{"id":5034,"date":"2020-06-07T05:41:12","date_gmt":"2020-06-07T05:41:12","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/?post_type=chapter&#038;p=5034"},"modified":"2021-02-15T07:53:58","modified_gmt":"2021-02-15T07:53:58","slug":"10-8-anti-markovnikov-additions-to-alkenes-and-alkynes","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/10-8-anti-markovnikov-additions-to-alkenes-and-alkynes\/","title":{"raw":"10.8. Anti-Markovnikov additions to alkenes and alkynes","rendered":"10.8. Anti-Markovnikov additions to alkenes and alkynes"},"content":{"raw":"<header><\/header>\r\n<h1>10.8.1. Anti-Markovnikov addition of HBr to alkenes<\/h1>\r\n<section>We saw in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/10-4-simple-addition-to-alkenes\/\">section 10.4<\/a> that under normal conditions, HBr adds to an unsymmetrical alkene to form an alkyl halide where the H goes onto the less substituted carbon, and the Br goes onto the more substituted carbon - thus, it obeys Markovnikov's Rule.\u00a0 However, when heated in the presence of a dialkyl peroxide (often written as ROOR), a radical mechanism takes over and a product is formed the opposite way round - due to the so-called \"peroxide effect\".\u00a0 This \"anti-Markovnikov product\" has the H placed onto the more substituted carbon, and the Br on the less substituted carbon.\u00a0<\/section><section><\/section><section><img class=\"alignnone wp-image-5041\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/08025020\/HBrAdditionMvAndAntiMv.png\" alt=\"Simple HBr adds to propene to form 2-bromopropane, but in presence of HBr\/ROOR it forms 1-bromopropane\" width=\"465\" height=\"174\" \/><\/section><section>This is useful in synthesis, because both products are accessible in one step from one alkene.<\/section><section><\/section><section>The mechanism in the presence of peroxides involves free radicals, and will be covered in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/\">part 2 of this book<\/a>.<\/section><section><\/section><section><\/section><section><\/section>\r\n<h1>10.8.2. Anti-Markovnikov addition of H<sub>2<\/sub>O to alkenes<\/h1>\r\n<section>\r\n<h2>Hydroboration-oxidation<\/h2>\r\n<\/section><section>\r\n<div>\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nAfter completing this section, you should be able to\r\n<ol>\r\n \t<li>identify hydroboration (followed by oxidation) as a method for bringing about the (apparently) non-Markovnikov addition of water to an alkene.<\/li>\r\n \t<li>Write an equation for the formation of a trialkylborane from an alkene and borane.<\/li>\r\n \t<li>Erite an equation for the oxidation of a trialkylborane to an alcohol.<\/li>\r\n \t<li>Draw the structure of the alcohol produced by the hydroboration, and subsequent oxidation, of a given alkene.<\/li>\r\n \t<li>Determine whether a given alcohol should be prepared by oxymercuration-demercuration or by hydroboration-oxidation, and identify the alkene and reagents required to carry out such a synthesis.<\/li>\r\n \t<li>Write the detailed mechanism for the addition of borane to an alkene, and explain the stereochemistry and regiochemistry of the reaction.<\/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\nMake certain that you can define, and use in context, the key term below.\r\n<ul>\r\n \t<li>hydroboration<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<h3>Study Notes<\/h3>\r\nThe two most important factors influencing organic reactions are polar (or electronic) effects and steric effects.\u00a0 This reaction exhibits both factors.\u00a0 Since boron is both larger and less electronegative than hydrogen, when BH<sub>3<\/sub> adds to an alkene we see the hydrogen go onto the <em>more<\/em> substituted carbon.\u00a0 This is the opposite of what we have usually seen with most additions of H-X, because in previous examples the X atom (Cl, Br, I, or O) was always <em>more<\/em> electronegative than H.\r\n\r\n<\/div>\r\nHydroboration-oxidation is a two step pathway used\u00a0to produce\u00a0alcohols. The reaction proceeds in an <a href=\"\/Organic_Chemistry\/Hydrocarbons\/Alkenes\/Reactions_of_Alkenes\/Radical_Additions--Anti-Markovnikov_Product_Formation\">anti-Markovnikov<\/a> manner, where the\u00a0hydrogen (from BH<sub>3<\/sub> or BHR<sub>2<\/sub>) attaches to the more substituted carbon and the boron\u00a0attaches to the\u00a0least substituted carbon in the <a href=\"\/Organic_Chemistry\/Hydrocarbons\/Alkenes\">alkene<\/a> double bond. Furthermore, the borane acts as a Lewis acid by\u00a0accepting two electrons in its empty p\u00a0orbital\u00a0from\u00a0an alkene that is electron rich. This process allows boron to have\u00a0an complete octet.\u00a0 The hydroboration mechanism\u00a0has\u00a0the elements of both hydrogenation and <a href=\"\/Organic_Chemistry\/Conjugation\/Electrophilic_Attack_on_Conjugated_Dienes\/Electrophile\">electrophilic<\/a> addition\u00a0and it is\u00a0a stereospecific\u00a0(<strong><em>syn addition),<\/em><\/strong> meaning that the\u00a0hydroboration takes place on the same\u00a0face of the double bond, this leads <em><strong>cis<\/strong><\/em> stereochemistry.\r\n<div>\r\n<div>\r\n<h3>Introduction<\/h3>\r\nHydroboration-oxidation of alkenes has been a very valuable laboratory method for the stereoselective and regioselective addition of alkenes, without any rearrangement.\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n<h3>The borane complex<\/h3>\r\nBorane itself exists naturally as a very toxic gas in the form of a dimer with the general formula B<sub>2<\/sub>H<sub>6<\/sub> (diborane), which ignites spontaneously in air. Borane is commercially available in ether and tetrahydrofuran (THF).\u00a0 In these solutions the borane exists as a Lewis acid-base complex, which allows boron to have an complete octet.