A photoionization and molecular orbital study of cyclobutanol and cyclobutylamine radical cations

Abstract

Dissociative ionization of cyclobutanol, 1 and cyclobutylamine, 2 to produce [CH 2CHX] ·+ + C 2H 4 (X  OH or NH 2) has been studied by photoionization and ab initio molecular orbital calculations. The latter reveal that ionized cyclobutanol and cyclobutylamine are not minimia in their respective potential energy surfaces. It is further concluded that ionization of 1 and 2 leads to the corresponding distonic species [CH 2CH 2CH 2CHX] ·+. From the measurement of the first dissociation onset, an accurate determination of the heats of formation of [CH 2CHX] ·+ ions is made, i.e. Δ H° f,300[CH 2CHOH] &,middot;+ = 768 ± 5kJ mol −1 and Δ H° f,300[CH 2CHNH 2] &,middot;+ = 838 ± 5kJmol −1, after correction for the thermal energy of the precursor molecules. By combining calculations (at the MP2/6-311G **//UHF/6-31G * + ZPE level) and experiments, heats of formation of the distonic ions have been estimated: Δ H° f,300[CH 2CH 2CH 2CHOH] ·+ = 733kJmol −1 and Δ H° f300[CH 2CH 2CH 2CHNH 2] ·+ = 792kJmol −1, with a probable error of ±12kJmol −1.