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Singlet−Triplet Splittings and 1,2-Hydrogen Shift Barriers for Methylphenylborenide, Methylphenylcarbene, and Methylphenylnitrenium in the Gas Phase and Solution. What a Difference a Charge Makes

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journal contribution
posted on 17.12.1997 by Christopher J. Cramer, Donald G. Truhlar, Daniel E. Falvey
In the isoelectronic series methylphenylborenide, methylphenylcarbene, and methylphenylnitrenium, fundamental differences are predicted for singlet state geometries, singlet−triplet state splittings, barriers to singlet 1,2-hydrogen migration, and sensitivity of 1,2-hydrogen migration to solvent effects in n-heptane and acetonitrile. We conclude that isoelectronic analogies are dangerous for systems having different formal charges, and that the interaction of the divalent center with a conjugating substituent is very sensitive to the electron donating or withdrawing nature (and power) of the hypovalent atom. Solvent effects on the singlet−triplet splitting result from static polarity differences whereas the solvent effects on 1,2-hydrogen migration result primarily from polarizability differences. For the experimentally characterized carbene case, extensive comparison of calculated and measured results is provided.