A theoretical re-evaluation of the heat of formation of phenylcarbene

Singlet–triplet separation and heat of formation of phenylcarbene were calculated by using the B3LYP, RCCSD(T), G2M, G3, CASSCF, CASPT2 and MRCI methods. Our calculated values are 2.5±1 kcal/mol for the singlet–triplet splitting energy, 113.5±1 kcal/mol for the standard heat of formation (ΔHf 2980) of singlet phenylcarbene, and 111.0±2 kcal/mol for the standard heat of formation of triplet phenylcarbene. While the singlet–triplet separation is in good agreement with previous theoretical and experimental data, the standard heat of formation of triplet phenylcarbene is about 7–8 kcal/mol higher than the experimental value (103.8±2.2 kcal/mol by Squires et al. [J. Chem. Soc., Perkin Trans. 2 (1999) 2249]).