SolomonsLKChapter6

SolomonsLKChapter6 - Chapter 6 Ionic Reactions-Nucleophilic...

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Chapter 6 Ionic Reactions-Nucleophilic Substitution and Elimination Reactions of Alkyl Halides
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Chapter 6 2 t Introduction The polarity of a carbon-halogen bond leads to the carbon having a partial positive charge In alkyl halides this polarity causes the carbon to become activated to substitution reactions with nucleophiles Carbon-halogen bonds get less polar, longer and weaker in going from Fuorine to iodine
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Chapter 6 3 Alkyl Halides and Nucleophilic Substitution The Polar Carbon-Halogen Bond
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Chapter 6 4 Alkyl Halides and Nucleophilic Substitution Three components are necessary in any substitution reaction. General Features of Nucleophilic Substitution
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Chapter 6 5 Alkyl Halides and Nucleophilic Substitution Negatively charged nucleophiles like HO ¯ and HS ¯ are used as salts with Li + , Na + , or K + counterions to balance the charge. Since the identity of the counterion is usually inconsequential, it is often omitted from the chemical equation. General Features of Nucleophilic Substitution When a neutral nucleophile is used, the substitution product bears a positive charge.
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Chapter 6 6 Alkyl Halides and Nucleophilic Substitution Furthermore, when the substitution product bears a positive charge and also contains a proton bonded to O or N, the initially formed substitution product readily loses a proton in a Br Ø nsted- Lowry acid-base reaction, forming a neutral product. General Features of Nucleophilic Substitution
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Chapter 6 7 t The Nucleophile A nucleophile may be any molecule with an unshared electron pair We ` ll discuss later what makes a nucleophile strong or weak (good or bad)
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Chapter 6 8 A leaving group is a substituent that can leave as a relatively stable entity It can either leave as an anion…. Leaving Groups …or as a neutral molecule
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Chapter 6 9 Alkyl Halides and Nucleophilic Substitution In a nucleophilic substitution reaction of R—X, the C—X bond is heterolytically cleaved, and the leaving group departs with the electron pair in that bond, forming X: ¯ . The more stable the leaving group X: ¯ , the better able it is to accept an electron pair. The Leaving Group
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Chapter 6 10 Alkyl Halides and Nucleophilic Substitution The Leaving Group
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Chapter 6 11 Alkyl Halides and Nucleophilic Substitution The Leaving Group
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Chapter 6 12 . Poor leaving groups can be turned into good leaving groups by protonation Hydroxide ion is a poor leaving group because it is the anion of a weak acid , H 2 O. CH 3 - OH : a nucleophilic substitution reaction occurs + CH 3 OH H + H 2 O leaving group nucleophile + good leaving group CH 3 OH + CH 3 O CH 3 H : + + + CH 3 OH H 2 SO 4 CH 3 OH H HSO 4 In the presence of a strong acid, Neutral molecules as leaving groups
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Chapter 6 13 l The Leaving Group The best leaving groups are weak bases which are relatively stable Other very weak bases (besides halide ions) which are good leaving groups:
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This note was uploaded on 12/22/2011 for the course CHEMISTRY 2210 taught by Professor Keller during the Spring '11 term at FIU.

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SolomonsLKChapter6 - Chapter 6 Ionic Reactions-Nucleophilic...

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