{"id":1278,"date":"2009-12-06T11:56:14","date_gmt":"2009-12-06T10:56:14","guid":{"rendered":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1278"},"modified":"2009-12-06T11:56:14","modified_gmt":"2009-12-06T10:56:14","slug":"the-nature-of-the-c%e2%89%a1s-triple-bond-part-3","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2009\/12\/06\/the-nature-of-the-c%e2%89%a1s-triple-bond-part-3\/","title":{"rendered":"The nature of the C\u2261S triple bond: part 3."},"content":{"rendered":"

In the previous two posts<\/a>, a strategy for tuning the nature of the CS bond in the molecule HO-S\u2261C-H was developed, based largely on the lone pair of electrons identified on the carbon atom. By replacing the HO group by one with greater \u03c3-electron withdrawing propensity, the stereo-electronic effect between the O-S bond and the carbon lone pair was enhanced, and in the process, the SC bond was strengthened. It is time to do a control experiment<\/span> in the other direction. Now, the HO-S group is replaced by a H2<\/span>B-S group. The B-S bond, boron being very much less electronegative than oxygen, should be a very poor \u03c3-acceptor. In addition, whereas oxygen was a \u03c0-electron donor (acting to strengthen the S=C region), boron is a \u03c0-acceptor, and will also act in the opposite direction. So now, this group should serve to weaken the S-C bond.<\/p>\n<\/p>\n

\n
\n
\"The<\/dt>\n
The H2BSCH molecule. Click for 3D.<\/dd>\n<\/dl>\n<\/div>\n

At the B3LYP\/cc-pVTZ level (DOI: 10042\/to-3189<\/a>), the S-C bond now emerges as 1.834\u00c5 compared to 1.544\u00c5 for the HO-substituted version and the S-C stretch is reduced to 803 cm-1<\/span>. The NBO interaction term between LP(1)C2 and BD*(1) S1-B3 is indeed quite small (6.9 kcal\/mol). The basin integration for point 10<\/span> increases to 2.22e, whilst point 9<\/span> decreases to 1.90e, and 8<\/span> is again up at 2.11. The SC bond is now merely a single bond!<\/p>\n<\/p>\n

So what have we proved? Well, we find that our hypothesis works in both directions, to either strengthen or weaken the CS region. Indeed, variation of the S-substituent (HO, OTf, BH2) has quite a dramatic effect on the nature of the CS bond, evolving it all the way from a single bond at one extreme to one with significantly triple character at the other.<\/p>\n","protected":false},"excerpt":{"rendered":"

In the previous two posts, a strategy for tuning the nature of the CS bond in the molecule HO-S\u2261C-H was developed, based largely on the lone pair of electrons identified on the carbon atom. By replacing the HO group by one with greater \u03c3-electron withdrawing propensity, the stereo-electronic effect between the O-S bond and the […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10,11],"tags":[1230,1290],"class_list":["post-1278","post","type-post","status-publish","format-standard","hentry","category-hypervalency","category-interesting-chemistry","tag-hypervalency","tag-interesting-chemistry"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/1278","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=1278"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/1278\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=1278"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=1278"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=1278"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}