Properties and Exciting Facts About C8H5BrS

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Rate coefficients for detriation of benzothiophen, specifically labelled with tritium at each position, have been measured in anhydrous trifluoroacetic acid, and, for <2-3H>benzothiophen, in a range of trifluoroacetic acid-acetic acid mixtures, all at 70 deg C.The dependence of rate upon acidity is consistent with the effect of hydrogen bonding between sulphur and trifluoroacetic acid, as found previously for other sulphur-containing heterocycles.Partial rate factors, corrected for the effect of hydrogen bonding are (positions in parentheses): 8.84 * 105 (2); 1.18 * 106 (3); 360 (4); 13200 (5); 16200 (6); and 26.2 (7); the corresponding ?+ values are -0.68, -0.695, -0.29, -0.47, -0.48, and -0.16.The positional reactivity order is the same as found in pyrolysis of 1-arylethyl acetates, and solvolysis of 1-arylethyl chlorides, but the ?+ values are more negative due to the greater demand for resonance stabilization of the transition states in hydrogen exchange.Comparison of the 2- : 3-isomer ratios in various substitutions leads to the unexpected conclusion that substitution at the 2-position is subject to steric effects, probably due to the proximity of the sulphur d-orbitals.