Time-resolved infrared study of the photoinduced Wolff rearrangement and carbene intermediates

To clarify the role of diazocarbonyl excited states in photoinduced Wolff rearrangement chemistry, time-resolved infrared (TRIR) spectroscopy has been used to study a series of acyclic and cyclic diazocarbonyl compounds and the subsequently produced carbenes. TRIR spectroscopic analysis of the growth rates of the corresponding ketene rearrangement products provided direct evidence to support the hypothesis that the reaction pathway of Wolff rearrangement is strongly influenced by the conformation of the diazo precursor.; The solvent dependence of the 2-naphthyl(carbomethoxy)carbene singlet/triplet energy gap has been examined by TRIR spectroscopy and computational methods. The ground state of 2-naphthyl(carbomethoxy)carbene changes from the triplet state in hexane to the singlet state in acetonitrile. Preferential stabilization of the singlet carbene is the result of its increased dipole moment in polar solvents. This is consistent with B3LYP calculations.; The effect of aromatic substitution on the singlet/triplet energy gap in substituted phenyl(carbomethoxy)carbene(X-Ph-C-COOCH₃, PCC) has been explored by TRIR spectroscopy and compared to gas-phase computational results. The absence of solvent perturbation in the TRIR spectra of p-N(CH₃)₂-PCC and parent PCC is consistent with the ground states lying >±2 kcal/mol from the next available electronic state, in line with the computational results. The observation of solvent perturbation in the TRIR spectra of p-OCH ₃-PCC and p-CH₃-PCC implies that their ground states lie <±1 kcal/mol from their next available electronic state. TRIR spectroscopic study and comparison with the computational results of meta-substituted PCC species are also presented.; Photoinduced Wolff rearrangement of 2-diazo-N,N-dimethyl phenyl acetamide has been studied by TRIR spectroscopy in Freon-113. NMR analysis of this diazoamide in acetonitrile with varying amounts methanol showed that the β-lactam product is formed only from the corresponding carbene and not from a diazoamide excited state.; Preliminary results concerning a new diazeniumdiolate coupling methodology and TRIR spectroscopic studies of benzoyl nitrene and 2-diazo-1,3-diphenyl-1,3-propanedione are also discussed.