SN2 Reactions of Nitranions with Benzyl Chlorides

Article abstract of DOI:10.1021/ja00323a029

The rates of S_N2 reactions of 19 nitranions with PhCH2Cl and 9 nitranions with m-CF3C6H4CH2Cl were measured in Me2SO at 25 deg C.Bronsted plots of log k vs. pK_HA for reactions of anion families derived from carbazoles, phenothiazines, and diphenylamines with PhCH2Cl are linear with slopes of 0.32-0.33.Extension of the carbazole and phenothiazine family lines, which are collinear, provided a reference line by which nucleophilicities of other nitranions could be assessed at constant basicity.Nitranions of varied structural types were found to have remarkably similar nucleophilicities when compared at the same basicities.Steric effects caused rates of reactions of ArAr'N(1-) ions and acetanilide ion to be retarded slightly and that of benzanilide ion to be retarded appreciably.Evidence is presented to show that nitranions, like carbanions, utilize the electron pair in a p orbital for bonding to an electrophile whereas pyridines utilize a nonbonded electron pair.Comparisons with literature data for neutral nitrigen nucleophiles, such as n-BuNH2 and PhNH2, indicate that they are 10-100 times more reactive than nitranion nucleophiles of comparable basicity.The order of nucleophilicities toward PhCH2Cl of anion families with different donor atoms when compared at the same basicity was found to be the following: 9-methylfluoredine ion family (25) > 2-naphthoxide ion family (3) > carbazole ion family (1.0).The results show that basicity is the primary factor in controlling nucleophilicities of nitranions, carbanions, and oxanions of diverse structural types in S_N2 reactions.Donor atom, solvation, and steric effects generally play a secondary role.