Benzocyclobutene: The impact of fusing a strained ring onto benzene

The gas-phase acidities of the two aromatic sites in benzocyclobutene were measured in a Fourier transform mass spectrometer using a kinetic technique (i.e., the DePuy method). Fusion of a cyclobutane ring onto benzene is fou nd to have a slight acidifying effect at the alpha-position (3.2 +/- 1.7 kc al mol(-1)) and little, if any, influence on the beta-site (0.8 +/- 1.9 kca l mol(-1)). Energetic data (Delta H degrees(acid) = 386.2 +/- 3.0 kcal mol( -1), EA = 0.84 +/- 0.11 eV, and C-H BDE = 92 +/- 4 kcal mol(-1)) for the be nzylic position were obtained via the bracketing technique and application of a thermodynamic cycle. Differences in the reactivities of the three conj ugate bases also were explored. Ab initio and density functional theory cal culations were carried out to provide geometries, energies, and insights in to the carbanions' electronic structures.