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Gas‐phase intramolecular anion rearrangements of some trimethylsilyl‐containing systems revisited. A theoretical approach
Author(s) -
Wang Tianfang,
Bowie John H.
Publication year - 2009
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4363
Subject(s) - chemistry , organosilicon , intramolecular force , trimethylsilyl , ion , silicon , ab initio , bond cleavage , transition state , computational chemistry , crystallography , medicinal chemistry , catalysis , stereochemistry , polymer chemistry , organic chemistry
Abstract Ab initio calculations at the CCSD(T)/6‐311++G(2d,p)//B3LYP/6‐311++G(d,p) level of theory have been carried out for three prototypical rearrangement processes of organosilicon anion systems. The first two are reactions of enolate ions which involve oxygen–silicon bond formation via three‐ and four‐membered states, respectively. The overall reactions are:$${\rm CH}_2 {\rm = C}({\rm O}^ - ){\rm Si}({\rm CH}_3 )_3 \to ({\rm CH}_3 )_3 {\rm SiO}^ - + {\rm CH}_2 {\rm C},\,\,\,{\rm and}$$$$({\rm CH}_3 )_3 {\rm SiCH = CHO}^ - \to ({\rm CH}_3 )_3 {\rm SiO}^ - + {\rm C}_{\rm 2} {\rm H}_2 $$The ΔG (reaction) values for the two processes are +175 and +51 kJ mol −1 , with maximum barriers (to the highest transition state) of +55 and +159 kJ mol −1 , respectively. The third studied process is the following: (CH 3 O)C(CH 2 )Si(CH 3 ) 2 CH 2 − → (CH 3 ) 2 (C 2 H 5 )Si − + CH 2 CO, a process involving an S N i reaction between ‐CH 2 −and CH 3 O‐ followed by silicon–carbon bond cleavage. The reaction is favourable [ΔG(reaction) = −39 kJ mol −1 ] with the barrier for the S N i process being 175 kJ mol −1 . The previous experimental and the current theoretical data are complementary and in agreement. Copyright © 2009 John Wiley & Sons, Ltd.