{"id":1053,"date":"2017-10-19T14:21:23","date_gmt":"2017-10-19T14:21:23","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/?post_type=chapter&#038;p=1053"},"modified":"2017-10-19T14:21:23","modified_gmt":"2017-10-19T14:21:23","slug":"evidence-for-the-mechanism-of-electrophilic-additions-carbocation-rearrangements","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/chapter\/evidence-for-the-mechanism-of-electrophilic-additions-carbocation-rearrangements\/","title":{"raw":"Evidence for the Mechanism of Electrophilic Additions: Carbocation Rearrangements","rendered":"Evidence for the Mechanism of Electrophilic Additions: Carbocation Rearrangements"},"content":{"raw":"<div class=\"elm-header\">\r\n<div class=\"elm-header-custom\">\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 explain the \u201cunusual\u201d products formed in certain reactions in terms of the rearrangement of an intermediate carbocation.\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"elm-main-content\" class=\"elm-content-container\">\r\n<div>\r\n<div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>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>alkyl shift<\/li>\r\n \t<li>hydride shift<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<div id=\"note\">\r\n<div class=\"textbox\">\r\n<h3 class=\"boxtitle\">Study Notes<\/h3>\r\nWhenever possible, carbocations will rearrange from a less stable isomer to a more stable isomer. This rearrangement can be achieved by either a hydride shift, where a hydrogen atom migrates from one carbon atom to the next, taking a pair of electrons with it; or an alkyl shift, in which an alkyl group undergoes a similar migration, again taking a bonding pair of electrons with it. These migrations usually occur between neighbouring carbon atoms, and hence are termed 1,2-hydride shifts or 1,2-alkyl shifts.\r\n\r\n[A hydride ion consists of a proton and two electrons, that is, [H:]<sup>\u2212<\/sup>. Hydride ions exist in compounds such as sodium hydride, NaH, and calcium hydride, CaH<sub>2<\/sub>.]\r\n\r\nAn electrophilic reaction such as HX with an alkene will often yield more than one product. This is strong evidence that the mechanism includes intermediate rearrangement steps of the cation.\r\n\r\n<\/div>\r\n\r\n\r\n<\/div>\r\n<div id=\"section_1\">\r\n<h3 class=\"editable\">1,2-Hydride Shift<\/h3>\r\nA 1,2-hydride shift is a carbocation rearrangement in which a hydrogen atom in a carbocation migrates to the carbon atom bearing the\u00a0formal charge of +1 (carbon 2) from an adjacent carbon (carbon 1).\r\n\r\neg:\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\/05141359\/12hydrideshift.png\" alt=\"\" width=\"522\" height=\"105\" \/>\r\n\r\nsee also\u00a0 <a title=\"1,2-Aryl Shift\" href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Aryl_Shift\" rel=\"internal\">1,2-aryl <\/a><a title=\"1,2-Aryl Shift\" href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Aryl_Shift\" rel=\"internal\">shift<\/a>\r\n\r\n<\/div>\r\n<div id=\"section_2\">\r\n\r\n\r\n<h3 class=\"editable\">1,2-Alkyl Shift<\/h3>\r\nA 1,2-alkyl shift is a carbocation rearrangement in which an\u00a0alkyl\u00a0group migrates to the carbon atom bearing the formal charge of +1 (carbon 2) from an adjacent carbon atom (carbon 1), e.g.\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\/05141402\/12alkylshift.png\" alt=\"\" width=\"198\" height=\"111\" \/>\r\n\r\nsee also\u00a0 <a href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Hydride_Shift\" target=\"_blank\" rel=\"internal noopener\">1,2-aryl shift, hydride shift<\/a><a href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Alkyl_Shift\" target=\"_blank\" rel=\"internal noopener\">, alkyl shift<\/a>\r\n\r\n<\/div>\r\n<div id=\"section_3\">\r\n\r\n\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<div id=\"section_3\">\r\n<h3 class=\"editable\">Exercises<\/h3>\r\n<div id=\"s61712\">\r\n<div id=\"section_37\">\r\n\r\n\r\n<h4 id=\"Questions-61712\">Questions<\/h4>\r\n<strong>1.<\/strong>\r\n\r\n<span>The following reaction shows a rearrangement within the mechanism. Propose a mechanism that shows this.<\/span>\r\n\r\n<span><img class=\"internal default aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1518\/2017\/10\/05141404\/7-11qu.png\" alt=\"\" width=\"390\" height=\"110\" \/><\/span>\r\n\r\n<\/div>\r\n<div id=\"section_38\">\r\n\r\n\r\n<h4 id=\"Solutions-61712\">Solutions<\/h4>\r\n<strong>1.<\/strong>\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\/05141407\/7-11sol.png\" alt=\"\" width=\"426\" height=\"333\" \/><span style=\"background-color: #ccd7dd;color: #000000;text-align: center\">\u00a0<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n\r\n<h3 class=\"editable\">Contributors<\/h3>\r\n<\/div>\r\n<div id=\"section_4\">\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 \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\">\n<div class=\"elm-header-custom\">\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 explain the \u201cunusual\u201d products formed in certain reactions in terms of the rearrangement of an intermediate carbocation.