e qt 0 adjacent to the sulfonyl sulfur, consistent with a cycle 104-5 transition state. The effectiveness of the tridentate ligand of 43 is dramatized 43, x = Br, I, s-, so-, SO,-, IO, IF,by characterizing the tridentate ligand as a host and the nonmetal X as a guest, using the nomenclature of Cram.37 The host is geometrically constrained to have almost the same geometry as it does in the host-guest complex, thus minimizing disadvantageous entropic factors in the formation of the complex while all the enthalpic advantages of the bonds around the central atom add to its stability. The host exerts a viselike grip on his guest.The existence of 10-S-3 sulfuranides, 103-4 sulfuranide oxides, and 1043-5 sulfuranide dioxides as single energy minimum ground-state structures indicates that other 104-3, 1 0 4 -4 , and 10-S-5 species may be energetically stable enough to exist as intermediates. It does not, however, prove the existence of an intermediate in any particular associative nucleophilic reaction a t sulfur, except the ones forming 1-3.Abstract: Acid-catalyzed (70% aqueous dioxane at 0 "C) and thermal rearrangement (95% ethanol at 80 "C) of 2,2'-hydrazonaphthalene (1) into 2,2'-diamino-l,l'-binaphthyl (2) have been shown to be concerted, [3,3]-sigmatropic shifts. This was accomplished by measuring the nitrogen and carbon kinetic isotope effects (KIE), for which purpose mixtures of 1 with [IsN,15N']1 and [ l,l'-13Cz]l were used. KIE were calculated from whole-molecule mass ratios, measured by multiscan mass spectrometry, in the bis(trifluoroacety1) derivative of product 2, isolated after low and high conversions. The results (averaged) were, for two isotopic atoms, k(I4N)/k(l5N) = 1.0904, k(1zC)/k(13C) = 1.0086 in the one-proton, acid-catalyzed rearrangement and 1.061 1 and 1.0182, resFtively, in the neutral, thermal rearrangement. These results indicate that although the rearrangements are concereted processes, the breaking of the N-N bond and the forming of the C-C bond proceed to different extents in the transition states. Furthermore, the difference in the timing of these events is greater in the acid-catalyzed than in the thermal rearrangement, a difference which may be attributable to earlier C-C bonding in the polar transition state of the former.Among benzidine rearrangements5-I5 those of hydrazoarenes which contain the 2-naphthyl group constitute a unique class. First, in acid-catalyzed rearrangements in the usual solvents (aqueous ethanol or aqueous dioxane), they undergo almost complete o,o'-bonding with little or no concommitant disprot Texas Tech University. *Rutgers University. (1) Previous paper: Shine, H. J.; Park, K. H.; Brownawell, M.; San Filippo, J., Jr.