Ch_322a_6.02

Ch_322a_6.02 - molecule Generally the anions(conjugate bases of strong acids are good leaving groups H-A H 2 O H 3 O A-strong acid anion very

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Nucleophiles A nucleophile has an unshared pair of electrons available for bonding to a positive center. Nucleophiles may be negatively charged : HO:, CH 3 O:, :I:, :NH 2 - - - - : :: or neutral : H 2 O , H 3 N, CH 3 OH The polarity of the carbon-halogen bond determines the reactivity pattern: C X ! + ! " Nucleophiles attack electropositive center. Halide ion is the leaving group .
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Examples (1) HO: : - + C CH 3 Cl H H nucleophile substrate C CH 3 OH H H + Cl - product leaving group C CH 3 H H Cl (2) H-O H : + nucleophile substrate C CH 3 O-H H H H + + Cl leaving group ethyloxonium ion - product C CH 3 OH H H H 2 O + H 3 O +
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Leaving Groups The halogen is only one of many leaving groups , "L" . A more general description of nucleophilic substitution is Nu: + R- L - R-Nu + L: - leaving group A good leaving group produces a stable anion or neutral
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Unformatted text preview: molecule. Generally, the anions (conjugate bases) of strong acids are good leaving groups. H-A + H 2 O H 3 O + A: +-strong acid anion very stable A good leaving group in R-A . Neutral Molecules as Leaving Groups Poor leaving groups can be turned into good leaving groups by protonation . CH 3-OH Hydroxide ion is a poor leaving group because it is the anion of a weak acid , H 2 O. CH 3 OH : H 2 SO 4 + CH 3 OH H + + HSO 4 In the presence of a strong acid,-a nucleophilic substitution reaction occurs: CH 3 O: H nucleophile + CH 3 OH H + good leaving group CH 3 O H-CH 3 + + H 2 O leaving group...
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_6.02 - molecule Generally the anions(conjugate bases of strong acids are good leaving groups H-A H 2 O H 3 O A-strong acid anion very

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