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OrganicFallChpt10 - Chapter 10 Homework Due All in-chapter...

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Chapter 10 Homework Due 11/8/02 All in-chapter problems End of chapter problems: 18, 22-24, 26, 30 Bonus problems: React the following starting molecules with the given reactants and show the expected products. All are Diels Alder reactions. NO 2 C H 3 CO O H H Br Br Br Br H O 2 N H NO 2 H 3 C H 3 CO CN CN
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Chapter 10: Dienes Allyl groups Essentially a group adjacent to a double or triple bond The sp 3 hybridized center is called the allylic carbon An allylic substituent is attached to the allylic carbon Carbocations adjacent to a double bond are allylic Carbocation is a p orbital Electrons share from double bond into carbocation, stabilizing it. Even more stable than tertiary carbocation R 2 C C R C H 2 Allylic methylene
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Electron movement Carbocation exists on two carbons due to the speed of electron migration Resonance structure - shows movement of electrons and movement of electron rich or electron poor locations Allylic anions do the same thing Charges will reside on a carbon where the charge is most stabilized Tertiary for carbocations Primary for carbanions Free radicals are also stabilized R 2 C C R C H R 2 C C R C H R 2 C C R C H R 2 C C R C H R 2 C C R C H R 2 C C R C H
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Allylic reactions Free radical additions of chlorines Book talks about them, but they occur at low concentrations in a gas phase. Synthetically useless Instead, use N-bromosuccinimide for allylic halogenation NBS Looks like this --> Reactions: Mechanism NBr O O NBr O O + NH O O + Br heat or light CCl 4 NH O O N O O H Br heat or light CCl 4 N O O Br N O O Br Br
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Dienes Three types Isolated dienes Conjugated dienes Cumulated dienes (allenes) Stability 1,4-pentatdiene 252 kJ/mol 1,3-pentadiene 226 kJ/mol 1,2-pentallene 412 kJ/mol The delocalized pair of double bonds is most stable Allenes are quite reactive Notice the center carbon of an allene is sp hybridized!
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