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

Abstract

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.

Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

“…The specific rates required for the analyses of the specific rates of solvolysis of 3 , 6 , and 18 are from a recent paper by Reis, Elvas-Leitao, and Martins [38] and those for 11 , 12 , 13 , 14 , 15 , 16 , and 17 solvolyses [35] and for 8 [39] and 19 [40] solvolyses from three papers by Takeuchi and co-workers.…”

Solvent Effects and Steric Course in the Solvolysis of 1,3,3-Trimethyl-2-oxocyclopentyl Mesylate in Comparison with 1,1,3,3-Tetramethyl-2-oxobutyl System

“…Unfortunately, 10OMs is too unstable to prepare: therefore, its rate has to be estimated from that of the chloride, as in the case of 9OMs. From the rate constant of 10Cl in TFE at 25 °C (0.0255 s -1 ) 26 and the mesylate/chloride rate ratio in TFE for 1-adamantyl system 27,28 [0.328/(5.41 × 10 -6 ) = 6.1 × 10 4 ], the 4OMs/10OMs rate ratio is calculated to be 10 -9.6 . Similarly, the 4OMs/10OMs acetolysis rate ratio is evaluated to be 10 -8.…”

Gas-phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

“…In order to remedy this situation, we determined the stability of bridgehead-and bridgehead-like tertiary carbenium ions by ion cyclotron resonance (ICR) techniques. In contrast, the experimental stabilities determined for strained bridgehead cations such as cubyl (12) 3-noradamantyl (13), 1-norbornyl (14) and others (1and 4-homocubyl) were essentially meaningless and could not be correlated with anything (J.-L. M. Abboud, E. W. Della, P. Müller, R. Notario and J.-C. Rossier, unpublished work). 3 The correlation was, however, only partially satisfactory, because the value for the 1-norbornyl derivative was found significantly below the correlation line, while simple acyclic and monocyclic derivatives such as tertbutyl solvolyzed much faster than expected on the grounds of the stability of the respective carbenium ions, and were, therefore, found above the correlation line.…”