{"id":19569,"date":"2018-04-18T07:58:23","date_gmt":"2018-04-18T06:58:23","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=19569"},"modified":"2018-04-18T07:58:23","modified_gmt":"2018-04-18T06:58:23","slug":"aromaticity-induced-basicity","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=19569","title":{"rendered":"Aromaticity-induced basicity."},"content":{"rendered":"
\n

The molecules below were discussed in the previous post as examples of highly polar but formally neutral molecules, a property induced by aromatisation of up to three rings. Since e.g.<\/em> compound 3<\/strong> is known only in its protonated phenolic form, here I take a look at the basicity of the oxygen in these systems to see if deprotonation of the ionic phenol form to the neutral polar form is viable.<\/p>\n

\"\"<\/a><\/p>\n

The equilibrium being considered is shown below for compound 2<\/strong>:\"\"<\/a><\/p>\n

The energetics of this equilibrium shown below, computed at the \u03c9B97XD\/Def2-TZVPPD\/SCRF=water level and for which the FAIR data DOI is\u00a010.14469\/hpc\/4073<\/a><\/p>\n

For 1: X=Cl<\/strong>, the energy is shown below as a function of the O….H distance. Proton abstraction from HCl is exothermic by ~25 kcal\/mol.<\/p>\n

\"\"<\/a> For 2: X=Cl<\/strong>, the exothermicity increases by only ~5 kcal\/mol , despite the apparent aromatisation of a further ring. It is also worth noting that this is greater basicity than that of e.g.<\/strong> water, where around 4-5 water molecules acting in concert are required<\/a> to deprotonate HCl.\"\"<\/a>For 1: X=OH<\/strong>, the proton abstraction from water is mildly endothermic by about 13 kcal\/mol; indeed there is no energy minimum for carbonyl protonation and instead a relatively strong hydrogen bond to the water is formed instead.
\n \"\"<\/a><\/p>\n

For 2: X=OH<\/strong> the endothermicity is reduced to ~9 kcal\/mol.\"\"<\/a><\/p>\n

For 1: X=CH3<\/sub><\/strong>, deprotonation of methane is now strongly endothermic by ~40 kcal\/mol.<\/p>\n

\"\"<\/p>\n

So the molecules 1 – 2<\/strong> above are clearly not superbases,\u00a0which perhaps augers well for being able to deprotonate the ionic phenols into these neutral but highly polar molecules.<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

The molecules below were discussed in the previous post as examples of highly polar but formally neutral molecules, a property induced by aromatisation of up to three rings. Since e.g. compound 3 is known only in its protonated phenolic form, here I take a look at the basicity of the oxygen in these systems to […]<\/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,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[6],"tags":[2426,2128,1416,147,2438,1977,1987,2453,1504],"class_list":["post-19569","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-antiseptics","tag-aromatization","tag-chemistry","tag-energy","tag-energy-minimum","tag-hydrogen","tag-molecule","tag-neurotoxins","tag-science"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-55D","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/19569","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=19569"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/19569\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=19569"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=19569"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=19569"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}