Solvolysis of benzylic chlorides with extended charge delocalization. ?-tert-butyl(2-naphthyl)methyl, 9-fluorenyl and monosubstituted benzhydryl chlorides

Abstract

Rate constants of solvolysis of a-tert-butyl(2-naphthyl)methyl chloride (1), 9-fluorenyl chloride (2) and a series of monosubstituted benzhydryl chlorides (3) in a wide range of solvents were measured. Grunwald-Winsteintype correlation analysis of log k for 2 and 3 against Y BnCl , with or without nucleophilicity N, yielded less satisfactory linear correlations than that against log k(1). A new scale of solvent ionizing power, Y xBnCl , for the correlation of solvolytic reactivities of benzylic chlorides with extended charge delocalization based on log k(1) was developed. Application to the mechanistic study suggested the solvolysis of 2 and 4-nitrobenzhydryl chloride were non-limiting. Hammett plots against ' constants exhibited more negative r values in less nucleophilic solvents. In a benzhydryl chloride containing a strong deactivating substituent, such as 4-nitro, the positive charge delocalizes mainly over the unsubstituted ring in the cationic transition state. The uneven charge distribution was also confirmed by Mulliken population analysis at the level of the RHF/6-31G * //RHF/3-21G

Effects of Ionic Liquids on the Nucleofugality of Chloride

“…The trends with changing solvent composition are the same, and the absolute values of the rate constants vary as predicted, with the greatest rate constant at a given solvent composition being observed for substrate 1a and the smallest rate constant observed in the case of the fluoride 1f . Note that the solvolysis rate constants in ethanol for all of the chlorides 1a – c , e , and f match those observed previously. − …”

“…The rate constant for the solvolysis of the chloride 1d in ethanol is consistent with that reported in the literature. 41,49,50 There is a notable increase in k 1 on addition of small proportions of salt 2 to the reaction mixture, followed by a decrease in the rate constant upon moving to higher proportions of ionic liquid 2. The maximum rate constant enhancement relative to ethanol, a factor of ca.…”

Solvolysis of 2-Aryl-2-chloro-4,4-dimethylpentanes. Confirmation of Validity of Brown−Okamoto σ+Constants

“…Very recently, however, the Liu group has reported that the F + value for the solvolysis of substituted benzhydryl chlorides changes from -4.10 to -4.26 in nucleophilic solvents (EtOH, MeOH, their aqueous mixtures, and aqueous acetone) to -4.93 (60T-40E) to -5.12 (80T-20E) and that the nucleophilic solvent participation decreases the sensitivity of solvolysis rates to σ + . 19 A similar trend has also been found in the solvolysis of 1-aryl-1-chloro-2,2-dimethylpropanes (1-aryl-1-tert-butylmethyl chlorides). 20 In Table 5 are summarized the F + values obtained for the systems 1 and 3 in eight solvents.…”

“…Liu examined eight solvents in the solvolysis of 2-aryl-2-chloroadamantanes and obtained respective ρ + values,2b but little attention has been paid to the relation between the substrate structure, solvent, and magnitude of the ρ + values. Very recently, however, the Liu group has reported that the ρ + value for the solvolysis of substituted benzhydryl chlorides changes from −4.10 to −4.26 in nucleophilic solvents (EtOH, MeOH, their aqueous mixtures, and aqueous acetone) to −4.93 (60T−40E) to −5.12 (80T−20E) and that the nucleophilic solvent participation decreases the sensitivity of solvolysis rates to σ + . A similar trend has also been found in the solvolysis of 1-aryl-1-chloro-2,2-dimethylpropanes (1-aryl-1- tert -butylmethyl chlorides)…”

“…Similar rationalizations for the downward deviation of the solvolysis rates in TFE for the Grunwald-Winstein relations of 2-oxo and 3-oxo bridgehead compounds have been presented. 22 By the same token, the recent data reported by Liu and co-workers 19 for the solvolysis of substituted benzhydryl chlorides appears to show that p-nitrobenzhydryl chloride solvolyzes approximately 2 times slower in 60T-40E than expected from the rate in 80E. 23 Comparison of Cation Stabilization by Solvent between 1 and 3.…”