{"id":4837,"date":"2011-09-04T18:33:43","date_gmt":"2011-09-04T18:33:43","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=4837"},"modified":"2011-09-18T11:20:47","modified_gmt":"2011-09-18T11:20:47","slug":"anatomy-of-a-simple-reaction-the-hydration-of-an-alkene","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4837","title":{"rendered":"Anatomy of a simple reaction: the hydration of an alkene."},"content":{"rendered":"
\n

The hydration of an alkene by an acid is one of those fundamental reactions, taught early on in most chemistry courses. What can quantum mechanics teach us about the mechanism of the reaction?<\/p>\n

\"\"<\/a>

The hydration of ethene by a hydronium cation.<\/p><\/div>\n

The diagram below shows us the IRC, or intrinsic reaction coordinate for the process (for definitions, see here<\/a>), the reaction proceeding from left to right as shown in the scheme above, with a (free energy) barrier of 14.4 kcal\/mol and exothermic by a similar amount (wB97XD\/6-311G(d,p)<\/a> with a continuum solvation correction for water).<\/p>\n

\"\"<\/p>\n

One first notices that it is not the smooth bell-shaped profile that is normally drawn in text books. It has bumps\/detail. What do these mean? Before dissecting, lets look at another plot, this time the RMS (root mean square) gradients of the 3N-6 geometric variables along the reaction coordinates. These reveal two regions where the RMS gradient is almost zero (other than reactant and product).<\/p>\n

\"\"<\/p>\n\n\n\n\n
1<\/th>\n2<\/th>\n3<\/th>\n<\/tr>\n
\"\"

Hydrogen-bonded reactant<\/p><\/div><\/td>\n

\"\"

Forming bridged protonated ethene<\/p><\/div><\/td>\n

\"\"

The transition state Click for 3D.<\/p><\/div><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n
4<\/th>\n5<\/th>\n<\/tr>\n
\"\"

Second phase, C-O bond formation<\/p><\/div><\/td>\n

\"\"

Rotating from eclipsed to staggered<\/p><\/div><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Five distinct stages can be seen.<\/p>\n

    \n
  1. The hydronium ion approaches the ethene, and forms quite a strong \u03c0-facial hydrogen bond.<\/li>\n
  2. Water now starts separating from the hydrogen bonded complex, thus relocating the H-bond from the alkene to the water.<\/li>\n
  3. The formal transition state (the only one) is reached, with the proton moving from the symmetric bridged ethyl cation to one end, and the water is starting to move to the other end. Not perhaps the most obvious of transition states!<\/li>\n
  4. The formation of the C-O bond is now completing, and the C-C bond is now almost purely converted from double to single.<\/li>\n
  5. Only at this stage does the eclipsed conformation of the newly formed ethanol start to rotate into a staggered and final conformation.<\/li>\n
  6. Overall, the reaction is concerted (if not synchronous), and its reverse would be classified as an E2 elimination.<\/li>\n<\/ol>\n

    You can see quite a lot of simple basic principles in chemistry are illustrated along this reaction coordinate. We have space for one more: what happens if you make the alkene very much more reactive? How about cyclobutadiene, which in avoiding anti-aromaticity, has become highly reactive.<\/p>\n

    \"\"<\/a>

    Hydration of cyclobutadiene.<\/p><\/div>\n

    The IRC for this variation is shown below. Notice now the much smaller barrier to reaction (~0.4 kcal\/mol in \u0394G), and the much greater exothermicity overall.<\/p>\n

    \"\"<\/p>\n

    \"\"<\/p>\n

    The transition state is also different. It corresponds to proton transfer from the hydronium cation to one carbon of the cyclobutadiene, to form a stabilised allyl cation. In terms of the reverse elimination, this now corresponds to an E1 type, involving an intermediate species, and the reaction is no longer concerted.<\/p>\n

    \"\"

