Effect of cyano group substitution on metathetical reactions. IV. Substituent effects on the rates of cyanomethyl radical reaction with haloalkanes

✍ Scribed by Y. Gonen (Geliebter); A. Horowitz; L. A. Rajbenbach

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 604 KB
• Volume: 13
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550130302

✦ Synopsis

Gamma radiation-induced free radical chain reactions in liquid mixtures of BrCHpCN, cyclohexane (RH), and haloalkanes (XCC13) were studied. The kinetics of hydrogen and chlorine atom abstraction from CHC13, CH3CC13, CHzClCC13, CHClzCC13, CF3CC13, CpC16, CC13CN, and ccl4 by CHzCN radicals were investigated by a competitive method. The reactions investigated were

Rate constant ratios k3/kz, k5/kGr k7/kpr and ks/kV were determined a t 180°C. In the CCL-RH-BrCHzCN system k3/kz was determined in the temperature range of 100-180°C, yielding log k2/k3 = -0.11 f 0.2 -(3.34 f 0.39/0) where 0 = 2.3RT in kcal/mol. The value Ez -E3 was combined with existing data on E3 to yield Ep(CCl4) = 17.57 kcal/mol. The reactivity trend of CHzCN is compared with that of R radicals. I t is shown that in spite of a difference of about four orders of magnitude in kcl values, the reactive cyclohexyl radical is somewhat more selective than CHzCN. It is proposed that the relative reactivities log[kz(XCCl3)/k2(CH3CCl:3)] can be correlated in terms of a dual-parameter Taft equation which takes into account both resonance and inductive substituent effects.