{"id":803,"date":"2017-10-19T15:42:53","date_gmt":"2017-10-19T15:42:53","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/?post_type=chapter&#038;p=803"},"modified":"2018-10-03T18:07:48","modified_gmt":"2018-10-03T18:07:48","slug":"diastereomers","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/chapter\/diastereomers\/","title":{"raw":"Diastereomers","rendered":"Diastereomers"},"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>calculate the maximum number of stereoisomers possible for a compound containing a specified number of chiral carbon atoms.<\/li>\r\n \t<li>draw wedge-and-broken-line structures for all possible stereoisomers of a compound containing two chiral carbon atoms, with or without the aid of molecular models.<\/li>\r\n \t<li>assign <em>R<\/em>,<em>S<\/em> configurations to wedge-and-broken-line structures containing two chiral carbon atoms, with or without the aid of molecular models.<\/li>\r\n \t<li>determine, with or without the aid of molecular models, whether two wedge-and-broken-line structures containing two chiral carbon atoms are identical, represent a pair of enantiomers, or represent a pair of diastereomers.<\/li>\r\n \t<li>draw the wedge-and-broken-line structure of a specific stereoisomer of a compound containing two chiral carbon atoms, given its IUPAC name and <em>R<\/em>,<em>S<\/em> configuration.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>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 term below.\r\n<ul>\r\n \t<li>diastereomer<\/li>\r\n<\/ul>\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\r\nDiastereomers are stereoisomers that are not related as object and mirror image and are not <a title=\"Organic Chemistry\/Organic Chemistry With a Biological Emphasis\/Chapter 3: Conformations and Stereochemistry\/Section 3.3: Stereoisomerism \u2013 chirality, stereocenters, enantiomers\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\/Chapter_03%3A_Conformations_and_Stereochemistry\/03.3%3A_Stereoisomerism_%E2%80%93_chirality%2C_stereocenters%2C_enantiomers\" rel=\"internal\"><span class=\"internal\">enantiomers<\/span><\/a>. Unlike enatiomers which <strong>are mirror images<\/strong> of each other and <strong>non-sumperimposable<\/strong>, diastereomers are <strong>not mirror images<\/strong> of each other and <strong>non-superimposable<\/strong>. Diastereomers can have different physical properties and reactivity. They have different melting points and boiling points and different densities. They have <strong>two or more<\/strong> stereocenters.\r\n<div id=\"section_1\">\r\n<h3 class=\"editable\">Introduction<\/h3>\r\nIt is easy to mistake between diasteromers and enantiomers. For example, we have four steroisomers of 3-bromo-2-butanol. The four possible combination are SS, RR, SR and RS (Figure 5.6.1). One of the molecule is the enantiomer of its mirror image molecule and diasteromer of each of the other two molecule (SS is enantiomer of RR and diasteromer of RS and SR). SS's mirror image is RR and they are not superimposable, so they are enantiomers. RS and SR are not mirror image of SS and are not superimposable to each other, so they are diasteromers.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"850\"]<a title=\"chem (1).png\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1550\/chem_(1).png?revision=1\" rel=\"internal\"><img class=\"internal default\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132415\/chem_1.png\" alt=\"chem (1).png\" width=\"850\" height=\"613\" \/><\/a> Figure 1[\/caption]\r\n\r\n<\/div>\r\n<div id=\"section_2\">\r\n<h3 class=\"editable\">Diastereomers vs. Enantiomers<\/h3>\r\nTartaric acid, C<sub>4<\/sub>H<sub>6<\/sub>O<sub>6<\/sub><sub>,<\/sub> is an organic compound that can be found in grape, bananas, and in wine. The structures of tartaric acid itself is really interesting. Naturally, it is in the form of (R,R) stereocenters. Artificially, it can be in the meso form (R,S), which is achiral. R,R tartaric acid is enantiomer to is mirror image which is S,S tartaric acid and diasteromers to meso-tartaric acid (Figure 5.6.2).