ho5 - Heres generally a good rule: Ask yourself these...

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Table 7-4 Likely Mechanisms by Which Haloalkanes React with Nucleophiles (Bases) Type of Nucleophile (Base) Poor nu- Weakly Basic Strongly Basic, Strongly basic, Type of Haloalkane good nu- unhindered nu- hindered nu- Methyl no rxn Sn2 Sn2 Sn2 Primary Unhindered no rxn Sn2 Sn2 E2 Branched no rxn Sn2 E2 E2 Secondary Slow Sn1/E1 Sn2 E2 E2 Tertiary Sn1/E1 Sn1/E1 E2 E2 Handout #5 Friday 12pm-12:50pm TA: Winnie Chan OH: Friday 1:00pm-1:50pm Strong Nu- (usually anions with full negative charge) - S-H - S-CH 3 (weak base) - O-H - O-CH 3 NH 3 N(CH 3 ) 3 NH(CH 2 CH 3 ) 2 P(CH 3 ) 3 (weak base) I - Br - (weak base) - CN N 3 - (weak base) Weak Nu- usually neutral molecules H-S-H CH 3 -S-CH 3 H-O-H H-O-CH 3 F - Cl - CH 3 COO - LiC(CH 3 ) 3 (strong base) KOC(CH 3 ) 3 (strong base) *Know this chart! Understand why it is how it is! This is a brief guide of strong/weak nucleophiles. Not all inclusive Deciding between Substitution and Elimination?
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Unformatted text preview: Heres generally a good rule: Ask yourself these questions: 1. Is the nucleophile a strong base? 2. Is the nucleophile sterically hindered? 3. Is the substrate sterically hindered? (tertiary, secondary, primary branched) *if you have at least 2 yess to the questions, elimination. If not, substitution. 5. Draw a reasonable mechanism for the reaction below. Br > OCH 2 CH 3 +HBr CH 3 CH 2 OH 6. Draw all of the isomers, including stereoisomers of C 5 H 8 Cl 2 which contain a cyclopentane ring. Label any compounds whih are meso stereoisomers and label pairs of enantiomers. 7. Draw reasonable mechanism for the transformation below. Be sure to account for stereochemical outcome of the reaction. OH OSO 2 CH 3 H Base Polar aprotic solvent > O CH 3 H...
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This note was uploaded on 01/25/2010 for the course CHEM chem 140A taught by Professor Dr.yang during the Spring '07 term at UCSD.

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ho5 - Heres generally a good rule: Ask yourself these...

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