Organic test 2

Organic test 2 - Exam Paper

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Chaps 15-17 Review
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Chapter 15. 1. Basic Concepts • Conjugated system (Resonance energy) • Constructing MOs of conjugated system • Kinetic vs thermodynamic control: 1,2- vs 1,4-addition • The allylic system • The Diels-Alder reactions 2
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3 Conjugated System • Alternating mutiple (double and/or triple) and single bonds. • Interrupted by sp 3 hybridized atoms
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Some Conjugated Molecules
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Resonance Energy • Heat of hydrogenation for trans -1,3-pentadiene is less than expected. Δ H for 1-pentene is 30.0 kcal/mol and for trans -2- pentene is 27.4 kcal/mol, so expect 57.4 kcal for trans -1,3-pentadiene. • Actual Δ H is 53.7 kcal, so the conjugated diene is more stable. Difference, (57.4 – 53.7) 3.7 kcal/mol, between conjugated and isolated systems, is the resonance energy . 5
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Constructing MOs of Conjugated System 6 • Based on side-by- side overlap of p orbitals on sp 2 or sp hybridized atoms. • Involving all possible (phase) recombinations of the p -orbitals. • The allylic systems
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Kinetic vs Thermodynamic Control 7 Kinetic control : the distribution of products is determined by the relative rate of formation of each product Thermodynamic control : for a reaction under thermodynamic control, the distribution of products is determined by the relative stabilities of each product • Review mechanism of 1,2- and 1,4- electrophilic addition of 1,3-conjugated diene
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8 1 2 3 4 2 1 4 1 H H kinetic thermodynamic CH 2 =CH-CH=CH 2 H Br CH 2 =CH-CHCH 2 Br BrCH 2 -CH=CH-CH 2 forms more rapidly is more stable
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Major product at 40 ° C Major product at -80 ° C 9 The addition of Br 2 to a butadiene follows the same trend.
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This note was uploaded on 11/10/2010 for the course CHE 201 taught by Professor Bong during the Spring '08 term at SUNY Buffalo.

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Organic test 2 - Exam Paper

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