the whole molecule is rotated 180\u00b0 top to bottom.\r\n\r\n<\/div>\r\n<\/div>\r\n\r\n\r\n<\/div>\r\n<a href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Stereoisomers\/Chirality_and_Symmetry\/Meso_Compounds\" target=\"_blank\" rel=\"internal noopener\">Meso Compounds<\/a>\r\n\r\nA meso compound is an achiral compound that has chiral centers. It is superimposed on its mirror image and is optically <strong>inactive <\/strong>although it contains two or more stereocenters.\r\n<div id=\"section_1\">\r\n\r\n\r\n<h3 class=\"editable\">Introduction<\/h3>\r\nIn general, a meso compound should contain two or more identical substituted stereocenters. Also, it has an internal symmetry plane that divides the compound in half. These two halves reflect each other by the internal mirror. The stereochemistry of stereocenters should \"cancel out\". What it means here is that when we have an internal plane that splits the compound into two symmetrical sides, the stereochemistry of both left and right side should be opposite to each other, and therefore, result in <strong>optically inactive<\/strong>. Cyclic compounds may also be meso.\r\n\r\n<\/div>\r\n<div id=\"section_2\">\r\n\r\n\r\n<h3 class=\"editable\">Identification<\/h3>\r\nIf A is a meso compound, it should have two or more stereocenters, an internal plane, and the stereochemistry should be <a title=\"Absolute Configuration: R-S Sequence Rules\" href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Absolute_Configuration%2C_R-S_Sequence_Rules\" rel=\"internal\">R and S<\/a>.\r\n<ol>\r\n \t<li>Look for an internal plane, or internal mirror, that lies in between the compound.<\/li>\r\n \t<li>The stereochemistry (e.g. R\u00a0or S) is very crucial in determining whether it is a meso compound or not. As mentioned above, a meso compound is optically inactive, so their stereochemistry should cancel out. For instance, R cancels S\u00a0out in a meso compound with two stereocenters.<\/li>\r\n<\/ol>\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1573\/Meso1_(1).bmp?revision=1&amp;size=bestfit&amp;width=375&amp;height=171#fixme\" alt=\"Meso1 (1).bmp\" width=\"375px\" height=\"171px\" \/>\r\n\r\n<strong><em>trans<\/em>-1,2-dichloro-1,2-ethanediol<\/strong>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1574\/Meso2_(5).bmp?revision=1&amp;size=bestfit&amp;width=433&amp;height=183#fixme\" alt=\"Meso2 (5).bmp\" width=\"433px\" height=\"183px\" \/>\r\n\r\n<em><strong>(meso)<\/strong><\/em><strong>-2,3-dibromobutane<\/strong>\r\n\r\n<u>Tips:<\/u> An interesting thing about single bonds or sp<sup>3<\/sup>-orbitals is that we can rotate the substituted groups that attached to a stereocenter around to recognize the internal plane. As the molecule is rotated, its stereochemistry does not change. For example:\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1577\/rotated_(1).bmp?revision=1&amp;size=bestfit&amp;width=412&amp;height=258#fixme\" alt=\"rotated (1).bmp\" width=\"412px\" height=\"258px\" \/>\r\n\r\nAnother case is when we rotate the whole molecule by 180 degree. Both molecules below are still meso.\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1578\/rotated180.bmp?revision=1&amp;size=bestfit&amp;width=481&amp;height=245#fixme\" alt=\"rotated180.bmp\" width=\"481px\" height=\"245px\" \/>\r\n\r\nRemember the internal plane here is depicted on two dimensions. However, in reality, it is three dimensions, so be aware of it when we identify the internal mirror.\r\n<div>\r\n<div id=\"example\">\r\n<div class=\"textbox examples\">\r\n<h3>Example<\/h3>\r\n<p class=\"boxtitle\"><\/p>\r\n<img class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132559\/mesocompound1.png\" alt=\"\" width=\"237\" height=\"207\" \/>\r\n\r\n[reveal-answer q=\"806393\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"806393\"]1 has a plane of symmetry (the horizonatal plane going through the red broken line) and, therefore, is achiral;\u00a01 has chiral centers. \u00a0Thus,\u00a01 is a meso compound.