Substituent Effect on the Gas Phase Basicity of α-t-Butylstyrene. Coplanarity and Resonance Demand of a Benzylic Carbocation

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Abstract
Gas phase basicities of α-t-butylstyrenes were determined based on the proton transfer equilibria. The substituent effect on the basicity has been analyzed by means of the LArSR Eq. 1, providing a ρ of −12.5 and an r of 0.86. The reduced r value relative to that for α-methylstyrene may be attributed to sterically twisting out of the coplanarity of benzene π-system in the conjugate acid ion, α-t-butyl-α-methylbenzyl cation.