<img class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2058\/THF.bmp?revision=1&amp;size=bestfit&amp;width=451&amp;height=122#fixme#fixme\" alt=\"THF.bmp\" width=\"451\" height=\"122\" \/>\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n<h3>The mechanism<\/h3>\r\n<div>\r\n<div>\r\n<h4><strong>Elementary step #1<\/strong><\/h4>\r\nPart #1: Hydroboration of the alkene. In this first step the addition of the borane to the alkene is initiated and proceeds as a concerted reaction because bond breaking and bond formation occur at the same time. This step involves the vacant 2p orbital of the boron electrophile pairing with the electron pair of the\u00a0\u03c0-bond of the alkene nucleophile.\r\n\r\n<img class=\"wp-image-5077 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21042655\/HydroborationMechanism.png\" alt=\"The B-H bond adds across the double bond of an alkene in one step\" width=\"684\" height=\"101\" \/>\r\n\r\n&nbsp;\r\n<ul>\r\n \t<li>In the product, the boron has added to the less substituted carbon of the alkene, which then places the hydrogen on the more substituted carbon. Both, the boron and the hydrogen add simultaneously on the same face of the double bond (syn addition).<\/li>\r\n \t<li>Note that a carbocation is not formed. Therefore, no rearrangement takes place.<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n<h3>Oxidation of the trialkylborane by hydrogen peroxide<\/h3>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n\r\nYou will not be required to know this part of the mechanism for this course, but further information is available in the links below.\r\n<h3>Stereochemistry of hydroboration<\/h3>\r\nThe hydroboration reaction is among the few simple addition reactions that proceed cleanly in a <em>syn <\/em>fashion, <em>i.e.<\/em>, the boron and the hydrogen end up on the same side. As noted above, this is a single-step reaction. Since the bonding of the double bond carbons to boron and hydrogen is concerted, it follows that the geometry of this addition must be <em>syn<\/em>. Furthermore, rearrangements are unlikely inasmuch as a discrete carbocation intermediate is never formed.\r\n\r\nSince the hydroboration procedure is most commonly used to hydrate alkenes in an anti-Markovnikov fashion, we also need to know the stereoselectivity of the second oxidation reaction, which substitutes a hydroxyl group for the boron atom. Independent study has shown this reaction takes place with retention of configuration so the overall addition of water is also <em>syn<\/em>.\r\n\r\n<\/div>\r\n<div>\r\n<div class=\"textbox examples\">\r\n<h3>Further Readings<\/h3>\r\n<ul>\r\n \t<li><a href=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\" target=\"_blank\" rel=\"noopener\">http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation<\/a><\/li>\r\n<\/ul>\r\n<img class=\"size-thumbnail wp-image-4694 alignnone\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2018\/08\/01191827\/static_qr_code_without_logo5-150x150.png\" alt=\"\" width=\"150\" height=\"150\" \/>\r\n<ul>\r\n \t<li><a href=\"http:\/\/www.chemhelper.com\/hydroboration.html\" target=\"_blank\" rel=\"noopener\">http:\/\/www.chemhelper.com\/hydroboration.html<\/a><\/li>\r\n<\/ul>\r\n<img class=\"size-thumbnail wp-image-4695 alignnone\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2018\/08\/01192007\/static_qr_code_without_logo3-150x150.png\" alt=\"\" width=\"150\" height=\"150\" \/>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n<h3>References<\/h3>\r\n<ol>\r\n \t<li>Vollhardt, Peter, and Neil Shore.\u00a0Organic Chemistry: Structure and Function. 5th. New York: W.H. Freeman and Company, 2007.<\/li>\r\n \t<li>Foote, S. Christopher, and William H. Brown. Organic Chemistry. 5th. Belmont, CA: Brooks\/Cole Cengage Learning, 2005.<\/li>\r\n \t<li>Bruice, Paula Yurkanis. Oragnic Chemistry. 5th. CA. Prentice Hall, 2006.<\/li>\r\n \t<li>Bergbreiter E. David , and David P. Rainville. Stereochemistry of hydroboration-oxidation of terminal alkenes.\u00a0J. Org. Chem., 1976, 41 (18), pp 3031\u20133033<\/li>\r\n \t<li>Ilich, Predrag-Peter; Rickertsen, Lucas S., and Becker Erienne. Polar Addition to C=C Group: Why Is Anti-Markovnikov Hydroboration-Oxidation of Alkenes Not \"Anti-\"? Journal of Chemical Education., 2006, v83, n11, pg 1681-1685<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n<div>\r\n<div>\r\n<div>\r\n<div>\r\n<div>\r\n<div class=\"textbox exercises\">\r\n<h3>Problems<\/h3>\r\n<div>\r\n<div>\r\n\r\n<strong>What are the products of these following reactions? <\/strong>\r\n\r\n<strong>#1.<\/strong>\r\n\r\n<strong><img class=\"wp-image-5078 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21132457\/HydroborationQ1.png\" alt=\"BH3 adds to 1-methylcyclohexene to give..?\" width=\"248\" height=\"95\" \/><\/strong>\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n<strong>#2.<\/strong>\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n\r\n<img class=\"wp-image-5079 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21133542\/HydroborationQ2.png\" alt=\"What is hydroboration-oxidation product from (E)-3-methylpent-2-ene\" width=\"345\" height=\"90\" \/>\r\n\r\n<strong>#3.<\/strong>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"wp-image-5080 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21134006\/HydroborationQ3.png\" alt=\"What is hydroboration-oxidation product of 2-methylprop-1-enylcyclohexane?\" width=\"329\" height=\"82\" \/>\r\n\r\n&nbsp;\r\n\r\n<strong>Draw the structural formulas for the alcohols that result from hydroboration-oxidation of the alkenes shown.<\/strong>\r\n\r\n<strong>#4.<\/strong>\r\n\r\n<img class=\"wp-image-5081 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21134224\/HydroborationQ4.png\" alt=\"What is the hydroboration-oxidation product from 2-methylbut-2-ene?\" width=\"293\" height=\"86\" \/>\r\n\r\n<strong>#5. (E)-3-methyl-2-pentene\u00a0 <\/strong>\r\n\r\nIf you need a reminder, see the <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/3-2-nomenclature-of-unsaturated-hydrocarbons\/\">section on naming alkenes<\/a>.\r\n\r\n&nbsp;\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<div>\r\n<h3><strong>Answers<\/strong><\/h3>\r\n[reveal-answer q=\"433977\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"433977\"]\r\n\r\n<strong>#1.