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"elm-main-content\" class=\"elm-content-container\">\n<div>\n<div>\n<div class=\"textbox key-takeaways\">\n<h3>Key TERMS<\/h3>\n<p>Make certain that you can define, and use in context, the key terms below.<\/p>\n<ul>\n<li>alkyl shift<\/li>\n<li>hydride shift<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div id=\"note\">\n<div class=\"textbox\">\n<h3 class=\"boxtitle\">Study Notes<\/h3>\n<p>Whenever possible, carbocations will rearrange from a less stable isomer to a more stable isomer. This rearrangement can be achieved by either a hydride shift, where a hydrogen atom migrates from one carbon atom to the next, taking a pair of electrons with it; or an alkyl shift, in which an alkyl group undergoes a similar migration, again taking a bonding pair of electrons with it. These migrations usually occur between neighbouring carbon atoms, and hence are termed 1,2-hydride shifts or 1,2-alkyl shifts.<\/p>\n<p>[A hydride ion consists of a proton and two electrons, that is, [H:]<sup>\u2212<\/sup>. Hydride ions exist in compounds such as sodium hydride, NaH, and calcium hydride, CaH<sub>2<\/sub>.]<\/p>\n<p>An electrophilic reaction such as HX with an alkene will often yield more than one product. This is strong evidence that the mechanism includes intermediate rearrangement steps of the cation.<\/p>\n<\/div>\n<\/div>\n<div id=\"section_1\">\n<h3 class=\"editable\">1,2-Hydride Shift<\/h3>\n<p>A 1,2-hydride shift is a carbocation rearrangement in which a hydrogen atom in a carbocation migrates to the carbon atom bearing the\u00a0formal charge of +1 (carbon 2) from an adjacent carbon (carbon 1).<\/p>\n<p>eg:<\/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\/1518\/2017\/10\/05141359\/12hydrideshift.png\" alt=\"\" width=\"522\" height=\"105\" \/><\/p>\n<p>see also\u00a0 <a title=\"1,2-Aryl Shift\" href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Aryl_Shift\" rel=\"internal\">1,2-aryl <\/a><a title=\"1,2-Aryl Shift\" href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Aryl_Shift\" rel=\"internal\">shift<\/a><\/p>\n<\/div>\n<div id=\"section_2\">\n<h3 class=\"editable\">1,2-Alkyl Shift<\/h3>\n<p>A 1,2-alkyl shift is a carbocation rearrangement in which an\u00a0alkyl\u00a0group migrates to the carbon atom bearing the formal charge of +1 (carbon 2) from an adjacent carbon atom (carbon 1), e.g.<\/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\/1518\/2017\/10\/05141402\/12alkylshift.png\" alt=\"\" width=\"198\" height=\"111\" \/><\/p>\n<p>see also\u00a0 <a href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Hydride_Shift\" target=\"_blank\" rel=\"internal noopener\">1,2-aryl shift, hydride shift<\/a><a href=\"https:\/\/chem.libretexts.org\/Reference\/Organic_Chemistry_Glossary\/1%2C2-Alkyl_Shift\" target=\"_blank\" rel=\"internal noopener\">, alkyl shift<\/a><\/p>\n<\/div>\n<div id=\"section_3\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<div id=\"section_3\">\n<h3 class=\"editable\">Exercises<\/h3>\n<div id=\"s61712\">\n<div id=\"section_37\">\n<h4 id=\"Questions-61712\">Questions<\/h4>\n<p><strong>1.<\/strong><\/p>\n<p><span>The following reaction shows a rearrangement within the mechanism. Propose a mechanism that shows this.<\/span><\/p>\n<p><span><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\/05141404\/7-11qu.png\" alt=\"\" width=\"390\" height=\"110\" \/><\/span><\/p>\n<\/div>\n<div id=\"section_38\">\n<h4 id=\"Solutions-61712\">Solutions<\/h4>\n<p><strong>1.<\/strong><\/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\/05141407\/7-11sol.png\" alt=\"\" width=\"426\" height=\"333\" \/><span style=\"background-color: #ccd7dd;color: #000000;text-align: center\">\u00a0<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<h3 class=\"editable\">Contributors<\/h3>\n<\/div>\n<div id=\"section_4\">\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<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":12,"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-1053","chapter","type-chapter","status-publish","hentry"],"part":23,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1053","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":3,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1053\/revisions"}],"predecessor-version":[{"id":2043,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1053\/revisions\/2043"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/parts\/23"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapters\/1053\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/media?parent=1053"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=1053"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/contributor?post=1053"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-organicchemistry\/wp-json\/wp\/v2\/license?post=1053"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}