Isotope Effects

and Molecular Vibrations

 

Two molecular vibrations for H3O+ + Styrene. 

The vibration representing the reaction coordinate:

 Another vibration, orthogonal to the reaction coordinate:
vib.xyz vib2.xyz

Zero-point energies (calculated at the PM3 level):

Reactants, all proteo 105.24 kcal/mol
Reactants,  OD 103.16 kcal/mol
Reactants,  vinyl-D3 99.493 kcal/mol

Impact (and interpretation)

Primary KIE:  always "normal" (kH/kD > 1)

isotop_5.gif (5362 bytes)

 Secondary KIE:  can be "normal or "inverse"
(kH/kD < 1)

isotop_4.gif (7091 bytes)

Observed KIEs:

isotop_1.gif (1445 bytes) 2-4
(dep. on pH, temp.)		 Primary (normal)
H/D transfer in rate-determining step
0.9
(0.948 per D)		 Secondary (inverse)
Rehybridization
isotop_3.gif (1791 bytes) 0.98 Secondary (inverse)
No change in hybridization; however, inductive stabilization by D vs. H.

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09/21/00