Structural effects of the Grunwald–Winstein correlations in the solvolysis of some simple tertiary alkyl chlorides

✍ Scribed by Kenichi Takeuchi; Yasushi Ohga; Takushiro Ushino; Masaaki Takasuka

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 104 KB
• Volume: 10
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199710)10:10<717::aid-poc941>3.0.co;2-y

✦ Synopsis

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/k 0 )=mY Cl + c and log(k/k 0 )=lN T + mY Cl + 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.