1990 Fiscal Year Final Research Report Summary
Mechanistic Analysis for Sigma-Participation Based on Silicon Effects
| Project/Area Number |
01470025
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
有機化学一般
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| Research Institution | Kyshu University |
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Principal Investigator |
SHIMIZU Nobujirou Kyushu Univ. Fac. Sci., Associate Prof., 理学部, 助教授 (70001849)
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| Project Period (FY) |
1989 – 1990
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| Keywords | sigma-Participation / Carbocation Stability / Hyperconjugation / Solvolysis / beta-Silicon Effect |
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| Research Abstract |
Kinetics and products have been investigated in detail for the solvolysis of alpha- or beta-silyl-substituted benzylic derivatives, i. e., alpha- (pentamethyldisilanyl) benzyl halides (1), 2, 2, 3, 3-tetramethy1-2, 3-disila-1-indanyl chloride (2), 2, 2-dimethy1-2-sila-1-indanyl halides (3), 1-pheny1-2-(trimethylsily) ethyl trifluroacetate (4), 2-phenyl-1- (pentamethyldisilanyl) cyclopropyl bromide (5), and 2-phenyl-2- (trimethylsilyl) ethyl trifluroacetate (6), and other related derivatives. The following observations are instructive. (1) alpha-Silicon destabilizes the benzylic cation by 3-4 kacal/mol relative to carbon ; (2) alpha- (Disilanyl) benzyl cation and alpha- (trimethylsilylmethyl) -benzyl cation are respectively 6.2-6.8 and 7.2 kcal/mol more stable than the corresponding alpha- (trialkylsilyl) benzyl cation and alpha-alkylbenzyl cation ; (3) 1 solvolyzes via kc mechanism despite a marked rate acceleration by the beta-silyl group and a rearrangement of this group seemingly characteristic of sigma-participation ; (4) The alpha-disilanyl compound 2 in which the Si-Si bond is orthogonal to the leaving group exhibits no beta-silicon effect indicative of hyperconjugative origin for the betasillic on effect ; (5) In sigma-participated (4) or aryl-paticipated solvolysis (5), the presence of the beta-silicon allows the kc solvolysis to occur exclusively or competitively.
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Research Products
(8 results)
