Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : IV. Proton and carbon-13 NMR data for ortho-, 2,6-, and poly-substituted aryltrimethyltins

Abstract

Proton and carbon-13 NMR data recorded in the Fourier transform mode are reported for ten ortho-substituted, six 2,6-disubstituted, and six miscellaneous polysubstituted aryltrimethyltin compounds. Although ¦ 1 J( 13 C 1H)¦ and ¦ 2 J( 119SnC 1H)¦ coupling constants are rather insensitive to substituent variation, tin methyl proton chemical shifts reflect the increasing inductive effects as methyl-, chloro-, fluoro-, and trifluoromethyl-groups are brought into juxtaposition with the trimethyltin moiety. Resonances in the natural-abundance carbon-13 NMR spectra for the tin derivatives are assigned on the basis of additivity relationships, proton undecoupled spectra, and relative magnitudes of ¦ J( 119Sn 13C)¦ and ¦ J( 13 C 19F)¦ coupling constants. Mutually deshielding γ-, δ-, and ϵ-effects in the carbon-13 chemical shifts of substituent carbons are rationalized in terms of steric crowding between the trimethyltin group and neighboring substituents. Deshieldings in ring carbons formally para- to conjugating substituents are discussed in terms of the steric inhibition of resonance model. Previous conclusions concerning lack of significant higher coordination at tin in aryltin derivatives bearing substituents with lone pair electrons are corroborated in this work.