Geometry and electronic structure of silylated hydroxylamine and carbamic acid derivatives

The He(I) and He(II) photoelectron spectra of silylated nitrogen and oxygen compounds were recorded in order to study their electronic structure and g eometry. The X-ray crystal structure of N-trimethylsilyl O-tert-butyl carba mate is given. Ab initio Hartree-Fock calculations were also carried out to obtain theoretical geometries of the compounds and to help the assignments of their photoelectron spectra by means of Koopmans' theorem. Our results show that the planar/pyramidal spatial arrangements around nitrogen in the investigated compounds can be rationalised by the negative hyperconjugative effect of silyl group(s), by electrostatic effects and by the lone-pair re pulsion of the neighbouring nitrogen and oxygen atoms. The considerable dis tortions in geometry cause only small variations in the electronic structur e, and there are relatively small energy differences (about 15-20 kJ mol(-1 )) between the planar and the pyramidal conformers. These conclusions can a lso be applied for silylated oxygen compounds. (C) 1999 Elsevier Science S. A. All rights reserved.