SUBSUpdate - Competitive Reactions Elimination,...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
SUBSTITUTION REACTIONS S N 1 S N 2 Mechanisms Two step R-Nu fast Nu: slow R + R-X One step NuR + :X Nu: + R-X Kinetics 1st order (unimolecular) Rate = k[R-X] Ionization = rate determining step (2nd step does not affect rate) 2nd order (bimolecular) Rate = k[Nu:][R-X] Stereochemistry Predominant Racemization Inversion Solvent Effects Requires an ionizing solvent (polar protic) such as H 2 O, CH 3 OH, CH 3 CH 2 OH, HCO 2 H, CH 3 CO 2 H Variety of solvents OK. Nonpolar solvent favors S N 2 by supressing S N 1. Often faster in less polar solvent because strong solvation weakens the strength of the nucleophile. Polar aprotic solvents are particularly good: CH 3 CN, O CH 3 CCH 3 O CH 3 SCH 3 O HCN(CH 3 ) 2 , Effect of R tert. >> sec. > pri. Resonance stabilization favors reaction Steric hindrance control CH 3 > pri. > sec. (tert. = 0)
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Competitive Reactions Elimination, rearrangement Elimination by strongly basic nucleophiles Leaving Groups (X:, XH) Good leaving group required Good leaving groups are weak bases. Good leaving groups: OSO 2 R, I , Br , O OC R Cl , H 2 O, ROH, N 2 , Trends: I > Br > Cl >> F Never leaving groups: HO , RO , H , R 3 C , R 2 N Good leaving group required Nucleophile (Nu:) or Base (B:) Weak nucleophiles are OK. S N 1 reaction is favored by weak nucleophiles by supressing S N 2. Good nucleophile required. Good nucleophiles: I-, Br-, Cl-, RO-, HO , RS , RCO 2 , NO 2 , N 3 , R 2 N , R 3 N Weak nucleophiles: H 2 O, ROH, RCO 2 H...
View Full Document

This note was uploaded on 11/23/2010 for the course CHEMISTRY Chem 51A taught by Professor Dr.susanm.king during the Fall '10 term at UC Irvine.

Ask a homework question - tutors are online