The substitution structure of ethyleneimine

The substitution structure (rs) of ethyleneimine (aziridine) has been found by analysis of microwave gas spectra of the parent molecule and of the necessary number (5) of mono-isotopically substituted species, all of which were chemically enriched. Two coordinates (<0.1 A) had to be derived using the conditions Σmici = Σmibici = 0. Data from microwave spectra of two double-isotopically substituted species [1-D]-, [1−15N]-ethyleneimine, and [2,2'-D2]-ethyleneimine were applied as a further check. The agreement was satisfactory. In the resulting rs structure the C-C distance is shorter than the C-N distance, in accordance with the larger nuclear charge of nitrogen compared to carbon, but qualitatively disagreeing with the results of earlier investigations. Also, the plane defined by H(2), C(2), H(2') is not perpendicular to the N(1), C(2), C(3) plane as assumed earlier. The former plane forms and angle of 87° with the latter which, however, almost exactly bisects the HCH angle. The CH2 groups may, therefore, be described as slightly “twisted”.