Stopped-flow nucleophilic addition

Such nucleophilic displacements are likely to be addition-elimination reactions, whether or not radical anions are also interposed as intermediates. The addition of methoxide ion to 2-nitrofuran in methanol or dimethyl sulfoxide affords a deep red salt of the anion 69 PMR shows the 5-proton has the greatest upfield shift, the 3- and 4-protons remaining vinylic in type.18 7 The similar additions in the thiophene series are less complete, presumably because oxygen is relatively electronegative and the furan aromaticity relatively low. Additional electronegative substituents increase the rate of addition and a second nitro group makes it necessary to use stopped flow techniques of rate measurement.141 In contrast, one acyl group (benzoyl or carboxy) does not stabilize an addition product and seldom promotes nucleophilic substitution by weaker nucleophiles such as ammonia. Whereas... 

The electrophilic reactions of NP with SH- and several SR- have been studied and reviewed (28). The nature of the reversible addition reactions [Eq. (5)] are reasonably well understood for the thiolates. A kinetic study including some bioinorganically relevant nucleophiles (cysteine, glutathione) was performed by using stopped-flow and T-jump techniques (77). The rate constants for the forward and reverse processes in Eq. (5) were in the range 103-104 M-1 s-1 and 101 K)3 s-1 at 25 °C, respectively. 

What is the precise mechanistic process by which bromine (and by extension chlorine) adds to alkenes Studies designed to probe this question are generally difficult to conduct due to the very fast product-forming steps. By applying stopped-flow spectrokinetics to sterically crowded alkenes such as adamantylideneadamantane (Ad2>, where steric hindrance retards the final addition step by hampering rearside nucleophilic attack of the counterion at the bromonium carbons of the intermediate ion pairs, it... 

The order of reactivity of picryl halides is the reverse of that observed in the reactions of the corresponding alkyl halides.1 Alkyl fluorides react only slowly with nucleophiles whereas picryl fluoride reacts extremely rapidly with hydroxide ions to produce picric acid. Addition of sodium hydroxide to a picryl halide in aqueous dioxan produces a transient red intermediate. The present study has been concerned with the measurement of the rates of formation and decay of the intermediates derived from picryl fluoride, chloride and bromide using stopped-flow spectrophotometry. The spectra of the intermediates are similar to those attributed to Meisenheimer complexes. Picryl fluoride reacts to give this intermediate in a few milliseconds. The rate of appearance of the intermediate was therefore only measurable at very low base concentrations (less than 6 x 10 M hydroxide). Under these conditions the rate was found to... 

Several kinetic studies of nucleophilic attack upon coordinated car-benes have appeared. Particularly revealing has been a stopped-flow investigation of the addition of PBu and P(OBu")3 to the carbene carbon in the chromium triad carbenes, [M(CO)sCR (OEt)] (M = Cr, Mo, or W R = Ph or Me) [equation (1)]. The forward rate constant, ki, is little... 

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