<\/strong>\r\n\r\n<img class=\"wp-image-5083 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21144408\/HydroborationA1.png\" alt=\"trans-2-methylcyclohexylborane\" width=\"207\" height=\"86\" \/><strong>#2.<\/strong>\r\n\r\n<img class=\"wp-image-5084 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21144703\/HydroborationA2.png\" alt=\"Racemic (2S,3R)-3-methylhexan-2-ol\" width=\"208\" height=\"85\" \/>\r\n\r\n<strong>#3. <\/strong>\r\n\r\n<img class=\"wp-image-5085 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21145946\/HydroborationA3.png\" alt=\"Racemic 1-cyclohexyl-2-methyl-propan-1-ol\" width=\"211\" height=\"99\" \/>\r\n\r\n<strong>#4.<\/strong>\r\n\r\n<img class=\"wp-image-5086 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21150217\/HydroborationA4.png\" alt=\"Racemic 3-methylbutan-2-ol\" width=\"184\" height=\"102\" \/>\r\n\r\n<strong>#5.<\/strong>\r\n\r\n<img class=\"wp-image-5087 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21150338\/HydroborationA5.png\" alt=\"Racemic 3-methylpentan-2-ol\" width=\"207\" height=\"101\" \/>\r\n\r\n<\/div>\r\n&nbsp;\r\n<div>\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<div>\r\n<div>\r\n<div>\r\n\r\nWrite out the reagents or products (A\u2013D) shown in the following reaction schemes.\r\n\r\n<img class=\"wp-image-5074 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/20030555\/HydroborationQAnswers01a.png\" alt=\"Hydration reactions of 1-methylcyclopentene and 2-methylbut-1-ene\" width=\"337\" height=\"366\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<h3>Solutions<\/h3>\r\n[reveal-answer q=\"652262\"]Show Solution[\/reveal-answer]\r\n\r\n<img class=\"wp-image-5073 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/20025354\/HydroborationQAnswers01b.png\" alt=\"Answers to questions on hydration of alkenes\" width=\"323\" height=\"328\" \/>\r\n[hidden-answer a=\"652262\"][\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/section>\r\n<h1>10.8.3. Anti-Markovnikov addition of HBr to alkynes<\/h1>\r\n<section class=\"mt-content-container\">Most hydrogen halide reactions with alkynes occur in a Markovnikov-manner in which the halide attaches to the most substituted carbon since it is the most positively polarized. A more substituted carbon has more bonds attached to 1) carbons or 2) electron-donating groups such as Fluorine and other halides. However, there are two specific reactions among alkynes where anti-Markovnikov reactions take place: the radical addition of HBr and hydroboration-oxidation reactions. For alkynes, an anti-Markovnikov addition takes place on a terminal alkyne, an alkyne on the end of a chain.\r\n<div id=\"section_1\" class=\"mt-section\">\r\n<h2 class=\"editable\">HBr Addition With Radical Yields 1-bromoalkene<\/h2>\r\nThe Br of the Hydrogen Bromide (H-Br) attaches to the less substituted 1-carbon of the terminal alkyne shown below in an anti-Markovnikov manner while the Hydrogen proton attaches to the second carbon. As mentioned above, the first carbon is the less substituted carbon since it has fewer bonds attached to carbons and other substituents. The H-Br reagent must also be reacted with heat or some other radicial initiator such as a peroxide in order for this reaction to proceed in this manner. This presence of the radical or heat leads to the anti-Markovnikov addition since it produces the most stable reaction.\u00a0 The mechanism for this reaction will be covered later.\r\n\r\n<img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2192\/hbr_(1).JPG?revision=1&amp;size=bestfit&amp;width=550&amp;height=132\" alt=\"hbr (1).JPG\" width=\"550px\" height=\"132px\" \/>\r\n\r\nThe product of a terminal alkyne that is reacted with a peroxide (or light) and H-Br is a 1-bromoalkene.\r\n\r\n<strong>Regioselectivity<\/strong>: The Bromine can attach in a <strong><em>syn <\/em><\/strong>or <strong><em>anti <\/em><\/strong>manner which means the resulting alkene can be both <strong><em>cis <\/em><\/strong>and<strong> <em>tran<\/em><em>s<\/em><\/strong>. <strong><em>Syn <\/em><\/strong>addition is when both Hydrogens attach to the same face or side of the double bond (i.e. <strong><em>cis<\/em><\/strong>) while the <strong><em>anti<\/em><\/strong> addition is when they attach on opposite sides of the bond (<strong><em>trans<\/em><\/strong>).\r\n\r\n<\/div>\r\n<div id=\"section_2\" class=\"mt-section\">\r\n<h1>10.8.4. Anti-Markovnikov addition of H<sub>2<\/sub>O to alkynes<\/h1>\r\n<h2 class=\"editable\">Stereospecific Hydroboration Oxidation of Alkynes<\/h2>\r\nBoranes such as dicyclohexylborane react with alkynes to give aldehydes, after oxidation of the intermediate borane.\r\n\r\n<img class=\" wp-image-5164 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/15075007\/Cy2BH_Alkyne_HydroborationOxidationOverall.png\" alt=\"Pent-1-yne is converted to pentanal using Cy2BH then alkaline H2O2\" width=\"432\" height=\"90\" \/>\r\n\r\n<strong>Step 1:<\/strong> Hydroboration of terminal alkynes reacts in an anti-Markovnikov fashion in which the boron attacks the less substituted carbon which is the least hindered. It is a stereospecific reaction where <strong><em>syn <\/em><\/strong>addition is observed as the hydroboration occurs on the same side of the alkyne and results in <strong><em>cis <\/em><\/strong>stereochemistry. However, a bulky borane reagent needs to be used to stop at the addition the alkenyl-borane stage. Otherwise, a second hydroboration will occur. Common sterically hindered borane reagents include dicyclohexylborane (written as Cy<sub>2<\/sub>BH) and diisoamyl borane (written as Sia<sub>2<\/sub>BH).\r\n\r\n<img class=\"size-full wp-image-5158 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/15072229\/Cy2BH_Alkyne_Hydroboration.png\" alt=\"Hydroboration of pent-1-yne to form an alkenylborane\" width=\"432\" height=\"91\" \/>\r\n\r\n<strong>Step 2:<\/strong> Oxidation is the next step that occurs. The resulting alkenylborane is oxidized to an enol due to the reaction with hydrogen peroxide in a basic solution such as aqueous sodium hydroxide. As we saw in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/10-5-simple-addition-to-alkynes\/\">section 10.5<\/a>, an enol will go rapid tautomerization and rearrange into a carbonyl (C=O) compound as the product - in this case, in basic solution.