Nitrogen rate determining steps

The mechanism of the synthesis reaction remains unclear. Both a molecular mechanism and an atomic mechanism have been proposed. Strong support has been gathered for the atomic mechanism through measurements of adsorbed nitrogen atom concentrations on the surface of model working catalysts where dissociative N2 chemisorption is the rate-determining step (17). The likely mechanism, where (ad) indicates surface-adsorbed species, is as follows ... 

One may conclude that the rate-determining step of the renaturation is at least partly influenced by the cis-trans isomerization of the peptide bond the secondary nitrogen atom of which arises from proline. Otherwise, only the entropy-controlled slow nuclea-tion should be observed kinetically. The covalent bridging through Lys-Lys, therefore, gives rise not only to thermodynamic stabilization of the triple helix but also to kinetic properties which have hitherto been observed in the case of type III procollagen146) and its aminoterminal fragment Col 1-3144). 

This observation is consistent with the assumptions of the authors predicting microwave effects when the polarity is enhanced in a dipolar TS. The kinetic rate-determining step consists of an intramolecular attack of the nitrogen lone pair on the carbon atom of the carbonyl moiety (Scheme 3.15). 

Aryl sulfinyl azides, ArS(0)N3, can be prepared at low temperature by reaction of sulfinyl chloride ArS(0)Cl with sodium azide (Maricich and Hoffman, 1974). On warming to 0° they decompose with evolution of nitrogen, their decomposition exhibiting clean first-order kinetics ( = 3 x 10-4 s-1 for PhS(0)N3 in acetonitrile at 0°). The rate-determining step of the decomposition is loss of nitrogen from the sulfinyl azide to form the sulfinyl nitrene ArS(0)N (143). The subsequent behavior of this nitrene suggests (Maricich and... 

Rhee and Shine39 used an impressive combination of nitrogen and carbon kinetic isotope effects to demonstrate that a quinonoidal-type intermediate is formed in the rate-determining step of the acid-catalyzed disproportionation reaction of 4,4 -dichlorohydrazobenzene (equation 26). When the reaction was carried out at 0°C in 60% aqueous dioxane that was 0.5 M in perchloric acid and 0.5 M in lithium perchlorate, extensive product analyses indicated that the major pathway was the disproportionation reaction. In fact, the disproportionation reaction accounted for approximately 72% of the product (compounds 6 and 7) while approximately 13% went to the ortho-semidine (8) and approximately 15% was consumed in the para-semidine (9) rearrangement. 

Another notable example of the anomalous behavior of imidazole ligands is the kinetic tram effect observed for the rates of substitution of 02 for CO in the hemes Fe(TPP)02L ([29], M = Fe, X = 02, L = Py, Pip, or l-Melm) according to Eq.(4)and Table 8 30). One of the three nitrogen donors in question, l-Melm, stabilizes the dioxygen adduct in a manner not to be expected from its basicity. The substitution is clearly of the SN1 type, the elimination of the 02 molecule being the rate-determining step. 

How does the rate-determining step relate to the rate law for the overall equation Consider the reaction of nitrogen dioxide with chlorine. 

A nitrogen isotope effect (1 006,1 010, and 1 006 at pH 6 73, 8 0, and 9 43) has been observed in the chymotrypsin-catalysed hydrolysis of NTacetyl-L-tryptophanamide which requires the C—N bond of the amide to be broken in the rate-determining step (O Leary and Kluetz, 1972). The isotope effect is similar to that observed for the reaction of amides with hydroxide ion which is known to proceed through a tetrahedral intermediate. 

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