THE BENZIDINE AND DIPHENYLINE REARRANGEMENTS REVISITED - 1-C-14 AND 1,1'-C-13(2) KINETIC ISOTOPE EFFECTS, TRANSITION-STATE DIFFERENCES, ANDCOUPLED MOTION IN A 10-ATOM SIGMATROPIC REARRANGEMENT

KIE were measured for 1-C-14- and 1,1'-C-13(2)-labeling in the acid-ca talyzed rearrangement of hydrazobenzene (1) to benzidine (2) and diphe nyline (3). Small KIE were found for forming 2, but none were found fo r the formation of 3. The results are consistent with concerted format ion of 2 and nonconcerted formation of 3. KIE were remeasured for 4-C- 14-, 4,4'-C-13(2-)-, and N-15,N-15'-labeling and were found to differ in magnitude from KIE reported earlier. The results are, nevertheless, consistent with the concerted formation of 2 and nonconcerted formati on of 3. The differences in transition states for these two processes are discussed. Quantitative measurements of product distributions ave 85% 2 and 15% 3.