\r\n\r\n(R,R) and (S,S) tartaric acid have similar physical properties and reactivity. However, meso-tartaric acid have different physical properties and reactivity. For example, melting point of (R,R) &amp; (S,S) tartaric is about 170 degree Celsius, and melting point of meso-tartaric acid is about 145 degree Celsius.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"770\"]<a title=\"chem1 (1).bmp\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1551\/chem1_(1).bmp?revision=1\" rel=\"internal\"><img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1551\/chem1_(1).bmp?revision=1&amp;size=bestfit&amp;width=720&amp;height=567#fixme\" alt=\"chem1 (1).bmp\" width=\"770\" height=\"607\" \/><\/a> Figure 2[\/caption]\r\n\r\nWe turn our attention next to molecules which have more than one stereocenter. We will start with a common four-carbon sugar called D-erythrose.\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\/05132418\/image126.png\" alt=\"image126.png\" width=\"211px\" height=\"123px\" \/>\r\n<div>\r\n\r\nA note on sugar nomenclature: biochemists use a special system to refer to the stereochemistry of sugar molecules, employing names of historical origin in addition to the designators '<em>D<\/em>' and '<em>L<\/em>'.\u00a0 You will learn about this system if you take a biochemistry class.\u00a0 We will use the <em>D\/L<\/em> designations here to refer to different sugars, but we won't worry about learning the system.\r\n\r\n<\/div>\r\nAs you can see, <em>D<\/em>-erythrose is a chiral molecule: C<sub>2<\/sub> and C<sub>3<\/sub> are stereocenters, both of which have the <em>R<\/em> configuration. In addition, you should make a model to convince yourself that it is impossible to find a plane of symmetry through the molecule, regardless of the conformation.\u00a0 Does D-erythrose have an enantiomer?\u00a0 Of course it does \u2013 if it is a chiral molecule, it must.\u00a0 The enantiomer of erythrose is its mirror image, and is named L-erythrose (once again, you should use models to convince yourself that these mirror images of erythrose are not superimposable).\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\/05132420\/image128.png\" alt=\"image128.png\" width=\"442px\" height=\"185px\" \/>\r\n\r\nNotice that both chiral centers in L-erythrose both have the <em>S<\/em> configuration.\r\n<div id=\"note\">\r\n<p class=\"boxtitle\">Note: In a pair of enantiomers, <strong>all <\/strong>of the chiral centers are of the opposite configuration.<\/p>\r\n\r\n<\/div>\r\nWhat happens if we draw a stereoisomer of erythrose in which the configuration is <em>S<\/em> at C<sub>2<\/sub> and <em>R<\/em> at C<sub>3<\/sub>?\u00a0 This stereoisomer, which is a sugar called D-threose, is <em>not<\/em> a mirror image of erythrose. D-threose is a <strong>diastereomer<\/strong> of both D-erythrose and L-erythrose.\r\n\r\n<a title=\"image129.png\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/31721\/image129.png?revision=1\" rel=\"internal\"><img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132422\/image129.png\" alt=\"image129.png\" width=\"550px\" height=\"341px\" \/><\/a>\r\n\r\nThe definition of diastereomers is simple: if two molecules are stereoisomers (same molecular formula, same connectivity, different arrangement of atoms in space) but are <em>not<\/em> enantiomers, then they are diastereomers by default. <em>In practical terms, this means that at least one - but not all - of the chiral centers are opposite in a pair of diastereomers.\u00a0<\/em> By definition, two molecules that are diastereomers are <em>not<\/em> mirror images of each other.\r\n\r\nL-threose, the enantiomer of D-threose, has the <em>R<\/em> configuration at C<sub>2<\/sub> and the <em>S<\/em> configuration at C<sub>3<\/sub>.\u00a0 L-threose is a diastereomer of both erythrose enantiomers.\r\n\r\nIn general, a structure with <em>n<\/em> stereocenters will have 2<sup>n<\/sup> different stereoisomers. (We are not considering, for the time being, the stereochemistry of double bonds \u2013 that will come later).\u00a0\u00a0 For example, let's consider the glucose molecule in its open-chain form (recall that many sugar molecules can exist in either an open-chain or a cyclic form). There are two enantiomers of glucose, called D-glucose and L-glucose.