Ch_322b_20.04

Ch_322b_20.04 - Effect of Substituents on the Basicity of...

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Effect of Substituents on the Basicity of Anilines Substituents, especially those that are electron-withdrawing, influence the basicity of anilines. The substituent effect is important in both the free base and conjugate acid. NH 2 : G + H 2 O K b NH 3 G + + HO - free base conjugate acid When G is electron-releasing, the free base is destabilized while the conjugate acid is stabilized leading to a smaller (less positive) standard enthalpy change ( ! H o ), and a larger value for K b . When G is electron-withdrawing, the free base is stabilized while the conjugate acid is destabilized leading to a larger (more positive) standard enthalpy change ( ! H o ), and a smaller value for K b .
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An Energy Diagram Description of the Substituent Effects enthalpy NH 2 H free base conjugate acid ! H o H 3.8 x 10 -10 K b NH 2 CH 3 ! H o CH 3 14.8 x 10 -10 p-CH 3 NH 2 NO 2 0.01 x 10 -10 ! H o NO 2 p-NO 2 strongest base weakest base
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Stereoelectronic Effects: Sorting out Resonance and Inductive Influences The relative importance of resonance (
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_20.04 - Effect of Substituents on the Basicity of...

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