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8375450 
Journal Article 
I-Strain as a Factor in the Chemistry of Ring Compounds 
Brown, HC; Fletcher, RS; Johannesen, RB 
1951 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
73 
1 
212-221 
English 
1. Rates of hydrolysis at 25° in 80% ethanol have been measured for 1-chloro-1-methylcyclopentane, -hexane, -heptane, 1-chloro-1,2-, 1-chloro-1,3- and 1-chloro-1,4-dimethylcyclohexane. cis-and trans-rich fractions of 1,3-dimethylcyclohexanol have been converted to chlorides at 0° and the rates of hydrolysis of the individual products measured. 2. Olefin formation is high for the cyclohexane derivative and is considerably lower for the 5-ring and 7-ring tertiary chlorides. 3. The first order rate constant for the solvolysis is quite small for the cyclohexane derivative and very large for the cyclopentane and cycloheptane derivatives. The introduction of a methyl group in the 2-, 3- and 4-positions of the cyclohexane ring has relatively little effect upon the rate of hydrolysis of the tertiary chloride derived from cyclohexane. 4. It is pointed out that this relative reactivity of the ring systems is also observed in the bimolecular reactions of the cycloalkyl halides. However, in the cycloalkanones the opposite is observed, cyclohexanone being much more reactive than the 5- and 7-membered ring derivatives. 5. The inertness of cyclohexyl halides in displacement reactions is usually attributed to steric hindrance afforded by the puckered ring. This explanation is not in accord with the high reactivity of cyclohexanone toward carbonyl reagents, the high reactivity of cycloheptyl halides in displacement reactions, the marked inertness of 1-chloro-1-methylcyclohexane in solvolytic reactions and the negligible effect of methyl substituents on the rates of such reactions. 6. The peculiar changes in reactivity with ring size are attributed to changes in internal strain accompanying the change in coordination number of a ring atom (I-strain). The I-strain concept permits the chemistry of the small rings (3-, 4-members), the common rings (5-, 6-, 7) and the medium rings (8- to 12-) to be correlated and systematized. © 1951, American Chemical Society. All rights reserved.