Experimental and Computational Study of Methylphenylvinylidene and Its Rearrangements

Author (Your Name)

Xi YangFollow

Date of Award

2016

Document Type

Honors Thesis (Open Access)

Department

Colby College. Chemistry Dept.

Advisor(s)

Dasan M. Thamattoor

Second Advisor

Rebecca R. Conry

Abstract

In this study, the synthesis and properties were explored of the compound methylphenylvinylidene (MPV), a vinylidene carbene with methyl and phenyl groups as substituents. A phenanthrene-based precursor, 1-(1-phenylethylidene)-1a,9b-dihydro-1H-cyclopropa[l]phenanthrene, was synthesized in three steps and was subjected to photolysis in C₆D₆ at ambient temperature. During photolysis, the MPV carbene rearranged into 1-phenylpropyne via a 1,2-phenyl shift, instead of 1,2-methyl shift, confirmed by photolysis of ¹³C-labeled precursor. This experimental result is consistent with computational results using the CCSD(T)/cc-pVTZ//B3LYP/6-31+G* method. The calculations suggest that the 1,2-phenyl shift in singlet carbene requires 3.8 kcal/mol to overcome the barrier, whereas the 1,2-methyl shift needs 11.9 kcal/mol. The generation of MPV carbene was confirmed by trapping with cyclohexene, which gave a carbene-alkene cycloadduct, with a yield of 1.5%. The identity of the trapped product was confirmed by the authentic sample of the trapped adduct, which was synthesized in three steps starting from cyclohexene. Additionally, upon photolysis, 11% of the precursor rearranged into a mixture of E- and Z- cycloheptatriene derivatives.

Keywords

Carbene

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