Pseudo lirst order conditions

Jencks and Richard, and others, had pioneered the use of the azide elock to quantitatively assess the lifetime of carbenium ions generated under solvolytic conditions. The method relies on the use of product yield data collected at varying [N3 ] to determine the N /solvent selectivity, expressed as the ratio of the second-order rate constant for trapping of the ion by N3 and the pseudo-lirst-order rate constant for trapping of the ion by solvent k Jk. The assumption is made that k z is diffusion limited at ca. 5 x 10 M"" s This assumption allows k to be estimated, and l/kg provides the lifetime of the ion in the solvent in the absence of added nucleophiles. McClelland and Steenken showed by direct measurement of k. , for a series of diarylmethyl and triarylmethyl carbocations that k is approximately constant at... 

The plots of pseudo-lirst-order rate constants (k bs) for the reactions between anionic 6-0-octanoyl-L-ascorbic acid (VC8) and 3-methylbenzenediazonium cation (3MBD), under reaction conditions of apparent constant pH and [3MBD] [VC8], vs. [micelles] (micelles of SDS, CTABr, and TTABr) show distinct maxima with > 3 for SDS and > 11 for CTABr as well as TTABr... 

Ihe conditions chosen make the reaction appear to be lirst-order overall, although the reaction is realty not first-order overall, unless t and . happen to he zero. The pseudo-hrst-order rate constant is related to the k in the originally postulated rate law by... 

---

See also in sourсe #XX -- [ ]

---