The cyclohexadienylidenemethanone radical cation is a more stable distonic isomer of ionized benzaldehyde

Quantum chemical calculations (G3B3 and B3LYP/6-311++G(d,p)) and tandem mass spectrometric experiments demonstrate the higher stability of 1,3-cyclohexadienylidenemethanone radical cation compared to ionized benzaldehyde. Characterized by a heat of formation of 833 kJ mol−1 (at 298 K), this ketene C7H6O+ isomer is found 43 kJ mol−1 more stable. It has been generated by ion/molecule reaction between ionized benzaldehyde and neutral methanol, a new example of proton transport catalysis tautomerization. The greater stability of the ketene ion is due to the low IE of the neutral (7.49 eV).