[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div class=\"textbox examples\">\r\n<h3>Example<\/h3>\r\n<div id=\"section_2\">\r\n\r\n<img class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132602\/mesocompound2.png\" alt=\"\" width=\"322\" height=\"118\" \/>\r\n\r\n[reveal-answer q=\"403693\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"403693\"]This molecules has a plane of symmetry (the vertical plane going through the red broken line perpendicular to the plane of the ring) and, therefore, is achiral, but has has two chiral centers. Thus, its is a meso compound.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"section_3\"><\/div>\r\n<\/div>\r\n\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_3\">\r\n<h3 class=\"editable\">Other Examples of meso compounds<\/h3>\r\nMeso compounds can exist in many different forms such as pentane, butane, heptane, and even cyclobutane. They do not necessarily have to be two stereocenters, but can have more.\r\n\r\n<u><strong><img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1575\/Meso3_(1).bmp?revision=1&amp;size=bestfit&amp;width=695&amp;height=176#fixme\" alt=\"Meso3 (1).bmp\" width=\"695px\" height=\"176px\" \/><\/strong><\/u>\r\n\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1572\/Cyclic.bmp?revision=1&amp;size=bestfit&amp;width=621&amp;height=231#fixme\" alt=\"Cyclic.bmp\" width=\"621px\" height=\"231px\" \/>\r\n\r\n<\/div>\r\n<div id=\"section_4\">\r\n\r\n\r\n<h3 class=\"editable\">Optical Activity Analysis<\/h3>\r\nWhen the <a title=\"Organic Chemistry\/Chirality\/Optical Activity\" href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Optical_Activity\" rel=\"internal\">optical activity<\/a> of a meso compound is attempted to be determined with a polarimeter, the indicator will not show (+) or (-). It simply means there is no certain direction of rotation of the polarized light, neither levorotatory (-) and dexorotatory (+).\r\n\r\n<\/div>\r\n<div id=\"section_5\">\r\n\r\n\r\n<h3 class=\"editable\">Achiral Diastereomers (meso-Compounds)<\/h3>\r\nThe chiral centers in the preceding examples have all been different. In the case of 2,3-dihydroxybutanedioic acid, known as tartaric acid, the two chiral centers have the same four substituents and are equivalent. As a result, two of the four possible stereoisomers of this compound are identical due to a plane of symmetry, so there are only three stereoisomeric tartaric acids. Two of these stereoisomers are enantiomers and the third is an achiral diastereomer, called a <strong>meso<\/strong> compound. Meso compounds are achiral (optically inactive) diastereomers of chiral stereoisomers. Investigations of isomeric tartaric acid salts, carried out by <a class=\"external\" href=\"http:\/\/www.chemistry.msu.edu\/Portraits\/PortraitsHH_Detail.asp?HH_LName=Pasteur\" target=\"_blank\" rel=\"external nofollow noopener\">Louis Pasteur<\/a> in the mid 19th century, were instrumental in elucidating some of the subtleties of stereochemistry. Some physical properties of the isomers of tartaric acid are given in the following table.\r\n<table style=\"border-spacing: 4px;width: 320px\">\r\n<tbody>\r\n<tr>\r\n<td>(+)-tartaric acid:<\/td>\r\n<td>[\u03b1]<sub>D<\/sub> = +13\u00ba<\/td>\r\n<td>m.p. 172 \u00baC<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>(\u2013)-tartaric acid:<\/td>\r\n<td>[\u03b1]<sub>D<\/sub> = \u201313\u00ba<\/td>\r\n<td>m.p. 172 \u00baC<\/td>\r\n<\/tr>\r\n<tr>\r\n<td><em>meso<\/em>-tartaric acid:<\/td>\r\n<td>[\u03b1]<sub>D<\/sub> = 0\u00ba<\/td>\r\n<td>m.p. 140 \u00baC<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nFischer projection formulas provide a helpful view of the configurational relationships within the structures of these isomers. In the following illustration a mirror line is drawn between formulas that have a mirror-image relationship. In demonstrating the identity of the two meso-compound formulas, remember that a Fischer projection formula may be rotated 180\u00ba in the plane.