In order to explore the thermodynamical effects of substituents on stability and reactivity of triplet diphenylcarbenes, triplet bis (2,6- dimethy-4-methoxy) phenylcarbene (2c) bearing strong electron-donating methoxy group at the para position was generated by irradiation of bis (2,6-dimethyl-4-methoxy)-phenyldiazomethane (1c), and studied by means of electron paramagnetic resonance (EPR) and UV/vis spectroscopy at 77 K. We measured the rate constant, which obeyed the second order decay, and lifetime by laser flash photolysis (LFP) in degassed benzene at room temperature. It was revealed that the reactivity of bis(2,6- dimethyl-4-methoxyphenyl) carbene (2c) increased sharply owing to the strongly electron-donating methoxy group at the para position. Product analysis showed that bis(2,6-dimethyl-4-methoxyphenyl)carbene (2c) decayed besides dimerization to form tetra (aryl) ethylene (3c) or attacked at an o-methyl group to afford 1,2-dihydrobenzocyclobutenes (4c) like the para-unsubstituent bis (2,6-dimethylphenyl) carbene (2b), and also generated 3,6-dimethyl-1,4a, 8-trimethyl-4a, 10- dihydroanthracene (5c) and 2,2'-di(2,6-dimethyl-4-methoxybenzyl)-3,3'- dimethyl-5,5'-dimethoxystilbene (6c) by attacking on the o-methyl group in solution because of electron-donating effect of the methoxy group at the para position.

Key words: CARBENE, SUBSTITUENT EFFECT, STABILITY, PR