27396-17-4Relevant academic research and scientific papers
Thermolysis of tert-butyl phenylperacetates: Delicate control of the rates through contributions from translational and rotational entropy
Kim,Baek,Tuchkin,Go
, p. 4006 - 4011 (2007/10/03)
The first-order rate constants (ky) at several temperatures in CDCl3 were measured for thermal decompositions of YC6H4CH2CO3C(CH3) 3 with Y being p-OCH3, p-OPh, p-CH3, p-Ph, p-H, p-Cl, m-Cl, and p-NO2. The relative rates (ky/kH) exhibit excellent ρ+/σ+ Hammett correlations with ρ+ a polar TS. Activation parameters (ΔH?Y and ΔS?Y) and their differential terms (ΔΔH?Y-H and ΔΔS?Y-H) were obtained from the Eyring plot. Differential activation terms (ΔΔH?Y-H and ΔΔS?Y-H) disclose an isokinetic relation with p-CH3, p-Ph, p-H, p-Cl, and m-Cl (isokinetic temp, 230 K). However, p-OCH3, and p-OPh show negative deviations, and a positive deviation occurs with p-NO2. Plot of ΔΔH?Y-H vs σ+ exhibits a good linear relation (r = 0.95) with a slope (α1 = -3.34). A better linear correlation (r = 0.97) and steeper slope (α2 = -5.22) were observed for TΔΔS?Y-H vs σ+. Negatively larger slope (α2 = -5.22) may point to entropy control of rates. Differential activation parameters (ΔΔHS?Y-H and ΔΔS?Y-H) reflect variations of activation process. Differential activation entropies (ΔΔS?Y-H) are discussed in terms of contributions of translational and rotational entropies. Similar deviation behaviors of p-OCH3, p-OPh, and p-NO2 were again observed for the both plots. p-NO2 can strongly destabilize the cationic site of the polar TS but serves an eminent spin delocalizer for the homolytic TS.
