Chapter 2 Linear Free Energy Relationship and Kinetic Isotope Effect - PowerPoint PPT Presentation

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Chapter 2 Linear Free Energy Relationship and Kinetic Isotope Effect

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When 0 r 1, the reaction is less sensitive to substituents ... P. Jr. Wentworth, A. Datta, S. Smith, A. Marshall, L. J. Partridge, and G. M. Blackburn, J. Am. ... – PowerPoint PPT presentation

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Title: Chapter 2 Linear Free Energy Relationship and Kinetic Isotope Effect


1
Chapter 2 Linear Free Energy Relationship and
Kinetic Isotope Effect
2
Substituent Effects
  • Field effects
  • Inductive effects
  • Resonance effects
  • Polarizability effects
  • Steric effects
  • Solvation effects

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Hammett Plots-- a general method for examining
changes in charges during a reaction.
  • Sigma values

KX
s log (KX/KH)
5
Hammett Plots
sr log (KX/KH) sr log (kX/kH)
  • Rho values
  • When rgt1lt the reaction under study is more
    sensitive to substitents than benzoic acid, and
    negative charge is building during the reaction.
  • When 0ltrlt1, the reaction is less sensitive to
    substituents than benzoic acid, but negative
    charge is still building
  • When r is equal to or close to 0, the reaction
    shows no substituent effects.
  • When r is negative, the reaction is creating
    positive charge.

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P. Jr. Wentworth, A. Datta, S. Smith, A.
Marshall, L. J. Partridge, and G. M. Blackburn,
J. Am. Chem. Soc., 1997, 119, 2315
10
J. P. Richard, and W. P. Jencks, J. Am. Chem.
Soc., 1982, 104, 4689.
11
J. Lehman, and G. C. Lloyd-Jones, Tetrahedron,
1995, 8863
12
Kinetic Isotope Effect
  • Stretching vibration
  • Bending vibration

n m-1/2
8
m reduced mass
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