A theoretical study on the bimolecular hydrogen exchange aminonitrene → trans-diimide. Comparison with formaldehyde photochemistry

Abstract

. Can. J . Chem. 59, 3044 (1981).Ah initio calculations on the rearrangement aminonitrene -, trans-diimide are reported. It is shown that a bimolecular hydrogen exchange is much easier than a unimolecular 1,2 hydrogen shift: the reactions have activation energies of 4 and 94kcal/mol, respectively. The hydrogen exchange starts from dimers which have a fairly large stabilization energy. Infrared and Raman frequencies of these dimers are calculated in order to facilitate experimental studies. Some striking similarities are indicated between diimide chemistry and the photochemistry of formaldehyde. It is shown that results from one field are transferable to the other one. On indique des similarites frappantes entre la chimie des diimides et la photochimie de la formaldehyde. On montre que ces resultats sont transferables d'un champ a I'autre. On suggere de nouvelles experiences a partir de ces donnees.[Traduit par le journal]

The preparation, properties and reactions of diimide

“…This reaction would the endothermic only by the difference in heats of formation of the two isomers, and could have a very low barrier; a similar process has been suggested for the isomerization of aminonitrene [97]. Kinetic evidence does not support this mechanism, nor a surface isoraerization, but there is enough uncertainty in the experiments that these possibilities cannot be ruled out [25].…”

“…The isomerization of aminonitrene to diimide has been considered theoretically in several articles [43,45,57,58,97]. High barriers are found (SO to 75 kcal mol -I) and aminonitrene appears to be at least 25 kcal mol -I less stable than trans-diimide.…”

Studies on the mechanism of the hydrazine reduction reaction: Applications to selected monoethylenic, diethylenic and triethylenic fatty acids ofcis configurations

“…In general, the oxidaton step to produce [4] could occur anywhere in the solution, and most molecules of [4] would simply disproportionate or decompose without effecting any reduction--a large excess of hydrazine is used and there is no evidence that the reduction reaction is efficient in terms of hydrazine consumption. However, ifa molecule of [4] is produced in proximity to a double bond, the two would interact in the normal way that 7r clouds interact with electrophilic species to form a loose complex [5], which could be deprotonated to form cis-diimide [2], in very close proximity to the alkene 7r cloud. Concerted, stereoselective transfer of two hydrogen atoms to the alkene would then be very rapid and exothermic, and would undoubtedly occur before the molecule of [2] could diffuse away into the reaction medium.…”

“…The whole process is outlined in Scheme 2. The equilibrium constant for the formation of [5] will depend on the steric environment of the double bond, and the proximity of a carboxylate anion would improve the entropy of the reaction, leading to higher reaction rates.…”

“…The use of hydrazine for the reduction of ethylenic (olefinic) bonds has been known for almost eighty years and is believed to involve the intermediacy of diimide (HN=NH, [1 ]), a reactive species that first excited considerable attention some twenty years ago (1,2). A range of papers describing calculations on (3)(4)(5)(6)(7), or properties of (8)(9)(10), diimide is evidence of a continuing interest in unravelling the chemistry of this species. The hydrazine reduction reaction has found favor for reductions of unsaturated fatty acids (11)(12)(13) because no apparent cistrans isomerism or ethylenic bond positional shifts occur, in strong contrast to the results from the use of catalytic hydrogenation (14).…”