{"id":6401,"date":"2012-03-12T07:39:25","date_gmt":"2012-03-12T07:39:25","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=6401"},"modified":"2012-03-12T13:49:49","modified_gmt":"2012-03-12T13:49:49","slug":"spotting-the-unexpected-the-hydration-of-formaldehyde","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6401","title":{"rendered":"Spotting the unexpected. The hydration of formaldehyde."},"content":{"rendered":"
\n

In my\u00a0previous post<\/a>\u00a0I speculated why bis<\/em>(trifluoromethyl) ketone tends to fully form a hydrate when dissolved in water, but acetone does not. Here I turn to asking why\u00a0formaldehyde is also 80% converted to methanediol<\/a>\u00a0in water? Could it be that again, the diol is somehow preferentially stabilised compared to the carbonyl precursor and if so, why?<\/p>\n

\"\"

Methanediol.<\/p><\/div>\n

The lowest energy geometry is shown above. Conspicuously, it does not form an intramolecular O-H…O hydrogen bond, but adopts a C2<\/sub>-symmetric form.\u00a0NBO analysis for this geometry reveals two interactions larger than the rest. The first, shown below, involves overlap of an oxygen lone pair (Lp) donor orbital with a C-H acceptor (purple+blue, orange-red), and this is worth E(2) 6.1 kcal\/mol (there are two of these). Unfortunately, the analogous NBO interaction in acetone itself originating from a C-Me bond as acceptor is 6.3 kcal\/mol and so this interaction does not differentiate between the two.<\/p>\n

\"\"

NBO interaction between O Lp and a C-H acceptor. Click for 3D<\/p><\/div>
\nThe larger NBO interaction of E(2) = 16.9 kcal\/mol arises from the same donor orbital interacting with the C-O acceptor (the presence of the more electronegative oxygen accounts for it being the better acceptor). In acetone however, this too has the high value of 16.8 kcal\/mol.<\/p>\n

\"\"

NBO interaction between Oxygen Lp and C-O acceptor. Click for 3D.<\/p><\/div>Another possible interaction might be from a H-C donor to a C-O acceptor. But as you can see below, the positive overlap (red+orange) is matched by the negative overlap (orange+blue) and this interaction turns out to be insignificant.<\/p>\n

\"\"

interaction between a C-H donor and a C-O acceptor. Click for 3D<\/p><\/div>We have to seek elsewhere for differentiation between formaldehyde and acetone. To do this, I have added four explicit water molecules as solvent, and looked at the free energies of diol formation from the carbonyl (wB97XD\/6-311G(d,p)\/scrf=water<\/a>).<\/p>\n\n\n\n
\"\"

Methanediol with four water molecules. Click for 3D.<\/p><\/div><\/td>\n

\n

\"\"<\/a>

Propanediol with four water molecules.<\/p><\/div><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The water molecules combine with the methanediol to form an elegant lattice of hydrogen bonds, involving two rings of three oxygens and one ring of four oxygens. This compact motif is less stable for propanediol, which instead prefers a structure forming fewer hydrogen bonds, largely because of the presence of the hydrophobic methyl groups. The result is that the free energy of hydration of formaldehyde to the diol, assisted by hydrogen bonds formed to four water molecules, is exothermic at -1.2 kcal\/mol, whereas that for acetone is endothermic at \u00a0+7.5 kcal\/mol.<\/p>\n

As with most things water, a proper stochastic exploration of all the possible configurations of the hydrogen bonds is necessary for a definitive explanation. But it does seem that a probable theory for why formaldehyde readily forms a diol whereas acetone does not lies not so much in stereoelectronic donor-acceptor interactions but in the hydrogen bonds set up in the solvated diol.<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