\u00a0 The D-enantiomer is the common sugar that our bodies use for energy. It has <em>n<\/em> = 4 stereocenters, so therefore there are 2<sup>n<\/sup> = 2<sup>4<\/sup> = 16 possible stereoisomers (including D-glucose itself).\r\n\r\n<a title=\"image130.png\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/31720\/image130.png?revision=1\" rel=\"internal\"><img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132424\/image130.png\" alt=\"image130.png\" width=\"550px\" height=\"353px\" \/><\/a>\r\n\r\nIn L-glucose, all of the stereocenters are inverted relative to <em>D<\/em>-glucose.\u00a0 That\u00a0 leaves 14 diastereomers of D-glucose: these are molecules in which at least one, but not all, of the stereocenters are inverted relative to D-glucose.\u00a0 One of these 14 diastereomers, a sugar called <em>D<\/em>-galactose, is shown above:\u00a0 in D-galactose, one of four stereocenters is inverted relative to D-glucose. Diastereomers which differ in only one stereocenter (out of two or more)\u00a0 are called <strong>epimers<\/strong>. D-glucose and D-galactose can therefore be refered to as epimers as well as diastereomers.\r\n<div style=\"margin: auto\">\r\n<div id=\"example\">\r\n<div class=\"textbox examples\">\r\n<h3>Example<\/h3>\r\nDraw the structure of\u00a0L-galactose, the\u00a0enantiomer\u00a0of\u00a0D-galactose.\r\n\r\nDraw the structure of two more\u00a0diastereomers\u00a0of D-glucose. One should be an\u00a0epimer.\r\n<dl>\r\n \t<dt><strong>Solution:<\/strong><\/dt>\r\n<\/dl>\r\n<img class=\"internal default alignnone\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132427\/5-6-1.png\" alt=\"\" width=\"451px\" height=\"425px\" \/><\/div>\r\n<div><\/div>\r\n<\/div>\r\n<\/div>\r\n<div>Erythronolide B, a precursor to the 'macrocyclic' antibiotic erythromycin, has 10 stereocenters.\u00a0 It\u2019s enantiomer is that molecule in which all 10 stereocenters are inverted.<\/div>\r\n<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132429\/image136.png\" alt=\"image136.png\" width=\"262px\" height=\"307px\" \/>\r\n\r\nIn total, there are 2<sup>10 <\/sup>= 1024 stereoisomers in the erythronolide B family: 1022 of these are diastereomers of the structure above, one is the enantiomer of the structure above, and the last\u00a0 <strong><em>is <\/em><\/strong>the structure above.\r\n\r\nWe know that enantiomers have identical physical properties and equal but opposite degrees of specific rotation.\u00a0 Diastereomers, in theory at least, have different physical properties \u2013 we stipulate \u2018in theory\u2019 because sometimes the physical properties of two or more diastereomers are so similar that it is very difficult to separate them.\u00a0 In addition, the specific rotations of diastereomers are unrelated \u2013 they could be the same sign or opposite signs, and similar in magnitude or very dissimilar.\r\n\r\n<\/div>\r\n<div id=\"section_3\">\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<div id=\"section_3\">\r\n<div id=\"s61692\">\r\n<div id=\"section_18\">\r\n\r\nDetermine the stereochemistry of the following molecule:\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\/05132431\/5.6qu.png\" alt=\"\" width=\"349\" height=\"156\" \/>\r\n\r\n<\/div>\r\n<div id=\"section_19\">\r\n<h3 id=\"Solutions-61692\">Solutions<\/h3>\r\n[reveal-answer q=\"622472\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"622472\"]<img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132433\/5.6sol.png\" alt=\"\" width=\"331\" height=\"148\" \/>[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_4\"><\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"section_4\">\r\n<h3 class=\"editable\">Contributors<\/h3>\r\n<ul>\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 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&nbsp;","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>calculate the maximum number of stereoisomers possible for a compound containing a specified number of chiral carbon atoms.<\/li>\n<li>draw wedge-and-broken-line structures for all possible stereoisomers of a compound containing two chiral carbon atoms, with or without the aid of molecular models.