ISSN:
0894-3230
Keywords:
SN1 solvolysis
;
carbocation
;
Grunwald-Winstein relationship
;
solvent effect
;
solvation
;
Chemistry
;
Theoretical, Physical and Computational Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
---The rates of solvolysis in various solvents at 25 °C were determined for five tertiary alkyl chlorides: 2-chloro-2,4,4-trimethylpentane (4), 2-chloro-2,4-dimethylpentane, 2-chloro-2-methylpentane, 1-chloro-1,3,3-trimethylcyclopentane (7) and 1-chloro-1-methylcyclopentane. The rate data were analysed on the basis of the original and extended Grunwald-Winstein-type equation [log(k/k0)=mYCl+c and log(k/k0)=lNT+mYCl+c] and the results were compared with those reported for 2-chloro-2-methylpropane (1) and 2-chloro-2,3,3-trimethylbutane (3). The rate data for 4 in 18 solvents give an excellent correlation with l=0·00±0·02 and m=0·74±0·01. The neopentyl group in 4 more effectively shields the rear-side of the reaction center than the tert-butyl group in 3 that is correlated by l=0·10±0·04 and m=0·81±0·04. The rate ratio between 4 and 1 at 25 °C is 275 in TFE and predicted to increase to 950 in TFA. The previous 4/1 rate ratio of 21 in 80% ethanol evidently underestimates the B-strain effect on the solvolysis rate of 4 by a factor of at least 40. The remote methyl groups in 7 works to increase rear-side shielding without increasing B-strain. The marked difference in the effect of the remote methyl groups between 4 and 7 suggests that the leaving chloride ion in 4 takes a locus that is nearly antiperiplanar to the tert-butyl group. © 1997 John Wiley & Sons, Ltd.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
Permalink