\r\n\r\n<img class=\" wp-image-5160 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/15073831\/Cy2BH_Alkyne_OxidationStep1.png\" alt=\"Oxidation of an alkenylborane to an enol, then tautomerization to pentanal\" width=\"677\" height=\"94\" \/>\r\n\r\n<\/div>\r\n<div id=\"section_2\" class=\"mt-section\">\r\n\r\nFor additional information on hydroboration oxidation: See <a href=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\">Hydroboration-oxidation<\/a> in Wikipedia\r\n\r\n<\/div>\r\n<div id=\"section_3\" class=\"mt-section\">\r\n<h2 class=\"editable\">References<\/h2>\r\n<ol>\r\n \t<li>Brown, Herbert C. <u>Hydroboration With Supplement<\/u>. New York: Addison-Wesley Pub Co, 1980.<\/li>\r\n \t<li>Dhillon, Ranjit S. <u>Hydroboration and Organic Synthesis 9-Borabicyclo [3.3.1] nonane (9-BBN)<\/u>. New York: Springer, 2007.<\/li>\r\n \t<li>Minkin, V. I. <u>Molecular design of tautomeric compounds<\/u>. Dordrecht: D. Reidel Pub. Co., U.S.A. and Canada, 1988.<\/li>\r\n \t<li>Vollhardt, K. Peter C., and Neil E. Schore. <u>Organic Chemistry Structure and Function<\/u>. New York: W. H. Freeman, 2005.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"section_4\" class=\"mt-section\">\r\n\r\n&nbsp;\r\n<h2 class=\"editable\">Outside Links<\/h2>\r\n<ul>\r\n \t<li><a class=\"external\" title=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\" href=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\" target=\"_blank\" rel=\"external nofollow noopener\">http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation<\/a><\/li>\r\n \t<li>Markovnikov's Rule: <a class=\"external\" title=\"http:\/\/en.wikipedia.org\/wiki\/Markovnikov%27s_rule\" href=\"http:\/\/en.wikipedia.org\/wiki\/Markovnikov%27s_rule\" target=\"_blank\" rel=\"external nofollow noopener\">http:\/\/en.wikipedia.org\/wiki\/Markovnikov%27s_rule<\/a><\/li>\r\n \t<li>For more on alkynes: <cite>www.ulm.edu\/~junk\/examkeys\/pp230_7_ch8.ppt<\/cite><\/li>\r\n<\/ul>\r\n<\/div>\r\n<div id=\"section_5\" class=\"mt-section\">\r\n\r\n&nbsp;\r\n<h2 class=\"editable\">Problems<\/h2>\r\n1. What is the product of this reaction?\r\n\r\n<img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2197\/wikiproblem_(3).jpg?revision=1&amp;size=bestfit&amp;width=591&amp;height=243\" alt=\"wikiproblem (3).jpg\" width=\"591px\" height=\"243px\" \/>\r\n\r\n2. What process causes the conversion of a vinyl alcohol to an aldeyde and what are some of its distinct features?\r\n\r\n3. True or False: Only <em>cis <\/em>products are observed in radical H-Br additions to terminal alkynes.\r\n\r\n4. Explain why a bulky borane reagent is necessary for hydroboration oxidation reactions.\r\n\r\n5. Draw the product.\r\n\r\n<\/div>\r\n<div id=\"section_6\" class=\"mt-section\">\r\n<h2 class=\"editable\"><img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2194\/Problem_2.jpg?revision=1&amp;size=bestfit&amp;width=480&amp;height=194\" alt=\"Problem 2.jpg\" width=\"480px\" height=\"194px\" \/><\/h2>\r\n<\/div>\r\n<div id=\"section_7\" class=\"mt-section\">\r\n\r\n&nbsp;\r\n<h2 class=\"editable\">Answers<\/h2>\r\n1. Don't be confused by the borane reagent! Just remember, anytime there is a bulky borane reagent reacting with a terminal alkyne, the hydroboration oxidation reaction will occur and be proceeded by tautomerism which will produce an aldeyde as shown below.\r\n\r\n<img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2196\/wikianswer.jpg?revision=1&amp;size=bestfit&amp;width=472&amp;height=190\" alt=\"wikianswer.jpg\" width=\"472px\" height=\"190px\" \/>\r\n\r\n2. The interconversion of an enol or vinyl alcohol to an aldehyde is called tautomerism and it is very distinct since it is a spontaneous reaction that proceeds very quickly.\r\n\r\n3. False. Both <em>cis <\/em>and <em>trans<\/em> products are produced as both <em>syn <\/em>and <em>anti<\/em> additions are observed.\r\n\r\n4. If a small borane reagent is utilized, both pi bonds will be used and a second hydroboration will occur. This will break the double bond of the alkene and the aldehyde product will not be formed.\r\n\r\n5.\r\n\r\n<img class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2193\/Problem_2_answer.jpg?revision=1&amp;size=bestfit&amp;width=169&amp;height=163\" alt=\"Problem 2 answer.jpg\" width=\"169px\" height=\"163px\" \/>\r\n\r\n<\/div>\r\n<div id=\"section_8\" class=\"mt-section\">\r\n\r\n&nbsp;\r\n<h2 class=\"editable\">Contributors<\/h2>\r\n<ul>\r\n \t<li>Ali Alvandi<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/section>","rendered":"<header><\/header>\n<h1>10.8.1. Anti-Markovnikov addition of HBr to alkenes<\/h1>\n<section>We saw in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/10-4-simple-addition-to-alkenes\/\">section 10.4<\/a> that under normal conditions, HBr adds to an unsymmetrical alkene to form an alkyl halide where the H goes onto the less substituted carbon, and the Br goes onto the more substituted carbon &#8211; thus, it obeys Markovnikov&#8217;s Rule.\u00a0 However, when heated in the presence of a dialkyl peroxide (often written as ROOR), a radical mechanism takes over and a product is formed the opposite way round &#8211; due to the so-called &#8220;peroxide effect&#8221;.\u00a0 This &#8220;anti-Markovnikov product&#8221; has the H placed onto the more substituted carbon, and the Br on the less substituted carbon.\u00a0<\/section>\n<section><\/section>\n<section><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-5041\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/08025020\/HBrAdditionMvAndAntiMv.png\" alt=\"Simple HBr adds to propene to form 2-bromopropane, but in presence of HBr\/ROOR it forms 1-bromopropane\" width=\"465\" height=\"174\" \/><\/section>\n<section>This is useful in synthesis, because both products are accessible in one step from one alkene.