{"id":11156,"date":"2017-11-13T06:00:07","date_gmt":"2017-11-13T12:00:07","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=11156"},"modified":"2026-04-18T06:39:46","modified_gmt":"2026-04-18T11:39:46","slug":"stereochemistry-of-the-diels-alder-reaction","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2017\/11\/13\/stereochemistry-of-the-diels-alder-reaction\/","title":{"rendered":"Stereochemistry of the Diels-Alder Reaction"},"content":{"rendered":"<p><strong>Stereochemistry of the Diels-Alder Reaction<\/strong><\/p>\n<ul>\n<li>The Diels-Alder reaction always has the same pattern of bonds that form and break. Three pi bonds are broken, and two sigma bonds (and a pi bond) are formed. The result is a new six-membered ring.<\/li>\n<li>But how does the stereochemistry of the starting diene and dienophile translate into the stereochemistry around the new six-membered ring?<\/li>\n<li>The Diels-Alder reaction is\u00a0<strong>stereospecific.\u00a0<\/strong><\/li>\n<li>Substituents that are\u00a0<strong>cis<\/strong> (trans) on the dienophile will be <strong>cis<\/strong> (trans) on the new six-membered ring.<\/li>\n<li>The two substituents on the <strong>&#8220;outside&#8221;\u00a0<\/strong>of the diene <span style=\"color: #808080;\"><em>(in the s-cis conformation)\u00a0<\/em><\/span>will end up\u00a0<strong>cis\u00a0<\/strong>on the new six-membered ring, as will the two substituents on the &#8220;<strong>inside&#8221;\u00a0<\/strong>of the diene.<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-39308\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2025\/02\/0-stereochemistry-of-the-diene-and-dienophile-in-the-diels-alder-reaction-summary-fix.gif\" alt=\"stereochemistry of the diene and dienophile in the diels alder reaction summary-fix\" width=\"640\" height=\"720\" \/><\/a><\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li><a href=\"#one\">Stereochemistry In\u00a0 The Diels-Alder: A Tale of Two Dienophiles (<em>cis<\/em>&#8211; and\u00a0<em>trans<\/em>-)<\/a><\/li>\n<li><a href=\"#two\">The Relationship Of The Substitutents About The Double Bond In The Dienophile Is Preserved In The Diels-Alder Product<\/a><\/li>\n<li><a href=\"#three\">Stereochemistry of The Diene Substituents In The Diels-Alder Product: &#8220;Outside&#8221; And &#8220;Inside&#8221; Substituents<\/a><\/li>\n<li><a href=\"#four\">Applying The &#8220;Outside \/ Inside&#8221; Rule For Dienes<\/a><\/li>\n<li><a href=\"#five\">What Happens When Both the Diene and Dienophile Are Substituted?<\/a><\/li>\n<li><a href=\"#six\">When Substituted Dienes React With Substituted Dienophiles, Diastereomers May Also Be Formed (Note: We\u00a0 Call These &#8220;Exo&#8221; and &#8220;Endo&#8221;)<\/a><\/li>\n<li><a href=\"#seven\"><i>Endo<\/i> And <i>Exo<\/i> Diels-Alder Products Are Diastereomers<\/a><\/li>\n<li><a href=\"#eight\">Summary: Stereochemistry of the\u00a0 Diels-Alder Reaction<\/a><\/li>\n<li><a href=\"#notes\">Notes<\/a><\/li>\n<li><a href=\"#quizzes\">Quiz Yourself!<\/a><\/li>\n<\/ol>\n<hr \/>\n<h2><strong><a id=\"one\"><\/a>1. Stereochemistry In\u00a0 The Diels-Alder: A Tale of Two Dienophiles (<em>cis<\/em>&#8211; and\u00a0<em>trans<\/em>-)<\/strong><\/h2>\n<p>Here&#8217;s what we&#8217;ve learned about the Diels Alder reaction so far: [<a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/09\/08\/cyclic-dienes-and-dienophiles-in-the-diels-alder-reaction\/\">previous post in this series<\/a>]<\/p>\n<ul>\n<li>3 pi bonds are always broken<\/li>\n<li>2 sigma bonds and a pi bond are always formed, resulting in a new six-membered ring<\/li>\n<li>electron withdrawing groups on the dienophile increase the reaction rate<\/li>\n<\/ul>\n<p><img decoding=\"async\" class=\"alignnone wp-image-15674\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/1-example-of-the-diels-alder-reaction-key-pattern-bonds-formed-bonds-broken-3-pi-bonds-broken-.gif\" alt=\"example of the diels alder reaction key pattern bonds formed bonds broken 3 pi bonds broken\" width=\"600\" height=\"344\" \/><\/p>\n<p>One factor we haven&#8217;t addressed yet?\u00a0<strong> Stereochemistry.<\/strong><\/p>\n<p>Let&#8217;s get started!<\/p>\n<p>A pi bond is broken on the dienophile during the course of the Diels-Alder reaction, and the hybridization goes from sp<sup>2<\/sup> to sp<sup>3<\/sup>. So what happens to the stereochemistry of the groups attached the pi bond?