Du L, Lan X, Phillips DL, Coldren WH, Hadad CM, Yang X, Thamattoor DM. Direct Observation of an Alkylidenecarbene by Ultrafast Transient Absorption Spectroscopy.
J Phys Chem A 2018;
122:6852-6855. [PMID:
30067896 DOI:
10.1021/acs.jpca.8b06118]
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Abstract
Singlet α-methylbenzylidenecarbene has been detected and characterized for the first time by femtosecond transient absorption (fs-TA) spectroscopy. The carbene was generated by photolysis of the hydrocarbon precursor, 1-(1-phenylethylidene)-1a,9b-dihydro-1 H-cyclopropa[ l]-phenanthrene, in acetonitrile. The photolysis initially forms the singlet excited state of the precursor which then extrudes α-methylbenzylidenecarbene in 4.0 ps. The decay of α-methylbenzylidenecarbene, which was previously shown to rearrange into phenylpropyne by a 1,2-phenyl shift, occurred over 13.3 ps. Computed spectra at the TD-B3LYP/6-311+G** level of theory are consistent with the experimental observations. CASSCF(10,10)/6-311+G** calculations, using one of the carbene conformers as a model, indicated that the reference wave function is dominated by a closed-shell description.
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