Photoelectron spectra and electronic structure of substituted aziridines Part 2. Photoelectron spectroscopic and quantum chemical studies of some donor/acceptor substituted aziridines

The He(I) PE spectra of 2-methylaziridine (1), 2,2-dimethylaziridine (2), 1-chloro-2-methylaziridine (3), 1-chloro-2,2-dimethylaziridine (4), 2-methyl-1-nitrosoaziridine (5), 2,2-dimethyl-1-nitrosoaziridine (6), 1-cyano-2,2-dimethylaziridine (7) and 2-cyanoaziridine (8) have been analysed using MNDO and AM1 calculations. The variation of the nitrogen lone-pair and the Walsh-type orbitals ωA and ωS with substitution is discussed. The results are compared with the corresponding data for aziridine (9), 1-methylaziridine (10), 1-chloroaziridine (11) and 1-nitrosoaziridine (12). The cyano compound 7 shows the same sequence of the orbitals nN, ωS and ωA as the 1-chloroaziridine derivative 4. Donor/acceptor substituted aziridines like 3, 4, 5, 6 and 7 behave like push/pull systems. In these compounds electron density is transferred from the donor to the acceptor group. The orbitals effecting this transfer are stabilized while the other ones are destabilized. In the methyl derivatives 3, 4 and 7, ωA is stabilized by the methylation of the three-membered ring, while in the nitroso compounds 5 and 6 ωS is affected in the same way.