<\/section>\n<section><\/section>\n<section>The mechanism in the presence of peroxides involves free radicals, and will be covered in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/\">part 2 of this book<\/a>.<\/section>\n<section><\/section>\n<section><\/section>\n<section><\/section>\n<h1>10.8.2. Anti-Markovnikov addition of H<sub>2<\/sub>O to alkenes<\/h1>\n<section>\n<h2>Hydroboration-oxidation<\/h2>\n<\/section>\n<section>\n<div>\n<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>After completing this section, you should be able to<\/p>\n<ol>\n<li>identify hydroboration (followed by oxidation) as a method for bringing about the (apparently) non-Markovnikov addition of water to an alkene.<\/li>\n<li>Write an equation for the formation of a trialkylborane from an alkene and borane.<\/li>\n<li>Erite an equation for the oxidation of a trialkylborane to an alcohol.<\/li>\n<li>Draw the structure of the alcohol produced by the hydroboration, and subsequent oxidation, of a given alkene.<\/li>\n<li>Determine whether a given alcohol should be prepared by oxymercuration-demercuration or by hydroboration-oxidation, and identify the alkene and reagents required to carry out such a synthesis.<\/li>\n<li>Write the detailed mechanism for the addition of borane to an alkene, and explain the stereochemistry and regiochemistry of the reaction.<\/li>\n<\/ol>\n<\/div>\n<\/div>\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 term below.<\/p>\n<ul>\n<li>hydroboration<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<h3>Study Notes<\/h3>\n<p>The two most important factors influencing organic reactions are polar (or electronic) effects and steric effects.\u00a0 This reaction exhibits both factors.\u00a0 Since boron is both larger and less electronegative than hydrogen, when BH<sub>3<\/sub> adds to an alkene we see the hydrogen go onto the <em>more<\/em> substituted carbon.\u00a0 This is the opposite of what we have usually seen with most additions of H-X, because in previous examples the X atom (Cl, Br, I, or O) was always <em>more<\/em> electronegative than H.<\/p>\n<\/div>\n<p>Hydroboration-oxidation is a two step pathway used\u00a0to produce\u00a0alcohols. The reaction proceeds in an <a href=\"\/Organic_Chemistry\/Hydrocarbons\/Alkenes\/Reactions_of_Alkenes\/Radical_Additions--Anti-Markovnikov_Product_Formation\">anti-Markovnikov<\/a> manner, where the\u00a0hydrogen (from BH<sub>3<\/sub> or BHR<sub>2<\/sub>) attaches to the more substituted carbon and the boron\u00a0attaches to the\u00a0least substituted carbon in the <a href=\"\/Organic_Chemistry\/Hydrocarbons\/Alkenes\">alkene<\/a> double bond. Furthermore, the borane acts as a Lewis acid by\u00a0accepting two electrons in its empty p\u00a0orbital\u00a0from\u00a0an alkene that is electron rich. This process allows boron to have\u00a0an complete octet.\u00a0 The hydroboration mechanism\u00a0has\u00a0the elements of both hydrogenation and <a href=\"\/Organic_Chemistry\/Conjugation\/Electrophilic_Attack_on_Conjugated_Dienes\/Electrophile\">electrophilic<\/a> addition\u00a0and it is\u00a0a stereospecific\u00a0(<strong><em>syn addition),<\/em><\/strong> meaning that the\u00a0hydroboration takes place on the same\u00a0face of the double bond, this leads <em><strong>cis<\/strong><\/em> stereochemistry.<\/p>\n<div>\n<div>\n<h3>Introduction<\/h3>\n<p>Hydroboration-oxidation of alkenes has been a very valuable laboratory method for the stereoselective and regioselective addition of alkenes, without any rearrangement.<\/p>\n<\/div>\n<\/div>\n<div>\n<div>\n<h3>The borane complex<\/h3>\n<p>Borane itself exists naturally as a very toxic gas in the form of a dimer with the general formula B<sub>2<\/sub>H<sub>6<\/sub> (diborane), which ignites spontaneously in air. Borane is commercially available in ether and tetrahydrofuran (THF).\u00a0 In these solutions the borane exists as a Lewis acid-base complex, which allows boron to have an complete octet.<img loading=\"lazy\" decoding=\"async\" class=\"internal default aligncenter\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2058\/THF.bmp?revision=1&amp;size=bestfit&amp;width=451&amp;height=122#fixme#fixme\" alt=\"THF.bmp\" width=\"451\" height=\"122\" \/><\/p>\n<\/div>\n<\/div>\n<div>\n<div>\n<h3>The mechanism<\/h3>\n<div>\n<div>\n<h4><strong>Elementary step #1<\/strong><\/h4>\n<p>Part #1: Hydroboration of the alkene. In this first step the addition of the borane to the alkene is initiated and proceeds as a concerted reaction because bond breaking and bond formation occur at the same time. This step involves the vacant 2p orbital of the boron electrophile pairing with the electron pair of the\u00a0\u03c0-bond of the alkene nucleophile.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5077 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21042655\/HydroborationMechanism.png\" alt=\"The B-H bond adds across the double bond of an alkene in one step\" width=\"684\" height=\"101\" \/><\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>In the product, the boron has added to the less substituted carbon of the alkene, which then places the hydrogen on the more substituted carbon. Both, the boron and the hydrogen add simultaneously on the same face of the double bond (syn addition).<\/li>\n<li>Note that a carbocation is not formed. Therefore, no rearrangement takes place.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div>\n<h3>Oxidation of the trialkylborane by hydrogen peroxide<\/h3>\n<\/div>\n<\/div>\n<div>\n<div>\n<p>You will not be required to know this part of the mechanism for this course, but further information is available in the links below.<\/p>\n<h3>Stereochemistry of hydroboration<\/h3>\n<p>The hydroboration reaction is among the few simple addition reactions that proceed cleanly in a <em>syn <\/em>fashion, <em>i.e.<\/em>, the boron and the hydrogen end up on the same side. As noted above, this is a single-step reaction. Since the bonding of the double bond carbons to boron and hydrogen is concerted, it follows that the geometry of this addition must be <em>syn<\/em>. Furthermore, rearrangements are unlikely inasmuch as a discrete carbocation intermediate is never formed.