The benzidine and diphenyline rearrangements revisited. 1-14C and 1,1′-13C2 kinetic isotope effects, transition state differences, and coupled motion in a 10-atom sigmatropic rearrangement

Article abstract of DOI:10.1021/ja00065a018

KIE were measured for 1-¹⁴C-and 1,1′-¹³C₂-labeling in the acid-catalyzed rearrangement of hydrazobenzene (1) to benzidine (2) and diphenyline (3). Small KIE were found for forming 2, but none were found for the formation of 3. The results are consistent with concerted formation of 2 and nonconcerted formation of 3. KIE were remeasured for 4-¹⁴C-, 4,4′-¹³C₂-, and ¹⁵N,¹⁵N′-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 formation of 3. The differences in transition states for these two processes are discussed. Quantitative measurements of product distributions gave 85% 2 and 15% 3.