\r\n<p style=\"text-align: center\"><img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132604\/tartaric.gif\" alt=\"tartaric.gif\" \/><\/p>\r\n\r\n<\/div>\r\n<div id=\"section_6\">\r\n\r\n\r\n<div class=\"textbox examples\">\r\n<h3>Examples<\/h3>\r\n<div id=\"section_6\">\r\n<h3 class=\"editable\">Problems<\/h3>\r\nBeside meso, there are also other types of molecules: <a title=\"Enantiomers\" rel=\"broken\">enantiomer<\/a>, <a title=\"Diastereomers\" href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Diastereomers\" rel=\"internal\">diastereomer<\/a>, and identical. Determine if the following molecules are meso.\r\n\r\n<img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1576\/Mesopracticeprob.bmp?revision=1&amp;size=bestfit&amp;width=657&amp;height=377#fixme\" alt=\"Mesopracticeprob.bmp\" width=\"657px\" height=\"377px\" \/>\r\n\r\n[reveal-answer q=\"324740\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"324740\"]Answer key: A\u00a0C, D, E are meso compounds.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"section_7\"><\/div>\r\n<\/div>\r\n\r\n\r\n<\/div>\r\n<div id=\"section_7\">\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<div id=\"s61692\">\r\n<div id=\"section_22\">\r\n\r\n\r\n<h3 id=\"Questions-61692\">Question<\/h3>\r\n<span>Which of the following are meso-compounds:<\/span>\r\n\r\n<span><img class=\"internal default\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132606\/5.7.png\" alt=\"\" width=\"372\" height=\"188\" \/><\/span>\r\n\r\n<span><span>C \u2013 2,3-dibromobutane<\/span><\/span>\r\n\r\n<span><span>D \u2013 2,3-dibromopentane<\/span><\/span>\r\n\r\n<\/div>\r\n<div id=\"section_23\">\r\n\r\n\r\n<h3 id=\"Solutions-61692\">Solutions<\/h3>\r\n<span><span>Compounds A and D are meso.<\/span><\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n\r\n\r\n<\/div>\r\n<div id=\"section_8\">\r\n\r\n\r\n<h3 class=\"editable\">Contributors<\/h3>\r\n<ul>\r\n \t<li>Duy Dang<\/li>\r\n \t<li>\r\n<ul>\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> from the <a class=\"external\" title=\"http:\/\/science.uvu.edu\/ochem\/\" href=\"http:\/\/science.uvu.edu\/ochem\/\" target=\"_blank\" rel=\"external nofollow noopener\">OChemPal <\/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<\/li>\r\n \t<li>William Reusch, Professor Emeritus (<a class=\"external\" title=\"http:\/\/www.msu.edu\/\" href=\"http:\/\/www.msu.edu\/\" target=\"_blank\" rel=\"external nofollow noopener\">Michigan State U.<\/a>), <a class=\"external\" title=\"http:\/\/www.cem.msu.edu\/~reusch\/VirtualText\/intro1.htm\" href=\"http:\/\/www.cem.msu.edu\/%7Ereusch\/VirtualText\/intro1.htm\" target=\"_blank\" rel=\"external nofollow noopener\">Virtual Textbook of\u00a0Organic\u00a0Chemistry<\/a><\/li>\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<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"elm-header\"><\/div>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div id=\"skills\">\n<div class=\"textbox learning-objectives\">\n<h3>Objectives<\/h3>\n<p>After completing this section, you should be able to<\/p>\n<ol>\n<li>determine whether or not a compound containing two chiral carbon atoms will have a meso form, given its Kekul\u00e9, condensed or shorthand structure, or its IUPAC name.<\/li>\n<li>draw wedge-and-broken-line structures for the enantiomers and meso form of a compound such as tartaric acid, given its IUPAC name, or its Kekul\u00e9, condensed or shorthand structure.<\/li>\n<li>make a general comparison of the physical properties of the enantiomers, meso form and racemic mixture of a compound such as tartaric acid.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Term<\/h3>\n<p>Make certain that you can define, and use in context, the key term below.<\/p>\n<ul>\n<li>meso compound<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox\">\n<div id=\"note\">\n<h3 class=\"boxtitle\">Study Notes<\/h3>\n<p>You may be confused by the two sets of structures showing \u201crotations.