<\/p>\n<p>Take the two dienophiles maleic acid and fumaric acid for example. These two molecules are <em>diastereomers<\/em>, differing only in the orientation of the two carboxylic acid groups about the double bond.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-15667\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/2-good-probe-for-determining-stereochemistry-of-diels-alder-reaction-is-cis-and-trans-dienophiles-maleic-acid-and-fumaric-acid-how-does-stereochemistry-translate.gif\" alt=\"good probe for determining stereochemistry of diels alder reaction is cis and trans dienophiles maleic acid and fumaric acid how does stereochemistry translate\" width=\"600\" height=\"308\" \/><\/p>\n<p>This pair of diastereomers makes an excellent probe for determining how the stereochemistry of the dienophile pi bond is affected in the Diels-Alder reaction.<\/p>\n<p>Will the\u00a0<em>cis<\/em> carboxylic acids of maleic acid remain\u00a0<em>cis<\/em> in the product? Will the\u00a0<em>trans<\/em> carboxylic acids of fumaric acid remain\u00a0<em>trans\u00a0<\/em>in the product? Or does something else happen?<\/p>\n<p>Here&#8217;s what experiments show us:<\/p>\n<h2><strong><a id=\"two\"><\/a>2. The Relationship Of The Substitutents About The Double Bond In The Dienophile Is Preserved In The Diels-Alder Product<\/strong><\/h2>\n<p>Let&#8217;s call this Diels-Alder Stereochemistry Rule #1:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15672\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/3-diels-alder-stereochemistry-rule-1-for-substituted-dienophlies-stereochemistry-about-double-bond-in-dienophile-is-preserved-.gif\" alt=\"diels alder stereochemistry rule 1 for substituted dienophlies stereochemistry about double bond in dienophile is preserved\" width=\"600\" height=\"518\" \/><\/p>\n<p><em>cis<\/em>&#8211; dienophiles give us\u00a0<em>cis-\u00a0<\/em>products, and\u00a0<em>trans<\/em>&#8211; dienophiles give us\u00a0<em>trans-\u00a0<\/em>products.<\/p>\n<p>This is an example of a\u00a0<strong>stereospecific\u00a0<\/strong>reaction.<\/p>\n<p>A <strong>stereospecific<\/strong> reaction is one where two compounds differing only in their configuration are converted into\u00a0<strong>stereoisomeric\u00a0<\/strong>products. (see <a href=\"https:\/\/goldbook.iupac.org\/terms\/view\/S05994\">IUPAC<\/a> for the full reference).<\/p>\n<p>The\u00a0<em>cis<\/em>&#8211; and\u00a0<em>trans<\/em>&#8211; dienophiles shown here (maleic and fumaric acid, respectively) are converted into two compounds that are stereoisomers of each other.<\/p>\n<p>What about the diene?<\/p>\n<h2><a id=\"three\"><\/a>3. Stereochemistry of The Diene Substituents In The Diels-Alder Product: &#8220;Outside&#8221; And &#8220;Inside&#8221; Substituents<\/h2>\n<p>Substituents on C-2 and C-3 of the diene aren&#8217;t an issue: they start the reaction on a (flat) sp<sup>2<\/sup> hybridized carbon and end the reaction on a (flat) sp<sup>2<\/sup> hybridized carbon. No chiral centers are created here, so there&#8217;s no stereochemistry issues to concern ourselves with.<\/p>\n<p>But what about the substituents on C-1 and C-4? They are on an sp<sup>2<\/sup> hybridized carbon in the starting material and end up on an sp<sup>3<\/sup> hybridized carbon in the product.<\/p>\n<p>Here&#8217;s what we observe from experiment:<\/p>\n<p>It turns out that the two &#8220;outside groups&#8221; on the diene (labelled &#8220;<strong>A<\/strong>&#8220;, below) when drawn in the<a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/05\/12\/s-cis-and-s-trans\/\">\u00a0<em>s<\/em>-cis conformation<\/a> end up on <strong>one<\/strong> face of the new six-membered ring, and the two &#8220;inside&#8221; groups (labelled &#8220;<strong>B<\/strong>&#8220;)\u00a0 both end up on the other face of the ring. Let&#8217;s call this <strong>Diels-Alder Stereochemistry Rule #2.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15668\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/4-diels-alder-stereochemistry-rule-for-substituted-dienes-outside-groups-end-up-on-one-face-and-inside-groups-end-up-on-opposite-face.gif\" alt=\"diels alder stereochemistry rule for substituted dienes outside groups end up on one face and inside groups end up on opposite face\" width=\"600\" height=\"317\" \/><\/p>\n<p>For example, let&#8217;s examine two isomers of 2,4 hexadiene: (<em>E, E<\/em>) [example 1] and (<em>E, Z<\/em>) [example 2].