ULTRAVIOLET PHOTOELECTRON, ELECTRON TRANSMISSION AND AB-INITIO STUDY OF THE FACTORS DETERMINING THE STABILITY OF IMINES

The electronic structure of several alkyl-, N-bis(trimethylsilyl)methy l- (BTMSM), and C-phenyl-substituted imines 1-11 have been determined by ab initio 3-21 G calculations. The calculations reproduce with goo d accuracy the available geometry of methylenimine, 1, obtained by mic rowave spectroscopy(1) and ab initio 6-31 G* calculations(2) as well as the outermost energy levels experimentally determined by ultraviole t photoelectron spectroscopy for several derivatives. The analysis of the results of the calculations indicate that alkyl substitution of 1 at the nitrogen atom reduces the charge separation at the double bond increasing stabilisation, while substitution at the carbon atom has th e opposite effect. Steric hindrance of the substituent(s) and the ener gy gaps between filled (nitrogen lone pair, HOMO and pi(CN)) and virtu al (pi(CN)) orbitals play a secondary role on stability. All the BTMS M and phenyl derivatives studied are stable in air at room temperature irrespective of other substituents present. Our analysis indicates th at these substituents change the energy. ordering and localisation pro perties of the valence MOs. In particular, the nitrogen lone pair orbi tal is no longer the HOMO.