\u201d Of course in each case the two structures shown are identical, they represent the same molecule looked at from two different perspectives. In the first case, there is a 120\u00b0 rotation around the single carbon-carbon bond. In the second, the whole molecule is rotated 180\u00b0 top to bottom.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<p><a href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Stereoisomers\/Chirality_and_Symmetry\/Meso_Compounds\" target=\"_blank\" rel=\"internal noopener\">Meso Compounds<\/a><\/p>\n<p>A meso compound is an achiral compound that has chiral centers. It is superimposed on its mirror image and is optically <strong>inactive <\/strong>although it contains two or more stereocenters.<\/p>\n<div id=\"section_1\">\n<h3 class=\"editable\">Introduction<\/h3>\n<p>In general, a meso compound should contain two or more identical substituted stereocenters. Also, it has an internal symmetry plane that divides the compound in half. These two halves reflect each other by the internal mirror. The stereochemistry of stereocenters should &#8220;cancel out&#8221;. What it means here is that when we have an internal plane that splits the compound into two symmetrical sides, the stereochemistry of both left and right side should be opposite to each other, and therefore, result in <strong>optically inactive<\/strong>. Cyclic compounds may also be meso.<\/p>\n<\/div>\n<div id=\"section_2\">\n<h3 class=\"editable\">Identification<\/h3>\n<p>If A is a meso compound, it should have two or more stereocenters, an internal plane, and the stereochemistry should be <a title=\"Absolute Configuration: R-S Sequence Rules\" href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Absolute_Configuration%2C_R-S_Sequence_Rules\" rel=\"internal\">R and S<\/a>.<\/p>\n<ol>\n<li>Look for an internal plane, or internal mirror, that lies in between the compound.<\/li>\n<li>The stereochemistry (e.g. R\u00a0or S) is very crucial in determining whether it is a meso compound or not. As mentioned above, a meso compound is optically inactive, so their stereochemistry should cancel out. For instance, R cancels S\u00a0out in a meso compound with two stereocenters.<\/li>\n<\/ol>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1573\/Meso1_(1).bmp?revision=1&amp;size=bestfit&amp;width=375&amp;height=171#fixme\" alt=\"Meso1 (1).bmp\" width=\"375px\" height=\"171px\" \/><\/p>\n<p><strong><em>trans<\/em>-1,2-dichloro-1,2-ethanediol<\/strong><\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1574\/Meso2_(5).bmp?revision=1&amp;size=bestfit&amp;width=433&amp;height=183#fixme\" alt=\"Meso2 (5).bmp\" width=\"433px\" height=\"183px\" \/><\/p>\n<p><em><strong>(meso)<\/strong><\/em><strong>-2,3-dibromobutane<\/strong><\/p>\n<p><u>Tips:<\/u> An interesting thing about single bonds or sp<sup>3<\/sup>-orbitals is that we can rotate the substituted groups that attached to a stereocenter around to recognize the internal plane. As the molecule is rotated, its stereochemistry does not change. For example:<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1577\/rotated_(1).bmp?revision=1&amp;size=bestfit&amp;width=412&amp;height=258#fixme\" alt=\"rotated (1).bmp\" width=\"412px\" height=\"258px\" \/><\/p>\n<p>Another case is when we rotate the whole molecule by 180 degree. Both molecules below are still meso.<\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1578\/rotated180.bmp?revision=1&amp;size=bestfit&amp;width=481&amp;height=245#fixme\" alt=\"rotated180.bmp\" width=\"481px\" height=\"245px\" \/><\/p>\n<p>Remember the internal plane here is depicted on two dimensions. However, in reality, it is three dimensions, so be aware of it when we identify the internal mirror.