Photoisomerization of Azomethane

Abstract

COMMUNICATIONS TO THE EDITOR745 I For the ethyl radical, B has a value of 58.5 gauss.' Solution of the equations, aaxia1.H = Bp COS2 eaxial, Uequat-H = Bp COS2 eequat, and Oequat-H = Baxial-H f 120' (tetrahedral a-carbon atom) gives the results listed in Table I. 6 It is interesting that the value of Oaxial for the a-hydrogens of the 4-t-butylcyclohexane-1,2-dione radical-anion is the same as found for cyclohexene by n . m .~-.~ Our results demonstrate the application of e.s.r. to conformational analysis of nonrigid systems and suggest the use of e.s.r. for structural determinations of rigid ketonic systems, such as the steroidal ketones. Work in this area is in progress. (5) R. W. Fessenden and R . H . Schuler, J . Chem. P h y s . , 89, 2147 (1963). These authors determined Qp (CHa). Since c 0 s~4 5~ (free rotation) is * / n , B is twice their value of Qp (CHd (6) Two values of Bp and two values of 0 (except when cos2 Oequat.H = 0) are obtained (7) G. V . Smith and H . Kriloff, J . A m . Chem Soc., 86, 2016 (1963) These authors use a dihedral angle for axial hydrogens equivalent to 90' (8) (a) Alfred P . Sloan Foundation Fellow, 1959-1963; (b) National Unrealistic solutions ( B p > 58.5/2) have not been listed e. . Photoisomerization of Azomethane Sir :Although cis-trans isomerization is well-established for aromatic azo compounds,1,2 it has not been observed in the aliphatic series. We wish to report experiments in which the photochemical cis-trans isomerization of azomethane and the isolation of pure cis-azomethane have been achieved.Azomethane (I) ~ which exists in the trans configurat i~n ,~-~ photolyzes readily in the gas phase, yielding nitrogen and two methyl radicals. In agreement with previous work,6 the quantum yield ( 4~~) for the photolytic decomposition of gaseous azomethane (I) by 365mp light was found to be 1.0 f 0.1. In marked contrast, the quantum yield decreases dramatically when azomethane is irradiated in solution. Thus, for carefully degassed 5 X M solutions in isooctane, ethanol, N,N-dimethylformamide, and water a t 25", the quantum yields, determined by nitrogen formation, (1) G. Zimmerman, I,. Chow, and U. Paik, J. A m Chem. Soc.. 80, 3528 (1958); E. Fischer, ibid., 81, 3249 (1960).(2) c i s and trans isomers of difluorodiazine (NzFd are known: C. B.were, respectively, 0.17 f 0.01, 0.07 f 0.01, 0.05 f 0.01, and 0.01 f 0.01. In addition, fluorescence was not detected in any of these solutions. However, chemical transformation does attend irradiation of azomethane in degassed solution and can be observed by ultraviolet absorption and by proton magnetic resonance spectroscopy. A solution of azomethane (I, to lo-' M ) in degassed DzO shows a single sharp resonance lying a t 6 $0.984 ~. p . m . ,~ and is indefinitely stable in the dark a t room temperature. Upon irradiation of the solution a t room temperature, a new sharp singlet (11) appears 0.10 p.p.m. to high field from the resonance of I . By following the ratio of the height of the new resonance (11) to that of I as a function of irradi...

Quantum and semiclassical dynamical studies of nonadiabatic processes in solution: achievements and perspectives

“…25,26 QM(GVB-CAS)/MM dynamics on trans-azomethane revealed that the decay lifetimes, associated with the torsion around the central double bond, are mainly influenced by mechanical restrictions from interactions with the solvent, and do not depend on the polarity, with similar decay times in polar and non-polar solvents. 161 Furthermore, these simulations also confirmed the absence of dissociation processes in solution, in agreement with experimental results 171 and other dynamic studies. 172 Surface hopping SA-CASSCF(10,8)/MM simulations have been performed on 9H-hypoxanthine and its methylated derivative (9M-hypoxanthine) in the gas phase and water.…”

cis-Azoxyalkanes. IV. Preparation and nuclear magnetic resonance spectra

“…Configurational isomers of acyclic analogs azoisobutane (ArcH,(transcis) = 0.33 ppm (CH30D))34 and azoisopropane (15) ( A~~~~( t r a n s -c i s ) = 0.14 ppm, ArcH(trans-cis) = 0.49 ppm (CCL))15 behave likewise while the parent, azomethane (ArcH,(trans-cis) = -0.10 ppm (DzO)), 35 falls outside the pattern. Configurational isomers of acyclic analogs azoisobutane (ArcH,(transcis) = 0.33 ppm (CH30D))34 and azoisopropane (15) ( A~~~~( t r a n s -c i s ) = 0.14 ppm, ArcH(trans-cis) = 0.49 ppm (CCL))15 behave likewise while the parent, azomethane (ArcH,(trans-cis) = -0.10 ppm (DzO)), 35 falls outside the pattern.…”

Transformations of 4,9-dimethyl-2,3,7,8-tetra-azatetracyclo[7.3.1.0.4,1206,10]trideca-1,6-diene, a bishydrazone having two bridgehead double bonds

“…spectra and comparison with the spectra of some model compounds. The pyrazole (7) is characterised by the resonance of the 5-methyl at r 7.48, shielded by the anisotropic effect of the carbonyl group relative to the resonance of the 3-methyl at r 7.78. To facilitate comparisons and avoid complications of possible changes in preferred conformations a further model compound, the bicyclic pyrazole ( 8), was prepared by reaction of hydrazine with 2-acetylcyclohexanone and subsequent acetylation with acetic anhydride in pyridine.…”

“…105-106 "C (lit., m.p. 106 oC).8 Acetylation by Method A afforded a yellow oil, which on distillation gave as a colourless oil 1-acetyl-3,5dimethyl-lH-pyrazole (7) 5,6, .-A solution of 2-acetylcyclohexanone (1 .O g) and hydrazine hydrate (0.4 ml) in ethanol (20 ml) was stirred at room temperature for 30 min. Concentration under reduced pressure afforded a yellow oil (1.1 g) which was acetylated by Method A at room temperature for 16 h. Concentration under reduced pressure afforded a yellow oil (1.25 g) which was purified by bulb-to-bulb distillation (100 "Cl0.1 mmHg) to give initially a colourless oil which slowly solidified.…”