<\/p>\n<h2><a id=\"four\"><\/a>4. Applying The &#8220;Outside \/ Inside&#8221; Rule For Dienes<\/h2>\n<p>Drawing each diene in the\u00a0<a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/05\/12\/s-cis-and-s-trans\/\"><em>s<\/em>&#8211;<em>cis<\/em> conformation<\/a>, which is necessary for the Diels-Alder to proceed, we see that the two &#8220;outside&#8221; groups end up on the same face of the six-membered ring, and the two &#8220;inside&#8221; groups also end up on the same face of the six-membered ring.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15669\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/5-applying-rule-with-3-3-2-4-hexadiene-shwoing-outside-groups-on-same-face-and-inside-groups-on-same-face.gif\" alt=\"applying rule with 3 3 2 4 hexadiene shwoing outside groups on same face and inside groups on same face\" width=\"600\" height=\"392\" \/><\/p>\n<p>Actually, if we look back to one of the earliest examples of the Diels-Alder that we&#8217;ve seen, this is also true for cyclopentadiene:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15670\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/6-diels-alder-stereochemistry-rule-apply-rule-for-cyclopentadiene-with-alkene-outside-groups-on-same-side.gif\" alt=\"diels alder stereochemistry rule apply rule for cyclopentadiene with alkene outside groups on same side\" width=\"600\" height=\"179\" \/><\/p>\n<p>So far, I hope that this seems straightforward enough.<\/p>\n<p>So let&#8217;s combine these two effects, and see what happens!<\/p>\n<h2><strong><a id=\"five\"><\/a>5. What Happens When Both the Diene and Dienophile Are Substituted?<\/strong><\/h2>\n<p>If we have substitution on\u00a0<strong>both\u00a0<\/strong>the diene and dienophile, what happens?\u00a0 What do we do then?<\/p>\n<p><strong>The same thing!<\/strong>\u00a0Rule #1 and Rule #2 still hold. They hold for every single Diels-Alder reaction, actually.<\/p>\n<p>For example, here&#8217;s the case of the reaction of fumaric acid with (<em>E, E)\u00a0<\/em>2,4 hexadiene:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15673\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/7-what-happens-when-diels-alder-stereochemistry-has-substituted-diene-and-substituted-dienophile-still-apply-same-rule-preserve-stereochemistry-.gif\" alt=\"what happens when diels alder stereochemistry has substituted diene and substituted dienophile still apply same rule preserve stereochemistry\" width=\"600\" height=\"354\" \/><\/p>\n<p>This results in a single product formed as a racemic mixture of enantiomers.<\/p>\n<p>Simple?<\/p>\n<p><em>Not always.\u00a0<\/em><\/p>\n<h2><strong><a id=\"six\"><\/a>6. When Substituted Dienes React With Substituted Dienophiles, Diastereomers May Also Be Formed (Note: We\u00a0 Call These &#8220;Exo&#8221; and &#8220;Endo&#8221;)<\/strong><\/h2>\n<p>Fumaric acid has the property of being symmetrical with respect to rotation (<em>you might sometimes hear this described as <a href=\"https:\/\/en.wikipedia.org\/wiki\/Rotational_symmetry\">C2 symmetry<\/a><\/em>), which has the consequence that only one product (as a pair of\u00a0<em>enantiomers) <\/em>is\u00a0\u00a0formed in the reaction with 2,4-hexadiene.<\/p>\n<p>However, fumaric acid&#8217;s cousin, maleic acid, lacks this property.<\/p>\n<p>When we combine a substituted diene such as (<em>E, E<\/em>) 2,4-hexadiene with maleic acid, and follow both Rule #1 and Rule #2, there are actually\u00a0<em>two<\/em> possible products!<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15671\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/8-what-is-exo-and-endo-this-occurs-when-substituted-diene-and-substituted-dienophile-two-diastereomers-possible-endo-and-exo-endo-is-major-each-diastereomer-has-enantiomer-as-well.gif\" alt=\"what is exo and endo this occurs when substituted diene and substituted dienophile two diastereomers possible endo and exo endo is major each diastereomer has enantiomer as well\" width=\"630\" height=\"508\" \/><\/p>\n<p>In the first product, the &#8220;outside&#8221; CH<sub>3<\/sub> groups are on the same side of the new six-membered ring as the carboxylic acids in maleic acid. We call this the &#8220;endo&#8221; product.<\/p>\n<p>In the second product, the &#8220;outside&#8221; CH<sub>3<\/sub> groups are on the opposite side of the new six-membered ring as the carboxylic acids in maleic acid. We call this the &#8220;exo&#8221; product.