<\/p>\n<p>Since the hydroboration procedure is most commonly used to hydrate alkenes in an anti-Markovnikov fashion, we also need to know the stereoselectivity of the second oxidation reaction, which substitutes a hydroxyl group for the boron atom. Independent study has shown this reaction takes place with retention of configuration so the overall addition of water is also <em>syn<\/em>.<\/p>\n<\/div>\n<div>\n<div class=\"textbox examples\">\n<h3>Further Readings<\/h3>\n<ul>\n<li><a href=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\" target=\"_blank\" rel=\"noopener\">http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation<\/a><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-4694 alignnone\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2018\/08\/01191827\/static_qr_code_without_logo5-150x150.png\" alt=\"\" width=\"150\" height=\"150\" \/><\/p>\n<ul>\n<li><a href=\"http:\/\/www.chemhelper.com\/hydroboration.html\" target=\"_blank\" rel=\"noopener\">http:\/\/www.chemhelper.com\/hydroboration.html<\/a><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-4695 alignnone\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2018\/08\/01192007\/static_qr_code_without_logo3-150x150.png\" alt=\"\" width=\"150\" height=\"150\" \/><\/p>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div>\n<h3>References<\/h3>\n<ol>\n<li>Vollhardt, Peter, and Neil Shore.\u00a0Organic Chemistry: Structure and Function. 5th. New York: W.H. Freeman and Company, 2007.<\/li>\n<li>Foote, S. Christopher, and William H. Brown. Organic Chemistry. 5th. Belmont, CA: Brooks\/Cole Cengage Learning, 2005.<\/li>\n<li>Bruice, Paula Yurkanis. Oragnic Chemistry. 5th. CA. Prentice Hall, 2006.<\/li>\n<li>Bergbreiter E. David , and David P. Rainville. Stereochemistry of hydroboration-oxidation of terminal alkenes.\u00a0J. Org. Chem., 1976, 41 (18), pp 3031\u20133033<\/li>\n<li>Ilich, Predrag-Peter; Rickertsen, Lucas S., and Becker Erienne. Polar Addition to C=C Group: Why Is Anti-Markovnikov Hydroboration-Oxidation of Alkenes Not &#8220;Anti-&#8220;? Journal of Chemical Education., 2006, v83, n11, pg 1681-1685<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div>\n<div>\n<div>\n<div>\n<div>\n<div>\n<div>\n<div class=\"textbox exercises\">\n<h3>Problems<\/h3>\n<div>\n<div>\n<p><strong>What are the products of these following reactions? <\/strong><\/p>\n<p><strong>#1.<\/strong><\/p>\n<p><strong><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5078 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21132457\/HydroborationQ1.png\" alt=\"BH3 adds to 1-methylcyclohexene to give..?\" width=\"248\" height=\"95\" \/><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><strong>#2.<\/strong><\/p>\n<\/div>\n<\/div>\n<div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5079 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21133542\/HydroborationQ2.png\" alt=\"What is hydroboration-oxidation product from (E)-3-methylpent-2-ene\" width=\"345\" height=\"90\" \/><\/p>\n<p><strong>#3.<\/strong><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5080 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21134006\/HydroborationQ3.png\" alt=\"What is hydroboration-oxidation product of 2-methylprop-1-enylcyclohexane?\" width=\"329\" height=\"82\" \/><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Draw the structural formulas for the alcohols that result from hydroboration-oxidation of the alkenes shown.<\/strong><\/p>\n<p><strong>#4.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5081 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21134224\/HydroborationQ4.png\" alt=\"What is the hydroboration-oxidation product from 2-methylbut-2-ene?\" width=\"293\" height=\"86\" \/><\/p>\n<p><strong>#5. (E)-3-methyl-2-pentene\u00a0 <\/strong><\/p>\n<p>If you need a reminder, see the <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/3-2-nomenclature-of-unsaturated-hydrocarbons\/\">section on naming alkenes<\/a>.<\/p>\n<p>&nbsp;<\/p>\n<\/div>\n<\/div>\n<div>\n<div>\n<h3><strong>Answers<\/strong><\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q433977\">Show Solution<\/span><\/p>\n<div id=\"q433977\" class=\"hidden-answer\" style=\"display: none\">\n<p><strong>#1.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5083 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21144408\/HydroborationA1.png\" alt=\"trans-2-methylcyclohexylborane\" width=\"207\" height=\"86\" \/><strong>#2.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5084 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21144703\/HydroborationA2.png\" alt=\"Racemic (2S,3R)-3-methylhexan-2-ol\" width=\"208\" height=\"85\" \/><\/p>\n<p><strong>#3. <\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5085 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21145946\/HydroborationA3.png\" alt=\"Racemic 1-cyclohexyl-2-methyl-propan-1-ol\" width=\"211\" height=\"99\" \/><\/p>\n<p><strong>#4.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5086 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21150217\/HydroborationA4.png\" alt=\"Racemic 3-methylbutan-2-ol\" width=\"184\" height=\"102\" \/><\/p>\n<p><strong>#5.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5087 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/21150338\/HydroborationA5.png\" alt=\"Racemic 3-methylpentan-2-ol\" width=\"207\" height=\"101\" \/><\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<div>\n<div>\n<div>\n<p>Write out the reagents or products (A\u2013D) shown in the following reaction schemes.