Kinetic studies for the reactions of phenacyl p-bromobenzenesulfonate with substituted pyridines under high pressures

p-Hydroxyphenacyl photoremovable protecting groups — Robust photochemistry despite substituent diversity

“…The general methods of Finkelstein 34 and Yoh et al 35 were utilized with modifications. A 50 mL round-bottom flask was charged with 4-(2-chloroacetyl)-3-methoxyphenyl pivalate ( 30c , 500 mg, 1.8 mmol) and NaBr (1.08 g, 10.5 mmol).…”

Activation and Reaction Volumes in Solution. 3

“…The decomposition of nitroso dimers (entries 562 and 563) is retarded by pressure, as should be expected from bond cleavage reactions; the disappearance of the formal charges may also have played a role. 545, 546 Neuman 501 has contributed further insights into the decomposition of azo compounds (entries [564][565][566][567][568][569]: it is now clear that while one bond breaks initially, diffusion to separate radicals is a critical part of the reaction. This causes the positive activation volumes to be larger than in the case of most single bond scission processes; they contrast with peroxide decomposition 549 (entries 570-576; no return, early transition states).…”

“…Yoh's group has reported the reactions of variously substituted pyridines in acetonitrile, over a range of temperatures. These authors found that ρ steadily decreases as the pressure is raised, and attributed this fact to the increase in density of the solvent, and hence, to decreased electrostriction (the opposite is true for the phenacyl sulfonates). − A comparison with the known pressure effects on the corresponding benzyl sulfonates led the authors to conclude that the former have “more S N 2 character” in the transition state.…”