The influence of the nitro-group upon side-chain reactivity. Part VII. Substitution and elimination reactions in 2-chloropropene systems

Abstract

Kinetics studies of the action of sodium methoxide in methanol and of sodium ethoxide in ethanol on the chloropropenes trans-p-NO₂·C₆H₄·CHCClMe (I), its structural isomer p-NO₂·C₆H₄·CH₂·CClCH₂(II), and trans-2,4-(NO₂)₂C₆H₃·CHCClMe (III) show that (i) whereas one nitro-group in the ring (I) allows for S_N2 etherification (15–17 times faster with ethoxide than with methoxide), two nitro-groups III) favour the β-elimination to the acetylene (50–55 times faster with ethoxide than with methoxide); (ii) with methoxide in methanol at 30° the β-elimination reaction of (III) is 1200 times faster than the S_N2 etherification of (I); the entropy of activation of the elimination reaction is highly positive and suggests its occurrence by the irreversible E1cB mechanism; (iii) at 35°, the initial rate of liberation of chloride from (II) by methoxide in methanol is 440 times that from (I). The significance of these results is discussed.