Ch11slides - Chapter 11: Nucleophilic Substitution and...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Chapter 11: Nucleophilic Substitution and Elimination Walden Inversion O OH OH HO O ( S )-(-) Malic acid [ α ] D = -2.3 ° PCl 5 O Cl OH HO O Ag 2 O, H 2 O O OH OH HO O ( R )-(+) Malic acid [ α ] D = +2.3 ° PCl 5 Ag 2 O, H 2 O O Cl OH HO O (+)-2-Chlorosuccinic acid (-)-2-Chlorosuccinic acid The displacement of a leaving group in a nucleophilic substitution reaction has a defined stereochemistry Stereochemistry of nucleophilic substitution p-toluenesulfonate ester (tosylate): converts an alcohol into a leaving group; tosylate are excellent leaving groups. abbreviates as Tos C X Nu: C Nu + X - X= Cl, Br, I C OH S O O Cl CH 3 + C O S O O CH 3 tosylate C O S O O CH 3 Nu: C Nu S O O - O CH 3 +
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 The nucleophilic substitution reaction “inverts” the Stereochemistry of the carbon (electrophile)- Walden inversion O H Tos-Cl pyridine O H H Tos [ α ] D = +33.0 H 3 C O - O H O O CH 3 [ α ] D = +31.1 [ α ] D = -7.06 + Tos O - HO - H O H [ α ] D = -33.2 Tos-Cl pyridine H O Tos [ α ] D = -31.0 H 3 C O - O O H O CH 3 HO - Tos O - + [ α ] D = -7.0 Kinetics of nucleophilic substitution Reaction rate: how fast (or slow) reactants are converted into product (kinetics) Reaction rates are dependent upon the concentration of the reactants. (reactions rely on molecular collisions) Consider: At a given temperature: If [OH - ] is doubled, then the reaction rate may be doubled If [CH 3 -Br] is doubled, then the reaction rate may be doubled A linear dependence of rate on the concentration of two reactants is called a second-order reaction (molecularity) C Br H H H HO _ C HO H H H Br _
Background image of page 2
3 C Br H H H HO _ C HO H H H Br _ Reaction rates (kinetic) can be expressed mathematically: reaction rate = disappearance of reactants (or appearance of products) For the disappearance of reactants: rate = k [CH 3 Br] [OH - ] [CH 3 Br] = CH 3 Br concentration [OH - ] = OH - concentration k= constant (rate constant) For the reaction above, product formation involves a collision between both reactants, thus the rate of the reaction is dependent upon the concentration of both. L mol•sec Nucleophilic Substitution comes in two reaction types: S N 2 S N 1 S= substitution S= substitution N= nucleophilic N= nucleophilic 2= biomolecular 1= unimolecular rate = k [R-X] [Nu:] rate = k [R-X]
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 The S N 2 Reaction: Mechanism Steric effects in the S N 2 reaction: For an S N 2 reaction, the nucleophile approaches the electrophilic carbon at an angle of 180 ° from the leaving group (backside attack) the rate of the S N 2 reaction decrease as the steric hindrance (substitution) of the electrophile increases.
Background image of page 4
5 C H 3 C CH 3 CH 3 Br C H 3 C CH 3 CH 3 CH 2 Br C H 3 C CH 3 H Br C H CH 3 H Br C H H H Br tertiary neopentyl secondary primary methyl < < < < realtive
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/11/2012 for the course CHEM 220A taught by Professor Sulikowski during the Fall '08 term at Vanderbilt.

Page1 / 19

Ch11slides - Chapter 11: Nucleophilic Substitution and...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online