Effect of Negative Groups on Reactivity

Abstract

REGENT experimental and theoretical studies of bond strength¹ have shown that our forecast², according to which in the series of gas reactions Na + XR = NaX + R (X = halogen, R = R₁, R₂ …) the reactivity is inversely related to the bond strength C–X, holds true for hydrocarbon radicals R₁, R₂ … containing no negative groups. But the great acceleration caused by the presence of such negative groups (X₁, X₂ …) in reactions of the type Na + XRX₁ = NaX + RX₁ is as yet unexplained. The presence of these groups is not usually considered to weaken the bond strength C–X. In fact, it has been suggested by Pauling that, when X₁, X₂ … are halogen atoms attached to the same carbon as X, the strength of all the halogen bonds is rather increased than decreased by resonance³. Moreover, observations on the bond energy of acetyl iodide¹ failed to reveal any such weakening of the carbon halogen bond by the negative substituent (= O), which could explain that acetyl chloride reacts much faster with sodium vapour than does C₂H₅Cl⁴.