<\/li>\n<li>assign <em>R<\/em>,<em>S<\/em> configurations to wedge-and-broken-line structures containing two chiral carbon atoms, with or without the aid of molecular models.<\/li>\n<li>determine, with or without the aid of molecular models, whether two wedge-and-broken-line structures containing two chiral carbon atoms are identical, represent a pair of enantiomers, or represent a pair of diastereomers.<\/li>\n<li>draw the wedge-and-broken-line structure of a specific stereoisomer of a compound containing two chiral carbon atoms, given its IUPAC name and <em>R<\/em>,<em>S<\/em> configuration.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>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 term below.<\/p>\n<ul>\n<li>diastereomer<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<p>Diastereomers are stereoisomers that are not related as object and mirror image and are not <a title=\"Organic Chemistry\/Organic Chemistry With a Biological Emphasis\/Chapter 3: Conformations and Stereochemistry\/Section 3.3: Stereoisomerism \u2013 chirality, stereocenters, enantiomers\" href=\"https:\/\/chem.libretexts.org\/Textbook_Maps\/Organic_Chemistry_Textbook_Maps\/Map%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)\/Chapter_03%3A_Conformations_and_Stereochemistry\/03.3%3A_Stereoisomerism_%E2%80%93_chirality%2C_stereocenters%2C_enantiomers\" rel=\"internal\"><span class=\"internal\">enantiomers<\/span><\/a>. Unlike enatiomers which <strong>are mirror images<\/strong> of each other and <strong>non-sumperimposable<\/strong>, diastereomers are <strong>not mirror images<\/strong> of each other and <strong>non-superimposable<\/strong>. Diastereomers can have different physical properties and reactivity. They have different melting points and boiling points and different densities. They have <strong>two or more<\/strong> stereocenters.<\/p>\n<div id=\"section_1\">\n<h3 class=\"editable\">Introduction<\/h3>\n<p>It is easy to mistake between diasteromers and enantiomers. For example, we have four steroisomers of 3-bromo-2-butanol. The four possible combination are SS, RR, SR and RS (Figure 5.6.1). One of the molecule is the enantiomer of its mirror image molecule and diasteromer of each of the other two molecule (SS is enantiomer of RR and diasteromer of RS and SR). SS&#8217;s mirror image is RR and they are not superimposable, so they are enantiomers. RS and SR are not mirror image of SS and are not superimposable to each other, so they are diasteromers.<\/p>\n<div style=\"width: 860px\" class=\"wp-caption aligncenter\"><a title=\"chem (1).png\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1550\/chem_(1).png?revision=1\" rel=\"internal\"><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\/05132415\/chem_1.png\" alt=\"chem (1).png\" width=\"850\" height=\"613\" \/><\/a><\/p>\n<p class=\"wp-caption-text\">Figure 1<\/p>\n<\/div>\n<\/div>\n<div id=\"section_2\">\n<h3 class=\"editable\">Diastereomers vs. Enantiomers<\/h3>\n<p>Tartaric acid, C<sub>4<\/sub>H<sub>6<\/sub>O<sub>6<\/sub><sub>,<\/sub> is an organic compound that can be found in grape, bananas, and in wine. The structures of tartaric acid itself is really interesting. Naturally, it is in the form of (R,R) stereocenters. Artificially, it can be in the meso form (R,S), which is achiral. R,R tartaric acid is enantiomer to is mirror image which is S,S tartaric acid and diasteromers to meso-tartaric acid (Figure 5.6.2).<\/p>\n<p>(R,R) and (S,S) tartaric acid have similar physical properties and reactivity. However, meso-tartaric acid have different physical properties and reactivity. For example, melting point of (R,R) &amp; (S,S) tartaric is about 170 degree Celsius, and melting point of meso-tartaric acid is about 145 degree Celsius.<\/p>\n<div style=\"width: 780px\" class=\"wp-caption aligncenter\"><a title=\"chem1 (1).bmp\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1551\/chem1_(1).bmp?revision=1\" rel=\"internal\"><img loading=\"lazy\" decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/1551\/chem1_(1).bmp?revision=1&amp;size=bestfit&amp;width=720&amp;height=567#fixme\" alt=\"chem1 (1).bmp\" width=\"770\" height=\"607\" \/><\/a><\/p>\n<p class=\"wp-caption-text\">Figure 2<\/p>\n<\/div>\n<p>We turn our attention next to molecules which have more than one stereocenter. We will start with a common four-carbon sugar called D-erythrose.