In my\u00a0previous post\u00a0I speculated why bis(trifluoromethyl) ketone tends to fully form a hydrate when dissolved in water, but acetone does not. Here I turn to asking why\u00a0formaldehyde is also 80% converted to methanediol\u00a0in water? Could it be that again, the diol is somehow preferentially stabilised compared to the carbonyl precursor and if so, why? The […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_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},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[40,815,814,816,810,373],"ppma_author":[2661],"class_list":["post-6401","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-free-energy","tag-lowest-energy-geometry","tag-o-lp","tag-oxygen-lp","tag-solvation","tag-tutorial-material"],"yoast_head":"\nSpotting the unexpected. The hydration of formaldehyde. - 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=6401\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Spotting the unexpected. The hydration of formaldehyde. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"In my\u00a0previous post\u00a0I speculated why bis(trifluoromethyl) ketone tends to fully form a hydrate when dissolved in water, but acetone does not. Here I turn to asking why\u00a0formaldehyde is also 80% converted to methanediol\u00a0in water? Could it be that again, the diol is somehow preferentially stabilised compared to the carbonyl precursor and if so, why? The […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6401\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2012-03-12T07:39:25+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2012-03-12T13:49:49+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/03\/formaldehyde-diol.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":"Spotting the unexpected. The hydration of formaldehyde. - 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=6401","og_locale":"en_GB","og_type":"article","og_title":"Spotting the unexpected. The hydration of formaldehyde. - Henry Rzepa's Blog","og_description":"In my\u00a0previous post\u00a0I speculated why bis(trifluoromethyl) ketone tends to fully form a hydrate when dissolved in water, but acetone does not. Here I turn to asking why\u00a0formaldehyde is also 80% converted to methanediol\u00a0in water? Could it be that again, the diol is somehow preferentially stabilised compared to the carbonyl precursor and if so, why? The […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6401","og_site_name":"Henry Rzepa's Blog","article_published_time":"2012-03-12T07:39:25+00:00","article_modified_time":"2012-03-12T13:49:49+00:00","og_image":[{"url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/03\/formaldehyde-diol.jpg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"3 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6401#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6401"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Spotting the unexpected. 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The initial intent was to estimate the \"flattening\" energy. There are six electronic possibilities for this molecule on a metal surface. Respectively positively, or\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":[]},{"id":6477,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6477","url_meta":{"origin":6401,"position":1},"title":"Stereoselectivities of Proline-Catalyzed Asymmetric Intermolecular Aldol Reactions.","author":"Henry Rzepa","date":"April 22, 2012","format":false,"excerpt":"Astronomers who discover an asteroid get to name it, mathematicians have theorems named after them. Synthetic chemists get to name molecules (Hector's base and Meldrum's acid spring to mind) and reactions between them. What do computational chemists get to name? Transition states! One of the most famous of recent years\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":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/04\/Houk.svg","width":350,"height":200},"classes":[]},{"id":7964,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7964","url_meta":{"origin":6401,"position":2},"title":"Text-books and the bromination of ethene.","author":"Henry Rzepa","date":"October 14, 2012","format":false,"excerpt":"There is often a disconnect between how a text-book (schematically) represents a reaction and a more quantitive \"reality\" revealed by quantum mechanics. Is the bromination of ethene to give 1,2-dibromoethane one such example? Text-books will show how ethene interacts with bromine to form a cyclic bromonium cation, which with the\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\/Br2b2.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":8570,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8570","url_meta":{"origin":6401,"position":3},"title":"The mechanism of the Birch reduction. Sequel to benzene reduction.","author":"Henry Rzepa","date":"December 5, 2012","format":false,"excerpt":"I noted briefly in discussing why Birch reduction of benzene gives 1,4-cyclohexadiene (diagram below) that the geometry of the end-stage pentadienyl anion was distorted in the presence of the sodium cation to favour this product. This distortion actually has some pedagogic value, and so I elaborate this here. The starting\u2026","rel":"","context":"In \"antiaromaticity\"","block_context":{"text":"antiaromaticity","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=antiaromaticity"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/benzene-22.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":25043,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=25043","url_meta":{"origin":6401,"position":4},"title":"Geometries of proton transfers: modelled using total energy or free energy?","author":"Henry Rzepa","date":"April 18, 2022","format":false,"excerpt":"Proton transfers are amongst the most common of all chemical reactions. They are often thought of as \"trivial\" and even may not feature in many mechanistic schemes, other than perhaps the notation \"PT\".\u00a0The types with the lowest energy barriers for transfer often involve heteroatoms such as N and O, and\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2022\/04\/plot-1024x734.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":20679,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20679","url_meta":{"origin":6401,"position":5},"title":"Imaging vibrational normal modes of a single molecule.","author":"Henry Rzepa","date":"April 18, 2019","format":false,"excerpt":"The topic of this post originates from a recent article which is attracting much attention. The technique uses confined light to both increase the spatial resolution by around three orders of magnitude and also to amplify the signal from individual molecules to the point it can be recorded. To me,\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.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/04\/Figure3a-1024x529.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"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\/6401","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=6401"}],"version-history":[{"count":29,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6401\/revisions"}],"predecessor-version":[{"id":6437,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6401\/revisions\/6437"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6401"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6401"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6401"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=6401"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}