N.m.r. spectra of cyclic amines. II—Factors influencing the chemical shifts of α‐protons in aziridines

Proton magnetic resonance spectra of trans and cis‐2,3‐diphenylaziridine (1 and 2) and their N‐ethyl derivatives 3 and 4 were measured in carbon tetrachloride, chloroform, and benzene‐d₆ at low temperatures (1 and 3) and in dry conditions (1 and 2). On the basis of these results it was concluded that an N‐ethyl group exerts a shielding influence on a cis ring proton and a deshielding influence on a trans ring proton. From results obtained by measuring the ¹H n.m.r. spectra of 1–4 in deuterochlorofom‐trifluoroacetic acid it was derived that the lone pair of the aziridine nitrogen exerts a shielding influence on cis related ring hydrogens. In most N‐alkylaziridines the effect of the N‐alkyl group predominates.