104292-40-2Relevant articles and documents
Rate-Equilibrium Relationships for Reactions of Families of Carbanion Nucleophiles with N-Benzyl-N,N-dimethylanilinium Cations and with Alkyl Chlorides, Bromides, and Iodides
Bordwell, Frederick G.,Hughes, David L.
, p. 7300 - 7309 (2007/10/02)
Rates of reaction of a family of 9-methylfluorenide anions, 9-MeFl-, with 15 substituted N-benzyl-N,N-dimethylanilinium cations, GC6H4CH2N(Me)2C6H4Y+, were measured in a 0.8 M KNO3 solution of Me2SO at 25 deg C.Substitution in the benzyl moiety produced a U-shaped Hammett plot, with m-CN reacting 9- to 15-fold faster than H and p-MeO reacting 1.5- to 3-fold faster than H, depending on the basicity of the 9-RFl- ion.Broensted ΒNu values obtained by varying nucleophile basicity in the 9-MeFl- ion family were 0.28 for N-(p-methoxybenzyl)-N,N-dimethylanilinium ion, 0.33 for N-benzyl-N,N-dimethylanilinium ion, and 0.39 for N-(m-cyanobenzyl)-N,N-dimethylanilinium ion.These βNu values were unaffected by substitution in the aniline portion of the substrate.Hammett pLg values were obtained by substitution of m-Cl, p-Br, H, p-Me and p-MeO groups (Y) in the dimethylaniline leaving group; pLg values were all near 2.0 and were insensitive to the basicity of the attacking nucleophile and the substituent G in the benzyl group of the substrate. βNu values for families of 9-RFl- ions reacting with ArCH2X, n-BuX, and CNCH2X also remained constant as the leaving group, X, was changed (Cl, Br, and I) for a given substrate and when the donor atom was changed along the series C-, N-, O-, and S-.These results indicate that there is no direct relationship between the size of βNu and the extent of bond making or bond breaking in the transition state for SN2 reactions, as has been generally assumed in theoretical attempts to rationalize the effects of structural variations on rate.It is suggested that SN2 reactions occur in two stages.The size of βNu is determined in the first stage where an ion-dipole complex is formed.The rate is determined largely in the second stage where bonds are formed and cleaved and where molecular and solvent reorganization occurs.
