6013-94-1Relevant articles and documents
Solvolysis of 1-alkyl-1-chloro-1-(4-methyl)phenylmethanes. Nucleophilic solvent intervention and extended YBnCl scale
Liu, Kwang-Ting,Chang, Lih-Wie,Yu, Der-Gann,Chen, Pang-Shao,Fan, Ju-Ta
, p. 879 - 884 (2007/10/03)
The solvolysis of 1-alkyl-1-chloro-1-(4-methyl)phenylmethanes (4a-d) in aqueous acetone, aqueous ethanol, aqueous methanol and ethanol-trifluoroethanol was studied. Grunwald-Winstein-type correlation analysis using the YBnCl scale suggests significant nucleophilic solvent intervention in the case of 1-chloro-1-(4-methyl)phenylethane (4a). Increasing bulkiness of the 1-alkyl substituent from methyl (4a) to ethyl (4b), to isopropyl (4c) and to tert-butyl (4d) resulted in a gradual change to limiting SN1 mechanisms. The observed excellent linear correlations with YBnCl and the good solubility in high-water-containing binary solvents made 4d a suitable reference standard for deriving more YBnCl values. A positive azide salt effect was realized in the solvolysis of 4a but not 4d. A small decrease in the β-deuterium kinetic isotope effect from 4a to 1-chloro-1-(4-methoxyphenyl)propane (5) suggested the presence of additional stabilization of the benzylic cationic transition state. However, no relationship between k(CH3)/k(CD3) and the solvent effect was found. The superiority of employing the YBnCl scale over the combination of YCl and I scales in the mehanistic study was observed.
Anodic Oxidation of α-Substituted p-Xylenes. Electronic and Stereoelectronic Effects of α-Substituents in the Deprotonation of Alkylaromatic Radical Cations
Baciocchi, Enrico,Mattioli, Mario,Romano, Roberta,Ruzziconi, Renzo
, p. 7154 - 7160 (2007/10/02)
The effect of α-substituents on the deprotonation rate from the benzylic position of alkylaromatic radical cations, k(CH2Z)/k(CH3), has been investigated by determining the intramolecular selectivity in the anodic oxidation in acetic acid of a α-Z-substituted p-xylenes 1 (Z = H, OMe, OH, Me, tert-butyl, OAc, COOMe, CN), 5,6-dimethylindan 4 (R = H), and 2,2,5,6-tetramethylindan 4 (R = Me).Some oxidations induced by CAN have also been carried out.It has been found that, with the exception of when Z = tert-butyl, the deprotonation rate of 1.+ is always faster from the CH2Z group than from the CH3 group, independently of the electron-donating or electron-withdrawing nature of Z.The electron-donating groups (OH, OMe, Me), however, exert a larger effect than the electron-withdrawing ones (COOMe, CN).The negligible deprotonation rate from CH2-t-Bu has been ascribed to stereoelectronic effects (the bulky tert-butyl group does not allow the C-H bonds to be collinear with the ?-system), the suggestion being nicely confirmed by the observation that the deprotonation rate from the position 1(3), relative to that from the 5(6)-methyl group, is almost identical in the radical cations of 4 (R = H and Me).The effect of the other α-substituents is mainly of electronic nature and has been rationalized on the basis of a variable transition-state structure for the deprotonation process.It is suggested that with +R groups most of the charge, in the transition state, has been transferred to the Cα-H bond where it can be stabilized by the α-substituent.With electron-withdrawing groups less charge transfer has taken place and the rate-enhancing effects of these groups is ascribed to their capability to significantly decrease the strength of the Cα-H bond.
CHROMATOGRAPHIC RESOLUTION OF ALKYL ARYL CARBINOLS ON A SILICA-SUPPORTED QUININE CHIRAL STATIONARY PHASE
Pini, Dario,Rosini, Carlo,Bertucci, Carlo,Altemura, Paolo,Salvadori, Piero
, p. 603 - 606 (2007/10/02)
Several alkyl aryl carbinols can be separated in enantiomers by liquid chromatography upon a new chiral support, prepared by reaction of γ-mercaptopropylsilanized silica with quinine.From the elution order obtained by means of a circular dichroism detecto
