Determining transition state structure using kinetic isotope effects

Abstract

Kinetic isotope effects (KIEs) have been found to be the most powerful tool available to physical organic chemists for determining the mechanism of reactions and for estimating the structure of their transition states. Various types of KIEs including primary-leaving group-, nucleophile-, and a-carbon KIEs and secondary alpha-and beta-deuterium KIEs are introduced. The factors that affect the magnitude of each of these KIEs are covered in some detail. Finally, the use of these KIEs to determine the mechanism of a reaction and to estimate the structure of the transition state for a reaction is discussed.

Secondary kinetic deuterium isotope effect in oxidative addition reaction of cycloplatinated(II) complexes with MeI

“…We, however, have lately reported that KIE values in reactions of the Pt(II) complex [PtMe 2 (2,2 0 -bipyridine)] with CH 2 RX reagents (in which R ¼ H [14], CH 3 [13], or Ph [16]) are significantly dependent on R and a high value is obtained when R is CH 3 or Ph. The latter cases have been described [13,16] as the presence of bulkier alkyl halides and creation of more room for the CaÀH(D) out-of-plane bending vibration [34]. We therefore have come to the conclusion that in oxidation addition reactions of organoplatinum(II) complexes with alkyl halides, nature of the Pt complex has a minor influence, while that of bulkiness of the alkyl halides has a significant influence on the resulting KIE values.…”

Mechanistic investigations of the hydrolysis of amides, oxoesters and thioesters via kinetic isotope effects and positional isotope exchange

“…The physical origin of KIEs is a complex subject and the theory has advanced steadily over the years [6][7][8][9]. This topic will be discussed elsewhere in this special issue.…”

Factors affecting enzyme activity

“…Adding to these ideas is the isotope effect which is one of the most powerful techniques available to determine the structure of the transition state (Westaway, 2007). The Hammond postulate theorizes that intermediates of a unimolecular reaction that are similar in energy to the transition state are also structurally similar.…”