1- and 3-Nitreno-2-naphthylcarbenes. A Combined Experimental and Computational Study

Abstract

Abstract The structures, energies, and thermal stabilities of E and Z isomers of a singlet, a triplet, and a quintet states of naphthalene bearing nitrene and carbene units on adjacent (1,2- and 3,2-) positions were examined by DFT methods. For both 1,2- and 3,2-isomers, singlet quinoidal diradicals were predicted to be the ground state with the corresponding triplet state lying slightly higher in energy. The quintet state of the 1,2-isomer was found to lie approximately 30 kcal mol−1 (1 kcal = 4.184 kJ) above the ground state, while that of the 3,2-isomer was predicted to lie only 9 kcal mol−1 above the ground state. This difference is discussed in terms of loss of energy due to aromaticity between the two isomers. Thermal stability of the ground state in terms of ring-opening and -closure reactions indicated that both isomers prefer to decay by the latter process forming naphtho[b]azetes. Attempts to generate and characterize the ground state quionoidal diradical by matrix IR spectroscopic methods in Ar at low temperature all resulted in the detection of the azete.