<\/p>\n<div>\n<div id=\"example\">\n<div class=\"textbox examples\">\n<h3>Example<\/h3>\n<p class=\"boxtitle\">\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132559\/mesocompound1.png\" alt=\"\" width=\"237\" height=\"207\" \/><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q806393\">Show Answer<\/span><\/p>\n<div id=\"q806393\" class=\"hidden-answer\" style=\"display: none\">1 has a plane of symmetry (the horizonatal plane going through the red broken line) and, therefore, is achiral;\u00a01 has chiral centers. \u00a0Thus,\u00a01 is a meso compound.<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div class=\"textbox examples\">\n<h3>Example<\/h3>\n<div id=\"section_2\">\n<p><img loading=\"lazy\" decoding=\"async\" class=\"internal aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132602\/mesocompound2.png\" alt=\"\" width=\"322\" height=\"118\" \/><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q403693\">Show Answer<\/span><\/p>\n<div id=\"q403693\" class=\"hidden-answer\" style=\"display: none\">This molecules has a plane of symmetry (the vertical plane going through the red broken line perpendicular to the plane of the ring) and, therefore, is achiral, but has has two chiral centers. Thus, its is a meso compound.<\/div>\n<\/div>\n<\/div>\n<div id=\"section_3\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_3\">\n<h3 class=\"editable\">Other Examples of meso compounds<\/h3>\n<p>Meso compounds can exist in many different forms such as pentane, butane, heptane, and even cyclobutane. They do not necessarily have to be two stereocenters, but can have more.<\/p>\n<p><u><strong><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1575\/Meso3_(1).bmp?revision=1&amp;size=bestfit&amp;width=695&amp;height=176#fixme\" alt=\"Meso3 (1).bmp\" width=\"695px\" height=\"176px\" \/><\/strong><\/u><\/p>\n<p><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1572\/Cyclic.bmp?revision=1&amp;size=bestfit&amp;width=621&amp;height=231#fixme\" alt=\"Cyclic.bmp\" width=\"621px\" height=\"231px\" \/><\/p>\n<\/div>\n<div id=\"section_4\">\n<h3 class=\"editable\">Optical Activity Analysis<\/h3>\n<p>When the <a title=\"Organic Chemistry\/Chirality\/Optical Activity\" href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Optical_Activity\" rel=\"internal\">optical activity<\/a> of a meso compound is attempted to be determined with a polarimeter, the indicator will not show (+) or (-). It simply means there is no certain direction of rotation of the polarized light, neither levorotatory (-) and dexorotatory (+).<\/p>\n<\/div>\n<div id=\"section_5\">\n<h3 class=\"editable\">Achiral Diastereomers (meso-Compounds)<\/h3>\n<p>The chiral centers in the preceding examples have all been different. In the case of 2,3-dihydroxybutanedioic acid, known as tartaric acid, the two chiral centers have the same four substituents and are equivalent. As a result, two of the four possible stereoisomers of this compound are identical due to a plane of symmetry, so there are only three stereoisomeric tartaric acids. Two of these stereoisomers are enantiomers and the third is an achiral diastereomer, called a <strong>meso<\/strong> compound. Meso compounds are achiral (optically inactive) diastereomers of chiral stereoisomers. Investigations of isomeric tartaric acid salts, carried out by <a class=\"external\" href=\"http:\/\/www.chemistry.msu.edu\/Portraits\/PortraitsHH_Detail.asp?HH_LName=Pasteur\" target=\"_blank\" rel=\"external nofollow noopener\">Louis Pasteur<\/a> in the mid 19th century, were instrumental in elucidating some of the subtleties of stereochemistry. Some physical properties of the isomers of tartaric acid are given in the following table.<\/p>\n<table style=\"border-spacing: 4px;width: 320px\">\n<tbody>\n<tr>\n<td>(+)-tartaric acid:<\/td>\n<td>[\u03b1]<sub>D<\/sub> = +13\u00ba<\/td>\n<td>m.p. 172 \u00baC<\/td>\n<\/tr>\n<tr>\n<td>(\u2013)-tartaric acid:<\/td>\n<td>[\u03b1]<sub>D<\/sub> = \u201313\u00ba<\/td>\n<td>m.p. 172 \u00baC<\/td>\n<\/tr>\n<tr>\n<td><em>meso<\/em>-tartaric acid:<\/td>\n<td>[\u03b1]<sub>D<\/sub> = 0\u00ba<\/td>\n<td>m.p. 140 \u00baC<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Fischer projection formulas provide a helpful view of the configurational relationships within the structures of these isomers. In the following illustration a mirror line is drawn between formulas that have a mirror-image relationship. In demonstrating the identity of the two meso-compound formulas, remember that a Fischer projection formula may be rotated 180\u00ba in the plane.