lecture 20 (ch 9) - Organic Lecture Series CH 310/318 M...

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Organic Lecture Series 1 CH 310/318 M LECTURE 20 Textbook Assignment: Chapter 9- Nucleophilic Substitution and β -elimination Today’s Topics: Sn1 and Sn2 Reaction Mechanisms Sn1 and Sn2 Reaction Mechanisms Notice & Announcements: Office moved to WEL 4.242 Organic Lecture Series 2 Nucleophilic Nucleophilic Substitution Substitution and and β β - - Elimination Elimination Chapter 9 Chapter 9
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Organic Lecture Series 3 Nucleophilic Nucleophilic Substitution Substitution Nucleophile Nucleophile : From the Greek meaning nucleus loving. A molecule or ion that donates a pair of electrons to another atom or ion to form a new covalent bond; a Lewis base. Nucleophilic Nucleophilic substitution: substitution: Any reaction in which one nucleophile substitutes for another at a tetravalent carbon. CN u CL v Nu Lv nucleophilic substitution Nucleophile + + Leaving group Organic Lecture Series 4 • Electrostatic potential map showing the nucleophile (OH - ) reacting at its negative (red) end with the electrophilic carbon (blue) in the reaction of hydroxide with chloromethane. Nucleophilic Nucleophilic Substitution Substitution
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Organic Lecture Series 5 I HS - RO CN HO HC C Nu NH 3 HOH CH 3 I CH 3 SH CH 3 OH CH 3 OR CH 3 O-H H CH 3 Br CH 3 CH 3 CC H CH 3 NH 3 + CH 3 Nu Br + an alcohol (after proton transfer) an alkylammonium ion an alkyl iodide a nitrile an alkyne a thiol (a mercaptan) an ether an alcohol Reaction: + + : Nucleophilic Nucleophilic Substitution Substitution - Haloalkanes Haloalkanes Organic Lecture Series 6 • Chemists propose two limiting mechanisms for nucleophilic substitution. –A fundamental difference between them is the timing of bond- breaking and bond-forming steps. Mechanisms Mechanisms
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Organic Lecture Series 7 • At one extreme, the two processes take place simultaneously; designated S N 2. –S = substitution –N = nucleophilic –2 = bimolecular (two species are involved in the rate- determining step) Mechanisms Mechanisms Organic Lecture Series 8 – Both reactants are involved in the transition state of the rate-determining step. CB r H H H HO: - + C H H H HO Br δ - δ - Transition state with simultaneous bond breaking and bond forming C H H H HO + Br : :: : : Mechanisms S Mechanisms S N 2
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Organic Lecture Series 9 • An energy diagram for an S N 2 reaction. There is one transition state and no reactive intermediate.
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This note was uploaded on 03/20/2011 for the course CHEMISTRY 310m taught by Professor Iverson during the Fall '08 term at University of Texas.

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lecture 20 (ch 9) - Organic Lecture Series CH 310/318 M...

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