Diazomethane and diazirine

The energy difference between diazirine and diazomethane, interesting from the point of view of their isomerism, came from MS measurements (63JCP(39)3534). The appearance potentials of the CH2 ion, common to both compounds, yielded a difference in heats of formation of 125kJmor A strong peak in the mass spectrum of 3-chloro-3-methyl-diazirine (50) with relative mass 55 was ascribed to the methyldiazirinium ion (51). 

N. Yamamoto, F. Bernardi, A. Bottoni, M. Olivucci, M. A. Robb, and S. Wilsey,J. Am. Cbem. Soc., 116, 2064 (1994), and references cited therein. Mechanism of Carbene Formation from the Excited States of Diazirine and Diazomethane An MC-SCF Study. 

Figure 1 Relative thermodynamic stability of substituted diazirines and diazomethanes (kcal mol).

Theoretical predictions on photochemical and thermal isomerization of diazirines may explain numerous experimental values. Due to low and reversible relative stability of diazirines and diazomethanes, which depend on substituents (Figures 1 and 2), the spontaneous <63TL1405>, photochemical <64JA292>, or thermal <77JCS(P2)1214> isomerization of diazirines into diazoalkane has been observed, as well as reversible isomerization of diazocarbonyl compounds and corresponding diazirines. Interconversions of diazirines and diazo compounds have been considered in detail [Pg.352]

Yamamoto N, Bemardi F, Bottoni A, Ohvucci M, Robb M, Wilsey S. Mechanism of carbene formation from the excited-states of diazirine and diazomethane — an MC-SCF study. J Am Chem Soc. 1994 116 2064-2074. 

The photoisomerization of diazirines to diazomethanes has been observed in other liquid-phase photolyses and will be discussed later, but its occmTence in the case of diazirine itself presents quite unique problems. On the basis of the appearance potentials of diazomethane and diazirine, the heats of formation of these compounds have been esti-... 

Two bonds formed by a N atom having one or two lone pairs would be expected to be angular with bond angles of 120 (one lone pair, sp bonds) or 109 (two lone pairs, sp bonds). (Molecules such as diazirine (cyclic diazomethane) and perfluorodiazirine are special cases like cyclopropane or ethylene oxide.) If the... 

Arenas, J. F., Lopez Tocon, I., Otero, J. C., Soto, J., Carbene Formation in Its Lower Singlet State from Photoexcited 3H Diazirine or Diazomethane. A Combined CASPT2 and Ah Initio Direct Dynamics Trajectory Study, J. Am. Chem. Soc. 2002, 124, 1728 1735. 

It is, therefore, not surprising that all these isomers of diazomethane have attracted the attention of physical chemists interested in the experimental determination of heats of formation and in theoretical calculations of thermodynamic stabilities. From mass spectra and appearence potentials, Paulett and Ettinger (1963a, 1963b) estimated the heat of formation to be 331 kJ mol for diazirine and 206 kJ mol for diazomethane. In other words, diazirine is thermally less stable than diazomethane by 125 kJ mol Shortly after these investigations. Bell (1964) suggested that the heats of formation should be calculated using a different set of assumptions, which resulted in lower absolute values, but still with the same difference between A//f for diazomethane and diazirine. ... 

The formation of diazirine from diazomethane may, however, also proceed via complete dissociation to CH2 and N2. So far as we are aware, this question has not been verified experimentally. 

Computational studies have compared substituent effects on the stability of ketenes, allenes, diazomethanes, diazirines, and cyclopropenes. Ketenes belong to the first generation of reactive intermediates along with carbocations, carbanions, radicals, and carbenes, and are intensively studied members of the cumulene family, with many useful synthetic applications. Ketenes were first recognized in 1905, when diphenylketene, a stable and isolable example, was obtained from the dehalogenation of the a-bromodiphenylacetyl bromide (Scheme 7.37). The most characteristic reaction of ketene is cycloaddition, as in the formation of p-laclams. 

Carbene Formation in Its Lower Singlet State from Photoexcited 3H-Diazirine or Diazomethane. A Combined CASPT2 and Ab Initio Direct Dynamics Trajectory Study. 

FIGURE 92.1 Schematic of the ground, first excited singlet, and second excited singlet surfaces of diazirine. DZ = diazirine, DM = diazomethane, TS = transition state. Cl = conical intersection, and VL = vibrational leakage. 

It is interesting to note that the existence of an isomer of diazomethane with a diazirine structure was never discussed, so the report on its synthesis 61TL612) simultaneously started and ended the discussion on its existence. 

Even more recent calculations using STO-3G and 6-31G basis sets could not safely predict diazomethane as the more stable compound in comparison with diazirine, although there is an experimental energy difference of 125 kJ moP 79JST(52)275). 

Formation of diazomethane from diazirine was also observed in a solid nitrogen matrix on irradiation (64JCP(41)3504). Labeling experiments demonstrated that elimination and uptake of nitrogen occurred. 

Examine acyclic (diazomethane) and cyclic (diazirine) structures of molecular formula CH2N2. Which is the more stable Is the less stable structure an energy minimum Examine vibrational frequencies to tell. 

For the preparation of the parent substance, cyclic diazomethane (67), formaldehyde, chloramine, and ammonia were reacted. Diaziri-dine formation was successful in about 20% yield the diaziridine condensed with further formaldehyde to high molecular weight products the diaziridine detected by its oxidizing power was nonvolatile. Oxidation with dichromate in dilute sulfuric acid led to gaseous diazirine (67) [Eq. (56)]. It was only investigated in solution. 

Preliminary investigations on the formation of carbenes from diazirines have already been made available. Frey and Stevens recently reported the photolysis of cyclic diazomethane. Cyclic diazomethane was irradiated in the gaseous phase with light of wavelength... 

Diazirine is a cyclic isomer of diazomethane. According to the organometallic literature, scission of both C-N and N-N bonds can occur when diazirines interact with metal complexes. The formation of carbene ligands arises from selective cleavage of the C-N bond, whereas selective N-N bond scission results in the formation... 

Confirmation was provided by the observation that the species produced by the photolysis of two different carbene sources (88 and 89) in acetonitrile and by photolysis of the azirine 92 all had the same strong absorption band at 390 nm and all reacted with acrylonitrile at the same rate (fc=4.6 x 10 Af s" ). Rate constants were also measured for its reaction with a range of substituted alkenes, methanol and ferf-butanol. Laser flash photolysis work on the photolysis of 9-diazothioxan-threne in acetonitrile also produced a new band attributed the nitrile ylide 87 (47). The first alkyl-substituted example, acetonitrilio methylide (95), was produced in a similar way by the photolysis of diazomethane or diazirine in acetonitrile (20,21). This species showed a strong absorption at 280 nm and was trapped with a variety of electron-deficient olefinic and acetylenic dipolarophiles to give the expected cycloadducts (e.g., 96 and 97) in high yields. When diazomethane was used as the precursor, the reaction was carried out at —40 °C to minimize the rate of its cycloaddition to the dipolarophile. In the reactions with unsymmetrical dipolarophiles such as acrylonitrile, methyl acrylate, or methyl propiolate, the ratio of regioisomers was found to be 1 1. 

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