Ring-size effects on the ionization potentials of N-substituted azacycloalkanes

Abstract

The ionization potential of the lone-pair electrons of nitrogen has been determined for N-methyl- and N-tosyl-azacycloalkanes by means of gas-phase u.v. photoelectron spectroscopy. The cyclic compounds examined contain small, common, medium, and large-membered rings. The ionization potentials are affected by conformational features and, in particular, by the strain present in the ring. More precisely, the IPs reflect changes of hybridization of the nitrogen Ione pair upon varying the ring size, whereby a lower or higher energy is required for the ionization process of the cyclic compounds relative to a series of open-chain alkyl amines taken as reference. Steric inhibition of resonance by the N-tosyl substituent takes place in the case of the strained small rings.