The effect of electron flow through a complete circuit on transition state acid dissociation constants is used to explain the remarkable catalysis observed in a redox reaction, the formation of compound I from native peroxidase. The explanation for the huge shift in the dissociation constant of a distal histidine residue, in going from the resting enzyme to the transition state, is a complete electron circuit through many amino acid residues and hydrogen bonds which prevents the development of localized charge. The key feature is electron flow through the circuit at the instant that proton transfer is occurring in the opposite direction. Electron flow occurs in one direction for attainment of the transition state and in the opposite direction for product formation.

The reactions of active nitrogen with methyl, ethyl, vinyl, propyl, and isopropyl chlorides yielded hydrogen cyanide and hydrogen chloride as the maill products. Small amounts of cyanogen and a polymer were formed from all the halides, and all except methyl chloride also yielded small amounts of C? and C3hydrocarbons. The observed changes in amoulits of products recovered with different reactant flow rates were characteristic of a fast reaction in which complete consumption of either reactant occurs when the other is present in excess. Mechanisms for the reactions are suggested on the basis that relatively longlived complexes are formed in the initial attack of a nitrogen atom on the alkyl chloride. INTRODUCTIONA number of reactions of active nitrogen, produced in a condensed electrical discharge, have been studied in this laboratory. Emphasis has been placed largely, though not exclusively, on the reactions with hydrocarbons (2, 3, 9, 11, 13, 14, 17, 18, 19). Hydrogen cyanide is the main nitrogen-containing product of these reactions, which implies that the reactions with saturated hydrocarbons involve direct attack a t a completely shielded carbon atom. They are much faster than would be expected from the principle of least motion enunciated by Rice and Teller (15).In an attempt to elucidate further the mechanism of the reactions, it appeared desirable to investigate the effect of a chlorine substituent on the reactivity. Accordingly, the reactions of active nitrogen with methyl, ethyl, vinyl, propyl, and isopropyl chlorides have been studied. EXPERIMENTALThe reactions were studied with conventional fast-flow techniques (11). Active nitrogen was produced by a condensed discharge and mixed with the halides in a reaction vessel that was sufficiently far from the discharge tube to prevent back diffusion into the discharge. The flow and activation of the nitrogen were kept constant in experiments with a given halide and the effects of change in flow rate of the halide determined. The reaction vessel could be surrounded by a furnace to study the effect of temperature. Condensable products were trapped with the usual arrangement of liquid air traps, and were analyzed by low temperature fractionation (12) and with a mass ~pectrometer.~ The hydrogen cyanide, cyanogen, and hydrogen chloride produced in the reactions were estimated by titration (16, 20). The hydrogen produced in the reaction with methyl chloride was determined mass spectrometrically on samples of the gas issuing from the vacuum pump.'Manz~script

The second-order rate constant for the oxidation of NADH by methylene blue at pH 9.0 and 25°C under aerobic conditions is 4.21 M-' s-l.0