L19a - Draw MOP SN2 product R NaOCH3 NaSH SN2 mechanism...

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1 1 Configuration? 1. R 2. S R S 86 % 14 % © Kay Sandberg Draw MOP S N 2 product Br NaOCH 3 ppp Na NaSH SH MOP Is MOP R or S? 2 © Kay Sandberg Section 8.4 S N 2 mechanism Substitution bimolecular nucleophilic OH 1- + CH 3 Br HOCH 3 + Br 1- Observed rate is second order over all 1 st order in nucleophile & 1 st order in substrate Rate = k[ OH 1- ][ CH 3 Br ] 3 C Br O + H H H H Br O + C H H H H Concerted rxn: © Kay Sandberg Section 8.5 S N 2 mechanism Direct displacement stereospecific stereospecific (back-side) HO Br C δ - δ - H H H Transition state •single elementary step •one transition state •bimolecular •second order overall OH 1- , CH 3 Br CH 3 OH, Br 1- TS E Reaction Coordinate 4 C Br O + H H H H Br O + C H H H H Br C δ - δ - H H H Transition state © Kay Sandberg Section 8.5 S N 2 mechanism bond “makeage” bond “breakage” 5 C H Br S R © Kay Sandberg 6 C H Br δ− S R δ− © Kay Sandberg
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2 7 C H Br δ− S R δ− © Kay Sandberg 8 C H Br δ− S R δ− © Kay Sandberg 9 Configuration? R S 95 % 5% 1. R 2. S S R C H Br © Kay Sandberg What is the configuration of the chiral carbon ? 1 2 3 Focus on the methyl group as the Nu and LG bonds are kept in plane of screen. 10 C H Br S R © Kay Sandberg 11 C H Br δ− S R δ− © Kay Sandberg 12 C H Br δ− S R δ− © Kay Sandberg
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3 13 C H Br δ− S R δ− © Kay Sandberg 14 S R C H Br © Kay Sandberg 15 C H Br © Kay Sandberg When Nu and LG bonds are in the plane of screen, inversion of configuration occurs as the methyl , ethyl and H keep their bond characteristics (i.e., wedge stays wedge), but switch their angle (all initially leaned to left, ended up leaning to right) . C H Br S R S S R R 16 © Kay Sandberg When Nu and LG bonds are not in the plane of screen, inversion of configuration occurs when the Nu has the opposite bond characteristic of the LG S R Br S R Br 17 Configuration? © Kay Sandberg Draw MOP S N 2 product Br NaOCH 3 Major S N 2product O O X 18 © Kay Sandberg Section 8.1 Nucleophilic Substitution (NS) Functional Group Transformation by NS R X Alkyl halide Prepared from: Alkanes - free radical halogenation Alcohols - nucleophilic substitution Alkenes - hydrohalogenation δ + δ - I, Br, Cl
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4 19 © Kay Sandberg Section 8.1 Nucleophilic Substitution (NS) Functional Group Transformation by NS XX X sp 3 sp 2 sp 2 Alkyl halide Alkenyl halide (vinylic halide) Aryl halide Unreactive under NS conditions 20 © Kay Sandberg Section 8.2 Nucleophilic Substitution (NS) Also the order of reactivity for elimination rxns R F R Cl R Br R I Increasing rate of substitution by nucleophiles Poorest leaving group Weakest C-X bond Most basic Least basic Strongest C-X bond Best leaving group << < < 21 © Kay Sandberg Section 8.1 Nucleophilic Substitution (NS) Functional Group Transformation by NS Halide-halide exchange Y R X Y R X + halide ion alkyl halide alkyl halide halide ion 22 © Kay Sandberg Section 8.1 Nucleophilic Substitution (NS) Halide-halide exchange Br CH 3 CH 2 CH 2 CH 2 CH 2 F K + F Br + CH 3 CH 2 CH 2 CH 2 CH 2 K + + ethylene glycol 120 o Le Châtelier’s principle: •C-F bond stronger than C-Br
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This note was uploaded on 03/30/2009 for the course CH ORGANIC CH taught by Professor Kaysandberg during the Spring '09 term at N.C. State.

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L19a - Draw MOP SN2 product R NaOCH3 NaSH SN2 mechanism...

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