    The transition state for protonation of cyclobutadiene<\/p><\/div>I will stop here, reminding that these two simple reactions have taught us a lot about basic organic chemistry.<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    The hydration of an alkene by an acid is one of those fundamental reactions, taught early on in most chemistry courses. What can quantum mechanics teach us about the mechanism of the reaction? The diagram below shows us the IRC, or intrinsic reaction coordinate for the process (for definitions, see here), the reaction proceeding from […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[],"tags":[663,40,664,666,665,373],"ppma_author":[2661],"class_list":["post-4837","post","type-post","status-publish","format-standard","hentry","tag-alkene","tag-free-energy","tag-hydration","tag-intrinsic-reaction-coordinate","tag-irc","tag-tutorial-material"],"yoast_head":"\nAnatomy of a simple reaction: the hydration of an alkene. - Henry Rzepa's Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4837\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Anatomy of a simple reaction: the hydration of an alkene. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"The hydration of an alkene by an acid is one of those fundamental reactions, taught early on in most chemistry courses. What can quantum mechanics teach us about the mechanism of the reaction? The diagram below shows us the IRC, or intrinsic reaction coordinate for the process (for definitions, see here), the reaction proceeding from […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4837\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2011-09-04T18:33:43+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2011-09-18T11:20:47+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/09\/hydration.jpg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Anatomy of a simple reaction: the hydration of an alkene. - Henry Rzepa's Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4837","og_locale":"en_GB","og_type":"article","og_title":"Anatomy of a simple reaction: the hydration of an alkene. - Henry Rzepa's Blog","og_description":"The hydration of an alkene by an acid is one of those fundamental reactions, taught early on in most chemistry courses. 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Alkyne metathesis is closely related to the same reaction for alkenes, and one catalyst that is specific to alkynes was introduced by Schrock (who with Grubbs won the Nobel prize for these discoveries) and\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/10\/schrock.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":7420,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7420","url_meta":{"origin":4837,"position":1},"title":"Curly arrow pushing: another reality check.","author":"Henry Rzepa","date":"August 5, 2012","format":false,"excerpt":"Two years ago, I discussed how curly arrow pushing is taught, presenting four different ways of showing the arrows.\u00a0One of the comments posted to that blog suggested that all of the schemes shown below were deficient in one aspect. The issues were the stereo and regiochemistry. In particular, the diagram\u2026","rel":"","context":"In "Curly arrows"","block_context":{"text":"Curly arrows","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2327"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/10\/arrow_pushing.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":5087,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=5087","url_meta":{"origin":4837,"position":2},"title":"cis-Butene: a reaction coordinate dissected and methyl flags.","author":"Henry Rzepa","date":"October 12, 2011","format":false,"excerpt":"In two previous posts, I have looked at why cis-butene adopts conformation (a) rather than (b). I suggested it boiled down to electronic interactions between the methyl groups and the central alkene resulting in the formation of a H...H \"topological\" bond, rather than attraction between the H...H region to form\u2026","rel":"","context":"In "General"","block_context":{"text":"General","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/10\/cis-butene2.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":7444,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7444","url_meta":{"origin":4837,"position":3},"title":"The stereochemical origins of the Wittig reaction.","author":"Henry Rzepa","date":"August 7, 2012","format":false,"excerpt":"This is another of those textbook reactions, involving reaction of a carbonyl compound with a phosphonium ylid to form an alkene and a phosphine oxide. The reaction continues to be frequently used, in part because it can be highly stereospecific.\u00a0 Thus the standard version tends to give Z-alkenes with good\u2026","rel":"","context":"In \"Reaction Mechanism\"","block_context":{"text":"Reaction Mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=reaction-mechanism"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/08\/wittig.svg","width":350,"height":200,"srcset":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/08\/wittig.svg 1x, http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/08\/wittig.svg 1.5x, http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/08\/wittig.svg 2x"},"classes":[]},{"id":8375,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8375","url_meta":{"origin":4837,"position":4},"title":"The regiospecificity of di-imide reduction of an alkene.","author":"Henry Rzepa","date":"November 25, 2012","format":false,"excerpt":"Not a few posts on this blog dissect the mechanisms of well known text-book reactions. But one reaction type where there are few examples on these pages are reductions. These come in three types; using electrons, using a hydride anion and using di-hydrogen. Here I first take a closer look\u2026","rel":"","context":"In \"free energy discrimination\"","block_context":{"text":"free energy discrimination","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=free-energy-discrimination"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/11\/diimide.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":26812,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=26812","url_meta":{"origin":4837,"position":5},"title":"Mechanistic templates computed for the Grubbs alkene-metathesis reaction.","author":"Henry Rzepa","date":"February 19, 2024","format":false,"excerpt":"Following on from my template exploration of the Wilkinson hydrogenation catalyst, I now repeat this for the Grubbs variant of the Alkene metathesis reaction. As with the Wilkinson, here I focus on the stereochemistry of the mechanism as first suggested by Chauvin, an aspect lacking in eg the Wikipedia entry.\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4837","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4837"}],"version-history":[{"count":0,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4837\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4837"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4837"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4837"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=4837"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}