Folded conformations. Part VI. An NMR spectroscopic study of the preferred solution conformation of N,N′‐[bis(α‐tosylbenzyl)]urea

Abstract

AbstractComparison of NMR spectral data of a number of N‐tosylalkyl‐ and N,N′‐bis(tosylalkyl)ureas reveals that the methyl protons of the tosyl moiety and the α‐sulfonyl alkyl proton in the N,N′‐[bis(α‐tosylbenzyl)]ureas 1‐3 resonate at unusually high fields. The presence of both sulfonyl groups and the aromatic rings of the benzyl moieties are prerequisites for the observation of appreciable upfield shifts. Evidence is presented that intramolecular shielding phenomena are involved. It is proposed that 1‐3 in solution predominantly adopt conformations in which each tosyl methyl group is positioned in the shielding region of the phenyl ring of the most remote benzyl group.