<\/p>\n<p style=\"text-align: center\"><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132604\/tartaric.gif\" alt=\"tartaric.gif\" \/><\/p>\n<\/div>\n<div id=\"section_6\">\n<div class=\"textbox examples\">\n<h3>Examples<\/h3>\n<div id=\"section_6\">\n<h3 class=\"editable\">Problems<\/h3>\n<p>Beside meso, there are also other types of molecules: <a title=\"Enantiomers\" rel=\"broken\">enantiomer<\/a>, <a title=\"Diastereomers\" href=\"https:\/\/chem.libretexts.org\/Core\/Organic_Chemistry\/Chirality\/Diastereomers\" rel=\"internal\">diastereomer<\/a>, and identical. Determine if the following molecules are meso.<\/p>\n<p><img decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1576\/Mesopracticeprob.bmp?revision=1&amp;size=bestfit&amp;width=657&amp;height=377#fixme\" alt=\"Mesopracticeprob.bmp\" width=\"657px\" height=\"377px\" \/><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q324740\">Show Answer<\/span><\/p>\n<div id=\"q324740\" class=\"hidden-answer\" style=\"display: none\">Answer key: A\u00a0C, D, E are meso compounds.<\/div>\n<\/div>\n<\/div>\n<div id=\"section_7\"><\/div>\n<\/div>\n<\/div>\n<div id=\"section_7\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<div id=\"s61692\">\n<div id=\"section_22\">\n<h3 id=\"Questions-61692\">Question<\/h3>\n<p><span>Which of the following are meso-compounds:<\/span><\/p>\n<p><span><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\/05132606\/5.7.png\" alt=\"\" width=\"372\" height=\"188\" \/><\/span><\/p>\n<p><span><span>C \u2013 2,3-dibromobutane<\/span><\/span><\/p>\n<p><span><span>D \u2013 2,3-dibromopentane<\/span><\/span><\/p>\n<\/div>\n<div id=\"section_23\">\n<h3 id=\"Solutions-61692\">Solutions<\/h3>\n<p><span><span>Compounds A and D are meso.<\/span><\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_8\">\n<h3 class=\"editable\">Contributors<\/h3>\n<ul>\n<li>Duy Dang<\/li>\n<li>\n<ul>\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> from the <a class=\"external\" title=\"http:\/\/science.uvu.edu\/ochem\/\" href=\"http:\/\/science.uvu.edu\/ochem\/\" target=\"_blank\" rel=\"external nofollow noopener\">OChemPal <\/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<\/li>\n<li>William Reusch, Professor Emeritus (<a class=\"external\" title=\"http:\/\/www.msu.edu\/\" href=\"http:\/\/www.msu.edu\/\" target=\"_blank\" rel=\"external nofollow noopener\">Michigan State U.<\/a>), <a class=\"external\" title=\"http:\/\/www.cem.msu.edu\/~reusch\/VirtualText\/intro1.htm\" href=\"http:\/\/www.cem.msu.edu\/%7Ereusch\/VirtualText\/intro1.htm\" target=\"_blank\" rel=\"external nofollow noopener\">Virtual Textbook of\u00a0Organic\u00a0Chemistry<\/a><\/li>\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<\/ul>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":44985,"menu_order":7,"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-811","chapter","type-chapter","status-publish","hentry"],"part":22,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/811","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":4,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/811\/revisions"}],"predecessor-version":[{"id":2061,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/811\/revisions\/2061"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/parts\/22"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/811\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/media?parent=811"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=811"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/contributor?post=811"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/license?post=811"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}