VICINAL N,N INTERACTIONS IN N-CHLORO SUBSTITUTED DIAZIRIDINES AND OXAZIRIDINES - PHOTOELECTRON-SPECTRA AND ELECTRONIC-STRUCTURES

The He(I) photoelectron spectra of five bicyclic N-chlorodiaziridines (6-10) and three N-chlorooxaziridines (14-16), as well as of the corresponding N-H compounds (1-5 and 11,13), have been recorded and analysed using AM1 calculations. The N-chlorodiaziridines show exo-endo isomerism; however, only one endo isomer (10a) is sufficiently stable for the measurement. The N-chlorooxaziridines are more stable than their N-H precursors. The compounds are characterized by three non-bonding orbitals n(NN)(+), n(NN)(-) and n(Cl) (N-chlorodiaziridines); n(NO)(-) n(Cl) and n(O) (N-chlorooxaziridines). These orbitals give rise to the first three ionization bands of the compounds. The energy separation of the two n(NN) MOs of the exo isomers 6b-10b (Delta epsilon approximate to 0.3 eV) is smaller than in the corresponding N-H compounds 1-5 (Delta epsilon approximate to 0.6 eV), while in the endo isomer 10a (Delta epsilon approximate to 1.2 eV) it is larger than in 5. In the oxaziridines, replacement of the hydrogen atom by a chlorine atom leads to a small stabilization of the n(O) orbital. These findings can be interpreted by vicinal n(X)/sigma(N-Hal)* interactions (X = N or O).