{"id":16646,"date":"2016-08-04T14:25:32","date_gmt":"2016-08-04T13:25:32","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=16646"},"modified":"2016-08-04T14:25:32","modified_gmt":"2016-08-04T13:25:32","slug":"stereoelectronic-effects-galore-bistrifluoromethyltrioxide","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2016\/08\/04\/stereoelectronic-effects-galore-bistrifluoromethyltrioxide\/","title":{"rendered":"Stereoelectronic effects galore: bis(trifluoromethyl)trioxide."},"content":{"rendered":"

Here is a little molecule that can be said to be pretty electron rich. There are lots of lone pairs present, and not a few electron-deficient \u03c3-bonds. I thought it might be fun to look at the stereoelectronic interactions set up in this little system.<\/p>\n

\"Trioxide\"<\/p>\n

Known as ZEYDOW in the crystal structure database[cite]10.1002\/anie.199522441[\/cite] (this species has a melting point of -138C, and its no trivial matter to measure x-ray diffraction of such a crystal!);\u00a0a\u00a0\u03c9B97XD\/Def2-TZVPP calculation is used to quantify the electron density [cite]10.14469\/ch\/195291[\/cite] and this is then subjected to localisation using the ELF function. The little purple spheres represent so-called monosynaptic electron basins, or lone pairs as we might rather loosely call them (pair is not always an accurate term).\u00a0<\/p>\n

\"zeydow\"<\/p>\n

How these “lone pairs” act as electron donors into empty \u03c3*<\/sup> acceptors can be quantified using NBO theory. The following table shows as many as 24<\/strong> strong interactions (> 10 kcal\/mol). \u00a0This now augments my previous post on “Anomeric effects at carbon involving lone pairs originating from one or two nitrogens<\/a>” and represents an example of “Anomeric effects at oxygen<\/strong> involving lone pairs originating from oxygen”.<\/p>\n

The final two entries originate from lone pairs on the central oxygen, donating approximately antiperiplanar (~160\u00b0) into the O-CF3<\/sub>\u00a0antibonds, but with only a low value of the E(2) interaction energy. These two lone pairs are curiously inert.<\/p>\n\n\n\n\n\n\n\n\n
Lone pair donor<\/th>\n\u03c3-acceptor<\/th>\nNBO E(2) energy<\/th>\n<\/tr>\n
On F: 16,17,18,19,25,35,36,39,40,41,43,45<\/td>\nC-F<\/td>\n18-20<\/td>\n<\/tr>\n
On F: 26,34,37,39,42,44<\/td>\nC-O<\/td>\n11-18<\/td>\n<\/tr>\n
On O: 27,28,24,33<\/td>\nC-F<\/td>\n13-16<\/td>\n<\/tr>\n
On O: 27,33<\/td>\nC-O<\/td>\n13<\/td>\n<\/tr>\n
On O: 30,31<\/td>\nC-O<\/td>\n3.5<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Apart from this curious molecule, there are few other examples of the R-O-O-O-R functional group,[cite]10.5517\/CC7JFCJ[\/cite] but this one did catch my eye,[cite]10.1016\/0022-328X(94)05072-J[\/cite] largely because it was retrieved from a search specification of R-O-O-O-R. The central oxygen apparently supports six O-O bonds, as well as three hydrogens. It is nothing of the sort of course. Reading the text reveals it is really three O…H-O bonds, disordered into two equally probable positions. There are no O-O bonds present at all, which reminds us we must always subject structures derived from x-ray crystallography to a chemical reality check.
\n \"yocsis\"<\/p>\n","protected":false},"excerpt":{"rendered":"

Here is a little molecule that can be said to be pretty electron rich. There are lots of lone pairs present, and not a few electron-deficient \u03c3-bonds. I thought it might be fun to look at the stereoelectronic interactions set up in this little system. Known as ZEYDOW in the crystal structure database[cite]10.1002\/anie.199522441[\/cite] (this species […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,11],"tags":[425,2230,2322,2627],"class_list":["post-16646","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","category-interesting-chemistry","tag-chemical-bonding","tag-sigma-bond","tag-stereoelectronic-effect","tag-x-ray"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/16646","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/comments?post=16646"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/16646\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=16646"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=16646"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=16646"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}