Structural modification and solvent interactions in solvolytic reactions of open-chain compounds

The Grunwald-Winstein type analyses with respect to Ycl scale on the specific rates of solvolysis of extremely crowded tertiary alkyl chlorides having a neopentyl or a (1-adamanty1)methyl group at the reaction center show that they behave as k, substrates. The neopentyl group is more effective in backside shielding than a tertiary butyl group. There are now many unprecedented examples that show downward dispersions of aqueous ethanol and aqueous acetone data points relative to fluorinated solvents in the Grunwald-Winstein type relations. The principal cause for such behavior is attributed to diminished rates in water relative to those in nonaqueous solvents. In the solvolyses of (t-BuCHz)Et2CCl and (t-BuCH2)2MeCCl (9), the deviated aqueous ethanol data exhibit a downward convex, enhancing the downward deviations. Secondary mesylates, (t-BuCH2)2CHOMs and (t-BuCH2)( 1 AdCH2)CHOMs, and even l-bromo-3,5,7-triisopropyladamantane behave similarly to congested tertiary open-chain alkyl chlorides. In the solvolysis of 9 in aqueous ethanol, the product selectivity with respect to ethanol is considerably increased compared with the case of tert-butyl chloride. Steric and hydrophobic perturbation to solvation in the ground state and intermediate would provide a reasonable explanation.