1. Chemistry 125: Lecture 48 February 8, 2010 Addition to Alkenes a Physical-Organic MO Perspective This For copyright notice see final page of this file

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3. Butenes Combustion of 4 C graphite + 8 H H-H gives 607.5 kcal/mole http://webbook.nist.gov/chemistry/

4. Use NIST Webbook to study factors influencing relative stability of butenes For high precision convert to a common product, butane, using catalytic hydrogenation, which is fast and clean, and much less exothermic than combustion.

5. Isomeric Hexenes  H f Problem: Are these data consistent with those for the butenes?

6. C 6 H 12 Alkene Isomer Stability 2.8 3.6 2.5 2.6 7.7 -12 -10 -14 -16 -18 -20 -22  H f (kcal/mol) Strain Energy (MM2) sp 2 C-H  sp 2 C-C ~2.5 kcal/mol cis  trans ~1.5 kcal/mol  H f from Pedley (1994) 3214 # of C - C= bonds Cf. Table 10.1, p. 413

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8. H  * LUMO  HOMO orthogonal Addition to Alkenes SOMO : Radical Chain H-Br Br CC CC CC H H Br HOMO/LUMO : Concerted CC H CC H H  * LUMO  HOMO CCCC  * LUMO  HOMO HOMO/LUMO : Stepwise “Electrophilic” (“works” with Pt/C Catalyst! Sec 10.2, 410ff ) (Section 11.4-11.5, 481-488 Regioselective) Br-H CC CC H Br CC H + (for any H-Hal Ch. 3, Ch. 9) (Markovnikov) HOMO-HOMO repulsive empty C C Br H C C H

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10. -22 kcal/mole +17 kcal/mole Surface Potential (energy of proton on van der Waals surface) Electrostatics is important in positioning fragments, but new bonding requires orbital mixing. Electrophilic Addition to Alkenes. Sec. 3.16-3.19 HX addn via R + Energetics Regiochemistr y (Markovnikov) Hydration R + + H 2 O

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12. Section 9.1-9.7 Addition of Hydrogen Halides 9.3 148 Regioselectivity 9.5 374 Intermediate Cations 9.6 366; 10.6 445 Cation Stability 9.9 386-9 Cation Rearrangement

13. Loudon 4.7C 151-4 Cation Stability (source?) 1° to 2°  = 21 kcal/mole vs. 2.5 kcal/mole for n-alkenes Table 10.2 p. 445 Compared to what?

16. Doubleor ? CC H CC H CC H MinimumSingle HOMO-1 LUMO HOMO LUMO+1 “Hyperconjugation” (  HOMO-LUMO mixing) CC H CC H CC H CC H

17. CCCCCC H 2 CH Doubleor ?MinimumSingle LUMO+1 HOMO H H H

18. CH 3 CCCCCC H 2 CH Doubleor ?MinimumSingle “ ” LUMO+1 HOMO-7

19. 9.9 386-9 Cation Rearrangement do Problem 9.11 (ring expansion)

20. End of Lecture 48 Feb. 8, 2010 Copyright © J. M. McBride 2010. Some rights reserved. Except for cited third-party materials, and those used by visiting speakers, all content is licensed under a Creative Commons License (Attribution-NonCommercial-ShareAlike 3.0).Creative Commons License (Attribution-NonCommercial-ShareAlike 3.0) Use of this content constitutes your acceptance of the noted license and the terms and conditions of use. Materials from Wikimedia Commons are denoted by the symbol. Third party materials may be subject to additional intellectual property notices, information, or restrictions. The following attribution may be used when reusing material that is not identified as third-party content: J. M. McBride, Chem 125. License: Creative Commons BY-NC-SA 3.0