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5074 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/20030555\/HydroborationQAnswers01a.png\" alt=\"Hydration reactions of 1-methylcyclopentene and 2-methylbut-1-ene\" width=\"337\" height=\"366\" \/><\/p>\n<\/div>\n<div>\n<h3>Solutions<\/h3>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q652262\">Show Solution<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5073 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/20025354\/HydroborationQAnswers01b.png\" alt=\"Answers to questions on hydration of alkenes\" width=\"323\" height=\"328\" \/><\/p>\n<div id=\"q652262\" class=\"hidden-answer\" style=\"display: none\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n<h1>10.8.3. Anti-Markovnikov addition of HBr to alkynes<\/h1>\n<section class=\"mt-content-container\">Most hydrogen halide reactions with alkynes occur in a Markovnikov-manner in which the halide attaches to the most substituted carbon since it is the most positively polarized. A more substituted carbon has more bonds attached to 1) carbons or 2) electron-donating groups such as Fluorine and other halides. However, there are two specific reactions among alkynes where anti-Markovnikov reactions take place: the radical addition of HBr and hydroboration-oxidation reactions. For alkynes, an anti-Markovnikov addition takes place on a terminal alkyne, an alkyne on the end of a chain.<\/p>\n<div id=\"section_1\" class=\"mt-section\">\n<h2 class=\"editable\">HBr Addition With Radical Yields 1-bromoalkene<\/h2>\n<p>The Br of the Hydrogen Bromide (H-Br) attaches to the less substituted 1-carbon of the terminal alkyne shown below in an anti-Markovnikov manner while the Hydrogen proton attaches to the second carbon. As mentioned above, the first carbon is the less substituted carbon since it has fewer bonds attached to carbons and other substituents. The H-Br reagent must also be reacted with heat or some other radicial initiator such as a peroxide in order for this reaction to proceed in this manner. This presence of the radical or heat leads to the anti-Markovnikov addition since it produces the most stable reaction.\u00a0 The mechanism for this reaction will be covered later.<\/p>\n<p><img decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2192\/hbr_(1).JPG?revision=1&amp;size=bestfit&amp;width=550&amp;height=132\" alt=\"hbr (1).JPG\" width=\"550px\" height=\"132px\" \/><\/p>\n<p>The product of a terminal alkyne that is reacted with a peroxide (or light) and H-Br is a 1-bromoalkene.<\/p>\n<p><strong>Regioselectivity<\/strong>: The Bromine can attach in a <strong><em>syn <\/em><\/strong>or <strong><em>anti <\/em><\/strong>manner which means the resulting alkene can be both <strong><em>cis <\/em><\/strong>and<strong> <em>tran<\/em><em>s<\/em><\/strong>. <strong><em>Syn <\/em><\/strong>addition is when both Hydrogens attach to the same face or side of the double bond (i.e. <strong><em>cis<\/em><\/strong>) while the <strong><em>anti<\/em><\/strong> addition is when they attach on opposite sides of the bond (<strong><em>trans<\/em><\/strong>).<\/p>\n<\/div>\n<div id=\"section_2\" class=\"mt-section\">\n<h1>10.8.4. Anti-Markovnikov addition of H<sub>2<\/sub>O to alkynes<\/h1>\n<h2 class=\"editable\">Stereospecific Hydroboration Oxidation of Alkynes<\/h2>\n<p>Boranes such as dicyclohexylborane react with alkynes to give aldehydes, after oxidation of the intermediate borane.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5164 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/15075007\/Cy2BH_Alkyne_HydroborationOxidationOverall.png\" alt=\"Pent-1-yne is converted to pentanal using Cy2BH then alkaline H2O2\" width=\"432\" height=\"90\" \/><\/p>\n<p><strong>Step 1:<\/strong> Hydroboration of terminal alkynes reacts in an anti-Markovnikov fashion in which the boron attacks the less substituted carbon which is the least hindered. It is a stereospecific reaction where <strong><em>syn <\/em><\/strong>addition is observed as the hydroboration occurs on the same side of the alkyne and results in <strong><em>cis <\/em><\/strong>stereochemistry. However, a bulky borane reagent needs to be used to stop at the addition the alkenyl-borane stage. Otherwise, a second hydroboration will occur. Common sterically hindered borane reagents include dicyclohexylborane (written as Cy<sub>2<\/sub>BH) and diisoamyl borane (written as Sia<sub>2<\/sub>BH).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-5158 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/15072229\/Cy2BH_Alkyne_Hydroboration.png\" alt=\"Hydroboration of pent-1-yne to form an alkenylborane\" width=\"432\" height=\"91\" \/><\/p>\n<p><strong>Step 2:<\/strong> Oxidation is the next step that occurs. The resulting alkenylborane is oxidized to an enol due to the reaction with hydrogen peroxide in a basic solution such as aqueous sodium hydroxide. As we saw in <a href=\"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/10-5-simple-addition-to-alkynes\/\">section 10.5<\/a>, an enol will go rapid tautomerization and rearrange into a carbonyl (C=O) compound as the product &#8211; in this case, in basic solution.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-5160 aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3369\/2020\/06\/15073831\/Cy2BH_Alkyne_OxidationStep1.png\" alt=\"Oxidation of an alkenylborane to an enol, then tautomerization to pentanal\" width=\"677\" height=\"94\" \/><\/p>\n<\/div>\n<div id=\"section_2\" class=\"mt-section\">\n<p>For additional information on hydroboration oxidation: See <a href=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\">Hydroboration-oxidation<\/a> in Wikipedia<\/p>\n<\/div>\n<div id=\"section_3\" class=\"mt-section\">\n<h2 class=\"editable\">References<\/h2>\n<ol>\n<li>Brown, Herbert C. <u>Hydroboration With Supplement<\/u>. New York: Addison-Wesley Pub Co, 1980.<\/li>\n<li>Dhillon, Ranjit S. <u>Hydroboration and Organic Synthesis 9-Borabicyclo [3.3.1] nonane (9-BBN)<\/u>. New York: Springer, 2007.<\/li>\n<li>Minkin, V. I. <u>Molecular design of tautomeric compounds<\/u>. Dordrecht: D. Reidel Pub. Co., U.S.A. and Canada, 1988.<\/li>\n<li>Vollhardt, K. Peter C., and Neil E. Schore. <u>Organic Chemistry Structure and Function<\/u>. New York: W. H. Freeman, 2005.