Transition state structure, secondary deuterium isotope effects and

Tetrahedral intermediates, derived from carboxylic acids, spectroscopic detection and the investigation of their properties, 21, 37 Topochemical phenomena in solid-state chemistry, 15, 63 Transition state structure, crystallographic approaches to, 29, 87 Transition state structure, in solution, effective charge and, 27, 1 Transition state structure, secondary deuterium isotope effects and, 31, 143 Transition states, structure in solution, cross-interaction constants and, 27, 57 Transition states, the stabilization of by cyclodextrins and other catalysts, 29, 1 Transition states, theory revisited, 28, 139... 

Transition state analysis using multiple kinetic isotope effects, 37, 239 Transition state structure, crystallographic approaches to, 29, 87 Transition state structure, in solution, effective charge and, 27, 1 Transition state structure, secondary deuterium isotope effects and,... 

Transition stale structure, secondary deuterium isotope effects and, 31, 143 Transition states, structure in solution, cross-interaction constants and, 27, 57 Transition states, the stabilization of by cyclodextrins and other catalysts, 29, 1 Transition states, theory revisited, 28, 139... 

Fig. 10.12 (a) Transition state structures (C—C bond lengths) calculated at two levels for the concerted and step-wise Diels-Alder reaction shown in Fig. 10.11 (Houk, K. N., Gonzalez, J., and Li, Y,Accts. Chem. Res. 28, 81 (1995). The parenthesized values show results for calculations at a much higher (and much more expensive) level, (b) Calculated secondary deuterium isotope effects, kH/kD (per D) for the concerted and stepwise Diels-Alder reactions shown in Fig. 10.11 (Houk, K. N., Gonzalez, J., and Li, Y,Accts. Chem. Res. 28, 81 (1995). The parenthesized values show results for calculations at a much higher (and much more expensive) level)...

Hanzlik, R.P. and G.O. Shearer (1975). Transition state structure for peracid epoxidation Secondary deuterium isotope effects. J. Am. Chem. Soc. 97, 5231-5233. 

Deuterium kinetic isotope effects, secondary, and transition state structure, 31,143 Diazo compounds, aliphatic, reactions with acids, 5, 331... 

Secondary Deuterium Kinetic Isotope Effects and Transition State Structure... 

This corresponds to an isotope effect of approximately 3.5% per deuterium. In comparison, the secondary /3-deuterium KIEs in SN1 reactions are all normal and range from 5% to 15% per deuterium. Because the normal KIEs in SN1 reactions result from the weakening of the C,—L bond by a hyperconjugative interaction with the incipient carbocation in the transition state, the authors concluded that hyperconjugative interactions are present also in the transition state for the insertion reaction. The normal secondary /3-deuterium KIE observed for the insertion reaction is consistent with the dipolar three-centre transition state structure [15] proposed by Seyferth et al. (1970a,b) because the partial positive charge on the a-carbon is stabilized by hyperconjugation. 

TABLE 17. The secondary alpha deuterium and primary leaving group nitrogen kinetic isotope effects and the relative transition state structures for the ion-pair S 2 reactions between sodium thiophenoxide and benzyldimethylphenylammonium nitrate in DMF at different ionic strengths at 0°C... 

Ab initio calculations at the MP2/6-31+ G level have been performed for gas-phase El elimination reactions of CH3CH2X (X = NH3"1", Br, Cl, F, SH) promoted by NH . OH-, F-, PH2. SH-, and Cl- in order to determine how changes in transition-state geometry, from reactant-like to product-like, influence kinetic isotope effects.9 Secondary isotope effects (a-H) on leaving group departure are correlated with the hybridization at C7 in the transition state, whereas there is no such correlation between secondary (/5-H) isotope effects and the transition state hybridization at C/ . The primary deuterium isotope effect is influenced markedly by the nucleophilic atom concerned but approach to a broad maximum for a symmetric transition structure can be discerned when due allowance is made for the element effect. 

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