Solvolysis of benzylic chlorides with extended charge delocalization. α-tert-butyl(2-naphthyl)methyl, 9-fluorenyl and monosubstituted benzhydryl chlorides
✍ Scribed by Kwang-Ting Liu; Yen-Shyi Lin; Meng-Lin Tsao
- Book ID
- 101286264
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 133 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0894-3230
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✦ Synopsis
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 (*) basis set for cations. Comparison of the results of correlation analysis using the equation log(k/k 0 ) = mY vs the equation log(k/k 0 ) = mY hI, and using the equation log(k/k 0 ) = mY lN vs the equation log(k/k 0 ) = mY lN hI indicated the use of Y BnCl or Y xBnCl could give a better understanding of solvolytic mechanisms than the combinatorial use of Y Cl and I.