TTh_12 - Organic Lecture Series CH 310/318 M Textbook...

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Organic Lecture Series 1 CH 310/318 M LECTURE 12 Textbook Assignment: Chapter 6 Today’s Topics: Alkene Alkene - addition reactions addition reactions Notice & Announcements: HW 4 due Monday Organic Lecture Series 2 Reactions Reactions of Alkenes of Alkenes Chapter 6 Chapter 6
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Organic Lecture Series 3 HBr HBr + 2 + 2 -Butene Butene • A two-step mechanism Step 1: Proton transfer from HBr to the alkene gives a carbocation intermediate. Step 2: Reaction of the sec- butyl cation (an electrophile) with bromide ion (a nucleophile) completes the reaction. CH 3 CH=CHCH 3 HB r 3 CH-CHCH 3 H Br + + δ− δ+ slow, rate determining sec-Butyl cation a 2° carbocation 3 CHCH 2 3 3 2 3 + fast Bromide ion (a nucleophile) sec-Butyl cation (an electrophile) 2-Bromobutane Br Organic Lecture Series 4 An energy diagram for the two-step addition of HBr to 2-butene. – The reaction is exergonic. HBr HBr + 2 + 2 -Butene Butene
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Organic Lecture Series 5 Addition of HX Addition of HX • Carried out with pure reagents or in a polar solvent such as acetic acid . • Addition is regioselective – Regioselective Regioselective reaction: reaction: An addition or substitution reaction in which one product is formed in preference to all others that might be formed. Markovnikov Markovnikov ’s rule: rule: In the addition of HX or H 2 O to an alkene, H adds to the carbon of the double bond having the greater number of hydrogens. 1-Bromopropane (not observed) 2-Bromopropane Propene + + CH 3 CH=CH 2 HBr 3 CH-CH 2 H 3 2 Br Br H Organic Lecture Series 6 Carbocations Carbocations Carbocation Carbocation : A species in which a carbon atom has only six electrons in its valence shell and bears a positive charge.
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This note was uploaded on 03/18/2012 for the course CH 310 M taught by Professor Iverson during the Spring '09 term at University of Texas at Austin.

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TTh_12 - Organic Lecture Series CH 310/318 M Textbook...

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