<\/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\/05132418\/image126.png\" alt=\"image126.png\" width=\"211px\" height=\"123px\" \/><\/p>\n<div>\n<p>A note on sugar nomenclature: biochemists use a special system to refer to the stereochemistry of sugar molecules, employing names of historical origin in addition to the designators &#8216;<em>D<\/em>&#8216; and &#8216;<em>L<\/em>&#8216;.\u00a0 You will learn about this system if you take a biochemistry class.\u00a0 We will use the <em>D\/L<\/em> designations here to refer to different sugars, but we won&#8217;t worry about learning the system.<\/p>\n<\/div>\n<p>As you can see, <em>D<\/em>-erythrose is a chiral molecule: C<sub>2<\/sub> and C<sub>3<\/sub> are stereocenters, both of which have the <em>R<\/em> configuration. In addition, you should make a model to convince yourself that it is impossible to find a plane of symmetry through the molecule, regardless of the conformation.\u00a0 Does D-erythrose have an enantiomer?\u00a0 Of course it does \u2013 if it is a chiral molecule, it must.\u00a0 The enantiomer of erythrose is its mirror image, and is named L-erythrose (once again, you should use models to convince yourself that these mirror images of erythrose are not superimposable).<\/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\/05132420\/image128.png\" alt=\"image128.png\" width=\"442px\" height=\"185px\" \/><\/p>\n<p>Notice that both chiral centers in L-erythrose both have the <em>S<\/em> configuration.<\/p>\n<div id=\"note\">\n<p class=\"boxtitle\">Note: In a pair of enantiomers, <strong>all <\/strong>of the chiral centers are of the opposite configuration.<\/p>\n<\/div>\n<p>What happens if we draw a stereoisomer of erythrose in which the configuration is <em>S<\/em> at C<sub>2<\/sub> and <em>R<\/em> at C<sub>3<\/sub>?\u00a0 This stereoisomer, which is a sugar called D-threose, is <em>not<\/em> a mirror image of erythrose. D-threose is a <strong>diastereomer<\/strong> of both D-erythrose and L-erythrose.<\/p>\n<p><a title=\"image129.png\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/31721\/image129.png?revision=1\" rel=\"internal\"><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132422\/image129.png\" alt=\"image129.png\" width=\"550px\" height=\"341px\" \/><\/a><\/p>\n<p>The definition of diastereomers is simple: if two molecules are stereoisomers (same molecular formula, same connectivity, different arrangement of atoms in space) but are <em>not<\/em> enantiomers, then they are diastereomers by default. <em>In practical terms, this means that at least one &#8211; but not all &#8211; of the chiral centers are opposite in a pair of diastereomers.\u00a0<\/em> By definition, two molecules that are diastereomers are <em>not<\/em> mirror images of each other.<\/p>\n<p>L-threose, the enantiomer of D-threose, has the <em>R<\/em> configuration at C<sub>2<\/sub> and the <em>S<\/em> configuration at C<sub>3<\/sub>.\u00a0 L-threose is a diastereomer of both erythrose enantiomers.<\/p>\n<p>In general, a structure with <em>n<\/em> stereocenters will have 2<sup>n<\/sup> different stereoisomers. (We are not considering, for the time being, the stereochemistry of double bonds \u2013 that will come later).\u00a0\u00a0 For example, let&#8217;s consider the glucose molecule in its open-chain form (recall that many sugar molecules can exist in either an open-chain or a cyclic form). There are two enantiomers of glucose, called D-glucose and L-glucose.\u00a0 The D-enantiomer is the common sugar that our bodies use for energy. It has <em>n<\/em> = 4 stereocenters, so therefore there are 2<sup>n<\/sup> = 2<sup>4<\/sup> = 16 possible stereoisomers (including D-glucose itself).<\/p>\n<p><a title=\"image130.png\" href=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/31720\/image130.png?revision=1\" rel=\"internal\"><img decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132424\/image130.png\" alt=\"image130.png\" width=\"550px\" height=\"353px\" \/><\/a><\/p>\n<p>In L-glucose, all of the stereocenters are inverted relative to <em>D<\/em>-glucose.