Nitrogen inversion temperature

Diaziridines also show slow nitrogen inversion, and carbon-substituted compounds can be resolved into enantiomers, which typically racemize slowly at room temperature (when Af-substituted with alkyl and/or hydrogen). For example, l-methyl-3-benzyl-3-methyl-diaziridine in tetrachloroethylene showed a half-life at 70 °C of 431 min (69AG(E)212). Preparative resolution has been done both by classical methods, using chiral partners in salts (77DOK(232)108l), and by chromatography on triacetyl cellulose (Section 5.08.2.3.1). 

Figure 3.7(a) compares the experimental inversion curve for nitrogen gas with the van der Waals prediction. Considering the approximations involved, it is not surprising that the quantitative prediction of the van der Waals equation is not very good. Equation (3.91) is quadratic in T and hence, predicts two values for the inversion temperature, which is in qualitative agreement with the experimental observation.1... 

Figure 5.8. Locus of Joule Thomson inversion temperatures for nitrogen. Data from J. R. Roebuck and H. Osterberg, Phys. Rev. 48, 450 (1935).

Rate process with activation energies between 6 and 25 kcal mol-1 can be studied conveniently by the NMR method. Line shape theories have been well reviewed.103 In most cases a single rate constant k is estimated at the coalescence temperature, and AG is obtained from the Eyring equation. For exchange between two unequally populated sites, AG for the forward and reverse reactions are different. This is an important point to be considered in the case of nitrogen inversion phenomena. 

If ring inversions are assumed to be of high energy, then at temperatures where ring inversions and passing nitrogen inversions are slow but... 

Variable temperature 13C NMR spectroscopy has shown that the 1,2,3,4,5,6-hexamethyl-hexahydro-l,2,4,5-tetrazine (57) is the trans isomer with the two C-methyl groups equatorial and the N-methyl groups symmetrically diaxial and diequatorial. The observed dynamic 13C NMR effects are consistent with (57a) and (57b) as the major conformation and probably (57c) as the minor one. The first coalescence represents the freezing out of (57c) while the (57a) (57b) interconversion remains fast. The nitrogen inversion barrier was found to be 32.2 kJ moF1 <79JCS(P2)98l). The He(I) photoelectron spectrum of (57) confirmed the NMR data (80JCS(P2)9l). 

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