CH10 Instructor Notes

CH10 Instructor Notes - UNIT 10 Conjugation in Alkadienes...

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Ch 221 Lecture Notes, Chapter 10 Page 1 of 7 UNIT 10 Conjugation in Alkadienes and Allylic Systems I. THE ALLYL SYSTEM A. Conjugated: Delocalization [Resonance] of electrons through a linear or cyclic array of p orbitals Conjugation results in stabilization of a pi bond or charge or a single electron. An orbital picture [Figure 10-1] B. Allylic carbocations are much more stable than alkyl carbocations Resonance is more stabilizing than hyperconjugation Cl H 2 O, Na 2 CO 3 OH OH 85% 15% Why this product distribution? [Mechanism 10.1] more stable RCl ROEt EtOH, 45°C (SN1) Cl Cl k rel 1 123
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Page 2 of 7 C. Allylic radicals Because allylic radicals are more stable, free-radical halogenation is easier to accomplish: [NBS when heated provides a low concentration of Br 2 ] Br No Reaction Free radical halogenation mechanism: [Mechanism 10.2] II . STRUCTURE AND PREPARATION OF DIENES A. Types: 1. Isolated dienes (alkadienes): Draw and name 1,4-pentadiene 1,5-cyclooctadiene
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This note was uploaded on 11/13/2010 for the course CH 221 taught by Professor Melander during the Fall '07 term at N.C. State.

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CH10 Instructor Notes - UNIT 10 Conjugation in Alkadienes...

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