<\/li>\n<\/ol>\n<\/div>\n<div id=\"section_4\" class=\"mt-section\">\n<p>&nbsp;<\/p>\n<h2 class=\"editable\">Outside Links<\/h2>\n<ul>\n<li><a class=\"external\" title=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\" href=\"http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation\" target=\"_blank\" rel=\"external nofollow noopener\">http:\/\/en.wikipedia.org\/wiki\/Hydroboration-oxidation<\/a><\/li>\n<li>Markovnikov&#8217;s Rule: <a class=\"external\" title=\"http:\/\/en.wikipedia.org\/wiki\/Markovnikov%27s_rule\" href=\"http:\/\/en.wikipedia.org\/wiki\/Markovnikov%27s_rule\" target=\"_blank\" rel=\"external nofollow noopener\">http:\/\/en.wikipedia.org\/wiki\/Markovnikov%27s_rule<\/a><\/li>\n<li>For more on alkynes: <cite>www.ulm.edu\/~junk\/examkeys\/pp230_7_ch8.ppt<\/cite><\/li>\n<\/ul>\n<\/div>\n<div id=\"section_5\" class=\"mt-section\">\n<p>&nbsp;<\/p>\n<h2 class=\"editable\">Problems<\/h2>\n<p>1. What is the product of this reaction?<\/p>\n<p><img decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2197\/wikiproblem_(3).jpg?revision=1&amp;size=bestfit&amp;width=591&amp;height=243\" alt=\"wikiproblem (3).jpg\" width=\"591px\" height=\"243px\" \/><\/p>\n<p>2. What process causes the conversion of a vinyl alcohol to an aldeyde and what are some of its distinct features?<\/p>\n<p>3. True or False: Only <em>cis <\/em>products are observed in radical H-Br additions to terminal alkynes.<\/p>\n<p>4. Explain why a bulky borane reagent is necessary for hydroboration oxidation reactions.<\/p>\n<p>5. Draw the product.<\/p>\n<\/div>\n<div id=\"section_6\" class=\"mt-section\">\n<h2 class=\"editable\"><img decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2194\/Problem_2.jpg?revision=1&amp;size=bestfit&amp;width=480&amp;height=194\" alt=\"Problem 2.jpg\" width=\"480px\" height=\"194px\" \/><\/h2>\n<\/div>\n<div id=\"section_7\" class=\"mt-section\">\n<p>&nbsp;<\/p>\n<h2 class=\"editable\">Answers<\/h2>\n<p>1. Don&#8217;t be confused by the borane reagent! Just remember, anytime there is a bulky borane reagent reacting with a terminal alkyne, the hydroboration oxidation reaction will occur and be proceeded by tautomerism which will produce an aldeyde as shown below.<\/p>\n<p><img decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2196\/wikianswer.jpg?revision=1&amp;size=bestfit&amp;width=472&amp;height=190\" alt=\"wikianswer.jpg\" width=\"472px\" height=\"190px\" \/><\/p>\n<p>2. The interconversion of an enol or vinyl alcohol to an aldehyde is called tautomerism and it is very distinct since it is a spontaneous reaction that proceeds very quickly.<\/p>\n<p>3. False. Both <em>cis <\/em>and <em>trans<\/em> products are produced as both <em>syn <\/em>and <em>anti<\/em> additions are observed.<\/p>\n<p>4. If a small borane reagent is utilized, both pi bonds will be used and a second hydroboration will occur. This will break the double bond of the alkene and the aldehyde product will not be formed.<\/p>\n<p>5.<\/p>\n<p><img decoding=\"async\" class=\"internal default\" src=\"https:\/\/chem.libretexts.org\/@api\/deki\/files\/2193\/Problem_2_answer.jpg?revision=1&amp;size=bestfit&amp;width=169&amp;height=163\" alt=\"Problem 2 answer.jpg\" width=\"169px\" height=\"163px\" \/><\/p>\n<\/div>\n<div id=\"section_8\" class=\"mt-section\">\n<p>&nbsp;<\/p>\n<h2 class=\"editable\">Contributors<\/h2>\n<ul>\n<li>Ali Alvandi<\/li>\n<\/ul>\n<\/div>\n<\/section>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-5034\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Original<\/div><ul class=\"citation-list\"><li>HBr addition to alkenes, also complete rewrite and many new graphics for hydroboration-oxidation. <strong>Authored by<\/strong>: Martin A. Walker. <strong>Provided by<\/strong>: SUNY Potsdam. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\">CC BY-SA: Attribution-ShareAlike<\/a><\/em><\/li><\/ul><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Some hydroboration-oxidation content. <strong>Authored by<\/strong>: Ali Alvandi . <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/chem.libretexts.org\/Bookshelves\/Organic_Chemistry\/Map%3A_Organic_Chemistry_(Smith)\/Chapter_11%3A_Alkynes\/11.10%3A_Hydroboration%E2%80%93Oxidation\">https:\/\/chem.libretexts.org\/Bookshelves\/Organic_Chemistry\/Map%3A_Organic_Chemistry_(Smith)\/Chapter_11%3A_Alkynes\/11.10%3A_Hydroboration%E2%80%93Oxidation<\/a>. <strong>Project<\/strong>: Libretexts. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><li><strong>Authored by<\/strong>: Ali Alvandi. <strong>Provided by<\/strong>: Libretexts. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/chem.libretexts.org\/Bookshelves\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Alkynes\/Reactivity_of_Alkynes\/Anti-Markovnikov_Additions_to_Triple_Bonds\">https:\/\/chem.libretexts.org\/Bookshelves\/Organic_Chemistry\/Supplemental_Modules_(Organic_Chemistry)\/Alkynes\/Reactivity_of_Alkynes\/Anti-Markovnikov_Additions_to_Triple_Bonds<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><li><strong>Authored by<\/strong>: Gilbert Torres, Ali Alvandi. <strong>Provided by<\/strong>: UC-Davis. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/chem.libretexts.org\/Courses\/University_of_Illinois%2C_Springfield\/UIS%3A_CHE_267_-_Organic_Chemistry_I_(Morsch)\/Chapters\/Chapter_11%3A_Alkynes\/11.10%3A_Hydroboration%E2%80%93Oxidation_of_Alkynes\">https:\/\/chem.libretexts.org\/Courses\/University_of_Illinois%2C_Springfield\/UIS%3A_CHE_267_-_Organic_Chemistry_I_(Morsch)\/Chapters\/Chapter_11%3A_Alkynes\/11.10%3A_Hydroboration%E2%80%93Oxidation_of_Alkynes<\/a>. <strong>Project<\/strong>: Libretexts. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":96103,"menu_order":8,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Some hydroboration-oxidation content\",\"author\":\"Ali Alvandi \",\"organization\":\"\",\"url\":\"https:\/\/chem.libretexts.org\/Bookshelves\/Organic_Chemistry\/Map%3A_Organic_Chemistry_(Smith)\/Chapter_11%3A_Alkynes\/11.10%3A_Hydroboration%E2%80%93Oxidation\",\"project\":\"Libretexts\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"},{\"type\":\"original\",\"description\":\"HBr addition to alkenes, also complete rewrite and many new graphics for hydroboration-oxidation\",\"author\":\"Martin A. 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