AROMATIC SUBSTITUTION: PART VIII. SOME ASPECTS OF THE MECHANISM OF THE TSCHITSCHIBABIN REACTION

1965 ◽  
Vol 43 (4) ◽  
pp. 725-731 ◽  
Author(s):  
R. A. Abramovitch ◽  
F. Helmer ◽  
J. G. Saha
Keyword(s):  
Molecular Orbital ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Aromatic Substitution ◽  
Direct Amination ◽  
Detailed Mechanism ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Rule Out

The mechanism of the direct amination of pyridines is discussed in terms of both addition–elimination and elimination–addition pathways. The absence of deuterium kinetic isotope effects as well as the orientations observed in such reactions rule out the intervention of 2,3- or 2,6-dehydropyridines. The effect of a 3-methyl group upon the reactivities towards the amide ion of the various nuclear positions in pyridine has been determined. Predictions based on molecular orbital (m.o.) calculations are discussed in terms of the detailed mechanism of this reaction and of the orientations observed.

Kinetics and mechanism of oxidation of N,N′-dimethyl-9,9′-biacridanyl by some π acceptors and a one-electron oxidant

1985 ◽  
Vol 63 (2) ◽  
pp. 445-451 ◽  
Author(s):  
Allan K. Colter ◽  
Charles C. Lai ◽  
A. Gregg Parsons ◽  
N. Bruce Ramsey ◽  
Gunzi Saito
Keyword(s):  
Electron Transfer ◽  
Reduction Potential ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Kinetic Isotope Effects ◽  
Spin Trapping ◽  
Single Electron Transfer ◽  
Kinetic Isotope ◽  
The One ◽  
Rule Out

Oxidation of N,N′-dimethyl-9,9′-biacridanyl (DD) has been investigated as a model for single electron transfer (SET)-initiated oxidation of NADH coenzyme models such as N-methylacridan (DH). Oxidants investigated cover a 1010-fold range of reactivity in acetonitrile and include the π acceptors 1,4-benzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCIBQ), p-chloranil (CA), 2,3-dicyanobenzoquinone (DCBQ), 2,3-dicyano-1,4-naphthoquinone (DCNQ), 2,3-dicyano-5-nitro-1,4-naphthoquinone (DCNNQ), 9-dicyanomethylene-2,4,7-trinitrofluorene (DCMTNF), 9-dicyanomethylene-2,4,5,7-tetranitrofluorene (DCMTENF), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE), and the one-electron oxidant tris(2,2′-bipyridyl)cobalt(III), [Formula: see text] The oxidation product is, in every case, N-methylacridinium ion (D+). A mechanism involving a rate-determining electron transfer with simultaneous fragmentation to D+ and N-methyl-9-acridanyl radical (D•) is proposed. This mechanism is supported by the observed dependence of the rate on oxidant reduction potential, by spin-trapping experiments, by kinetic isotope effects in oxidation of 9,9′-dideuterio-DD, and by substituent effects in oxidation of 2,2′- and 3,3′-dimethoxy-DD. The rate of oxidation of DD relative to that of DH is 3.4 × 102 with [Formula: see text] and with the π acceptors varies from ea. 0.3 (BQ) to 8.1 × 104 (DCMTENF). The results rule out a SET-initiated mechanism for oxidation of DH by all of the oxidants studied except TCNQ and DCMTENF.

SECONDARY KINETIC ISOTOPE EFFECTS IN BIMOLECULAR NUCLEOPHILIC SUBSTITUTIONS: II. α-DEUTERIUM EFFECTS IN MENSCHUTKIN REACTIONS OF METHYL IODIDE

1965 ◽  
Vol 43 (1) ◽  
pp. 40-46 ◽  
Author(s):  
K. T. Leffek ◽  
J. W. MacLean
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Systematic Change ◽  
Tertiary Amines ◽  
Nucleophilic Substitutions ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Deuterium Substitution ◽  
Different Temperatures ◽  
Rate Ratios

Secondary deuterium isotope effects have been measured for the reactions between methyl and methyl-d3 iodides and a series of tertiary amines in benzene solvent. Deuterium substitution increased the rate of each reaction but the rate ratios (kH/kD) show no systematic change with variation in the structure of the amine. The isotope effect for the reaction with 2-picoline was measured at different temperatures over a range of 40 deg and shows no change. These isotope effects may be rationalized as internal rotational effects of the methyl group or as solvation effects.

Competitive photochlorination and kinetic isotope effects for hydrogen/deuterium abstraction from the methyl group in C2H6, C2D6, CH3CHCl2, CD3CHCl2, CH3CCl3, and CD3CCl3

1985 ◽  
Vol 63 (5) ◽  
pp. 1093-1099 ◽  
Author(s):  
E. Tschuikow-Roux ◽  
Jan Niedzielski ◽  
F. Faraji
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Arrhenius Law ◽  
Chloromethyl Group ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Hydrogen Deuterium

The abstraction of hydrogen and deuterium from ethane, 1,1-dichloroethane, 1,1,1-trichloroethane, and some of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigated in the temperature range 7–95 °C using methane as competitor. Rate constants and their temperature coefficients are reported for the following reactions:[Formula: see text]An Arrhenius law temperature dependence was observed in all cases. Mixed primary and α-secondary kinetic isotope effects are k1/k2 = 2.79 ± 0.27, k4/k6 = 4.13 ± 0.32, k7/k8 = 1.46 ± 0.12 at 298 K and decrease to k1/k2 = 2.53 ± 0.22, k4/k6 = 4.06 ± 0.28, k7/k8 = 1.45 ± 0.09 at 370 K, showing a "normal" temperature dependence. The kinetic isotope effect for H/D abstraction from the methyl group decreases with increasing number of chlorine substituents in the adjacent chloromethyl group. The β-secondary isotope effect, k3/k5, is close to unity and shows a slight inverse temperature dependence.

Sign in / Sign up

Export Citation Format

Share Document