<\/p>\n<h2><a id=\"seven\"><\/a>7. <em>Endo<\/em> And <em>Exo<\/em> Diels-Alder Products Are Diastereomers<\/h2>\n<p>The &#8220;endo&#8221; and &#8220;exo&#8221; products in this case are\u00a0<strong>diastereomers.\u00a0<\/strong>They are stereoisomers of each other, but are not enantiomers. (In fact, neither the &#8220;endo&#8221; or &#8220;exo&#8221; products in the example above possess an enantiomer. Can you see why?).<\/p>\n<p>In practice, for reasons that will not be immediately obvioius, the &#8220;endo&#8221; product tends to be favored over the &#8220;exo&#8221; product.<\/p>\n<p>This subject of exo and endo turns out to be such an important topic that it deserves its own article. So we&#8217;ll explore exactly how to tell the difference between &#8220;exo&#8221; and &#8220;endo&#8221; products, as well as how they form, in the next article.<\/p>\n<h2><a id=\"eight\"><\/a>8. Summary: Stereochemistry of the\u00a0 Diels-Alder Reaction<\/h2>\n<ul>\n<li>The stereochemistry of the dienophile is preserved\u00a0 in the Diels-Alder product<\/li>\n<li>The &#8220;outside&#8221; groups on\u00a0 the diene end up on the same face of\u00a0 the new\u00a0 six-membered ring, as\u00a0 do\u00a0 \u00a0the &#8220;inside&#8221; groups.<\/li>\n<li>When both the diene and\u00a0 dienophile are substituted, diastereomers may form, which we call &#8220;exo&#8221; and &#8220;endo&#8221;.<\/li>\n<\/ul>\n<p><strong>Thanks to Tom Struble for assistance with this post.\u00a0<\/strong><\/p>\n<hr \/>\n<h2><strong><a id=\"notes\"><\/a>Notes<\/strong><\/h2>\n<div class=\"related-articles\"><p><strong>Related Articles<\/strong><\/p><ul><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/09\/10\/types-of-isomers\/\" class=\"\"><span>Types of Isomers: Constitutional Isomers, Stereoisomers, Enantiomers, and Diastereomers<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/02\/09\/endo-exo-diels-alder-telling-them-apart\/\" class=\"\"><span>Exo vs Endo Products In The Diels Alder: How To Tell Them Apart<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/05\/11\/endo-vs-exo-in-the-diels-alder-reaction\/\" class=\"\"><span>Why Are Endo vs Exo Products Favored in the Diels-Alder Reaction?<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/03\/23\/molecular-orbitals-in-the-diels-alder-reaction\/\" class=\"\"><span>HOMO and LUMO In the Diels Alder Reaction<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/08\/30\/the-diels-alder-reaction\/\" class=\"\"><span>The Diels-Alder Reaction<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2019\/03\/08\/enantiomers-diastereomers-or-the-same-1-using-models\/\" class=\"\"><span>Enantiomers vs Diastereomers vs The Same? Two Methods For Solving Problems<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/05\/12\/s-cis-and-s-trans\/\" class=\"\"><span>s-cis and s-trans<\/span><\/a><\/li><\/ul><\/div>\n<p><strong><a id=\"noteone\"><\/a>Note 1. <\/strong>The Diels-Alder reaction of (E,E) 2,4 hexadiene with fumaric acid produced a pair of enantiomers, but neither of the products of the Diels-Alder of (E,E)-2,4-hexadiene with maleic acid has an enantiomer. Can you see why?<\/p>\n<hr \/>\n<h2><a id=\"quizzes\"><\/a>Quiz Yourself!<\/h2>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0045-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/1708-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/1713-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3082-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3083-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3084-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Stereochemistry of the Diels-Alder Reaction The Diels-Alder reaction always has the same pattern of bonds that form and break. Three pi bonds are broken, and <\/p>\n","protected":false},"author":1,"featured_media":39308,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1163],"tags":[631,1287,1288,1206,273],"post_folder":[],"class_list":["post-11156","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dienes-and-mo-theory","tag-diels-alder","tag-endo","tag-exo","tag-s-cis","tag-stereochemistry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Stereochemistry of the Diels-Alder Reaction &#8211; Master Organic Chemistry<\/title>\n<meta name=\"description\" content=\"When the diene or dienophile is substituted, what&#039;s the stereochemistry of the Diels-Alder product? 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