\u00a0 That\u00a0 leaves 14 diastereomers of D-glucose: these are molecules in which at least one, but not all, of the stereocenters are inverted relative to D-glucose.\u00a0 One of these 14 diastereomers, a sugar called <em>D<\/em>-galactose, is shown above:\u00a0 in D-galactose, one of four stereocenters is inverted relative to D-glucose. Diastereomers which differ in only one stereocenter (out of two or more)\u00a0 are called <strong>epimers<\/strong>. D-glucose and D-galactose can therefore be refered to as epimers as well as diastereomers.<\/p>\n<div style=\"margin: auto\">\n<div id=\"example\">\n<div class=\"textbox examples\">\n<h3>Example<\/h3>\n<p>Draw the structure of\u00a0L-galactose, the\u00a0enantiomer\u00a0of\u00a0D-galactose.<\/p>\n<p>Draw the structure of two more\u00a0diastereomers\u00a0of D-glucose. One should be an\u00a0epimer.<\/p>\n<dl>\n<dt><strong>Solution:<\/strong><\/dt>\n<\/dl>\n<p><img decoding=\"async\" class=\"internal default alignnone\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05132427\/5-6-1.png\" alt=\"\" width=\"451px\" height=\"425px\" \/><\/div>\n<div><\/div>\n<\/div>\n<\/div>\n<div>Erythronolide B, a precursor to the &#8216;macrocyclic&#8217; antibiotic erythromycin, has 10 stereocenters.\u00a0 It\u2019s enantiomer is that molecule in which all 10 stereocenters are inverted.<\/div>\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\/05132429\/image136.png\" alt=\"image136.png\" width=\"262px\" height=\"307px\" \/><\/p>\n<p>In total, there are 2<sup>10 <\/sup>= 1024 stereoisomers in the erythronolide B family: 1022 of these are diastereomers of the structure above, one is the enantiomer of the structure above, and the last\u00a0 <strong><em>is <\/em><\/strong>the structure above.<\/p>\n<p>We know that enantiomers have identical physical properties and equal but opposite degrees of specific rotation.\u00a0 Diastereomers, in theory at least, have different physical properties \u2013 we stipulate \u2018in theory\u2019 because sometimes the physical properties of two or more diastereomers are so similar that it is very difficult to separate them.\u00a0 In addition, the specific rotations of diastereomers are unrelated \u2013 they could be the same sign or opposite signs, and similar in magnitude or very dissimilar.<\/p>\n<\/div>\n<div id=\"section_3\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<div id=\"section_3\">\n<div id=\"s61692\">\n<div id=\"section_18\">\n<p>Determine the stereochemistry of the following molecule:<\/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\/05132431\/5.6qu.png\" alt=\"\" width=\"349\" height=\"156\" \/><\/p>\n<\/div>\n<div id=\"section_19\">\n<h3 id=\"Solutions-61692\">Solutions<\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q622472\">Show Answer<\/span><\/p>\n<div id=\"q622472\" class=\"hidden-answer\" style=\"display: none\"><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\/05132433\/5.6sol.png\" alt=\"\" width=\"331\" height=\"148\" \/><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"section_4\"><\/div>\n<\/div>\n<\/div>\n<div id=\"section_4\">\n<h3 class=\"editable\">Contributors<\/h3>\n<ul>\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 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<p>&nbsp;<\/p>\n","protected":false},"author":44985,"menu_order":6,"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-803","chapter","type-chapter","status-publish","hentry"],"part":22,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/803","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":7,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/803\/revisions"}],"predecessor-version":[{"id":2265,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/803\/revisions\/2265"}],"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\/803\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/media?parent=803"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=803"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/contributor?post=803"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/license?post=803"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}