29Si NMR Investigation of Si-alkylsubstituted 1,3,5-Trisilacyclohexanes

✍ Scribed by Ingvar Arnason

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: German
• Weight: 88 KB
• Volume: 625
• Category: Article
• ISSN: 0372-7874
• DOI: 10.1002/(sici)1521-3749(199901)625:1<97::aid-zaac97>3.0.co;2-h

✦ Synopsis

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Si NMR spectra of 29 Si-alkylsubstituted derivatives of 1,3,5-trisilacyclohexanes have been recorded and analyzed. A systematic preparation of alkyl derivatives with mixed substituents made it possible to evaluate substituentinduced chemical shift (SCS) values for the ring silicon atoms in α and c position. It is found that the equatorial αeffect increases in the order Me < Et < i-Pr < t-Bu. For the alkyl groups Me, Et, and i-Pr the axial α-effect is similar in magnitude to the α e -effect. Axial SCS values for the t-Bu group are not accessible because chair conformations with an axial t-Bu group are energetically unfavourable and escape into a twisted boat form. The observed c-effects exhibit the c gauche -effect for axial substituents as known from compounds with a pure carbon framework.