Origin of significant solvent effects on ~1J(CC) spin-spin coupling in some acetylenes: Hydrogen bonding and solvent polarity

摘要

It is demonstrated that some acetylenes, those of the R-C-CH structure, display anomalously high sensitivity to solvent effects of their ~1J(C-C) coupling while R-C-CR acetylenes fail to show that. The solvent-induced variation in the latter coupling does not exceed 3 Hz; this seems to be the upper limit of variation of any J(CC) and J(CH) coupling in the molecular system studied which included: acetylene (in 13 solvents), phenylacetylene (in 12 solvents), 1-phenylpropyne, and 2-hexyne (two solvents each), and the only exceptions are ~1J(C-C) in acetylene, which is shown to vary within about 13 Hz, and that in phenylacetylene where the range amounts to about 8 Hz. These apparent anomalies are explained in the present study in terms of two effects of prime importance, solvent polarity and the solute-to-solvent hydrogen bonds where the CH moiety in R-C-CH acetylenes acts as a donor of hydrogen bonds to acceptor sites in the solvent concerned.