The Influence of Carbon-Carbon Multiple Bonds on the Solvolyses of Tertiary Alkyl Halides: a Grunwald-Winstein Analysis

Abstract

Abstract:The influence of carbon-carbon multiple bonds on the solvolyses of 3-chloro-3-methylbutyne (1), 2-chloro-2-phenylpropane (2), 2-bromo-2-methyl-1-phenylpropane (3), 4-chloro-4-methyl-2-pentyne (4) and 2-chloro-2-methylbutane (5) is critically evaluated through the extended Grunwald-Winstein equation. Substrates 1, 3 and 5 lead to correlations with unexpected negative sensitivity, h, to changes in the aromatic ring parameter, I. It is claimed that I is not a pure parameter, reflecting also some solvent nucleophilicity, N OTs , character. In substrates 2 and 4 the possibility of rearside solvation is reduced due to steric hindrance and/or cation stabilization and the best found correlations involve only the solvent ionizing power, Y, and I.

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.…”

“…Except for compound 12B , data from a paper by Martins and coworkers [38], the specific rate values are from a publication by Liu and coworkers [42]. They carried out the study using a series of bromides with gradually increasing steric hindrance to nucleophilic attack at the α-carbon.…”

“…As regards the solvent nucleophilicity scale, Takeuchi and coworkers [40] have used the N T scale but Liu and coworkers [33, 42] and Martins and coworkers [38] have both used the N OTs values. The need to arrive at an approximation for the dependence on solvent ionizing power, so as to subtract the mY OTs value from log ( k / k o ) in arriving at N OTs values based on methyl p-toluenesulfonate has been extensively discussed [2, 19] and it has been demonstrated that the 0.3 value employed should have been about 0.55, supported by the observation that revised N’ OTs values are in excellent agreement with N T values [2, 19].…”

On the Importance of the Aromatic Ring Parameter in Studies of the Solvolyses of Cinnamyl and Cinnamoyl Halides

“…Recently, Martins and coworkers [18] applied equation 4 to the specific rates of solvolysis of five moderately-hindered tertiary alkyl halides (substrates mostly with the absence of π-electrons) and found the sensitivities ( h ) to changes in the aromatic-ring parameter ( I ) were sometimes positive and sometimes negative. They suggested that the negative h values arose because I was not a pure parameter and proposed that it included a solvent nucleophilicity component [18].…”

“…They suggested that the negative h values arose because I was not a pure parameter and proposed that it included a solvent nucleophilicity component [18]. After a thorough analysis of the available specific rates of solvolyses of 30 highly-hindered tertiary alkyl derivatives, we concluded in a recent review [19] that it appears that the apparent utility of the hI term for substrates not having appropriately placed π-electrons is an artifact resulting from moderate multicollinearity that is present between the I values and a linear combination of N T and Y X values.…”