Hydrogen bonds involving polar CH groups. Part 10. Intramolecular hydrogen bonds in 1-(ω-substituted-alkyl) bis(phenylsulphonyl)methanes

Abstract

Intramolecular hydrogen bonds involving the polar methine group have been detected by ¹H n.m.r. spectroscopy in dichloro[²H₂]methane in 1-(ω-methoxyalkyl)- and 1-(ω-dialkylaminoalkyl)-bis(phenylsulphonyl)methanes. Dialkylamino groups are more effective donors than methoxy, and interactions are maximised when a five- or ideally a six-membered ring can be formed. The optimum compounds, having a methyl group in the side-chain to reduce conformational mobility, show ¹H n.m.r. downfield shifts of ca. 1.9 p.p.m. relative to a reference compound, increasing to 2.2 p.p.m. on lowering the temperature to –40 °C. Downfield shifts are generally larger than for similarly substituted 1,3-dithiane 1,1,3,3-tetraoxides; the phenyl groups appear to reduce further the conformational mobility of the side-chain. Interactions are uncoupled partly by acetonitrile and pyridine, and fully by trifluoroacetic acid. Some i.r. evidence for an interaction is also presented.