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Organic Chemistry 6 th Edition Paula Yurkanis Bruice

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Chapter 18 Carbonyl Compounds II Reactions of Aldehydes and Ketones More Reactions of Carboxylic Acid Derivatives Reactions of a , b -Unsaturated Carbonyl Compounds. Organic Chemistry 6 th Edition Paula Yurkanis Bruice. Nomenclature of Aldehydes.

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Presentation Transcript
slide1

Chapter 18

Carbonyl Compounds II

Reactions of Aldehydes and Ketones

More Reactions of Carboxylic Acid Derivatives

Reactions of a,b-Unsaturated Carbonyl Compounds

Organic Chemistry

6th Edition

Paula Yurkanis Bruice

slide4

If a compound has two functional groups, the one with the

lower priority is indicated by its prefix:

slide5

Nomenclature of Ketones

The carbonyl is assumed to be at the 1-position in cyclic

ketones:

slide6

If a ketone has a second functional group of higher

priority…

A few ketones have common names:

slide7

The partial positive charge on the carbonyl carbon causes

that carbon to be attacked by nucleophiles:

An aldehyde has a greater partial positive charge on its

carbonyl carbon than does a ketone:

aldehydes are more reactive than ketones
Aldehydes Are More Reactive Than Ketones
  • Steric factors contribute to the reactivity of an aldehyde.
  • The carbonyl carbon of an aldehyde is more accessible
  • to the nucleophile.
  • Ketones have greater steric crowding in their transition
  • states, so they have less stable transition states.
slide10

Carboxylic acid derivatives undergo nucleophilic acyl

substitution reactions with nucleophiles:

slide11

Aldehydes and ketones undergo nucleophilic addition

reactions with nucleophiles:

This is an irreversible nucleophilic addition reaction if the nucleophile is a strong base

slide13

Formation of a New Carbon–Carbon

Bond Using Grignard Reagents

Grignard reagents react with aldehydes, ketones, and

carboxylic acid derivatives

slide17

+

+ NH3

Na

Reaction of Acetylide Ions with Carbonyl Compounds

slide21

Mechanism for the reaction of an ester with hydride ion:

Esters and acyl chlorides undergo two successive

reactions with hydride ion and Grignard reagents

slide23

The reduction of a carboxylic acid with LiAlH4 forms a

single primary alcohol:

Acyl chloride is also reduced by LiAlH4 to yield an alcohol

slide24

An amide is reduced by LiAlH4 to an amine

Mechanism for the reaction of an N-substituted amide

with hydride ion:

slide28

Compared with Grignard reagents and hydride ion, CN– is

a relatively weak base; therefore, in basic solution…

slide29

Aldehydes and ketones react with a primary amine to

form an imine:

This is a pH-dependent nucleophilic addition–elimination reaction

slide30

Dependence of the rate of the reaction of acetone with

hydroxylamine on the pH of the reaction: a pH-rate profile

Maximum rate is at pH = pKa of +NH3OH;

at this pH, both [H+] and [NH2OH] have the highest values

Decreasing rate: [H+] is decreasing

Decreasing rate: [NH2OH] is decreasing

Composition of the rate- determining step:

slide31

Aldehydes and ketones react with secondary amines to

form enamines:

An enamine undergoes an acid-catalyzed hydrolysis to

form a carbonyl compound and a secondary amine

slide36

Deoxygenation of the Carbonyl Group

Called the Wolff–Kishner reduction

slide40

The equilibrium constant for the reaction depends on the

relative stabilities of the reactants and products:

slide41

Addition of an Alcohol to

an Aldehyde or a Ketone

slide43

Utilization of Protecting Groups

in Synthesis

LiAlH4 will reduce the ester to yield an alcohol, but

the keto group will also be reduced

slide44

The keto group is protected as a ketal in this synthesis:

The more reactive aldehyde is protected with the diol

before reaction with the Grignard reagent:

slide50

The synthetically useful aldehyde anion does not exist

But its equivalent is accessible via the thioacetal:

slide51

Formation of Alkenes:

The Wittig Reaction

slide53

Preparation of the Phosphonium Ylide

The phosphonium ylide should be prepared from

sterically hindered alkyl halide:

Synthetic target:

Preferred synthetic approach:

slide54

The Wittig reaction is completely regioselective.

  • This reaction is the best way to make a terminal alkene.
  • Stable ylides form primarily E isomers, and unstabilized
  • ylides form primarily Z isomers.
  • Stable ylides have a group (C=O) that can share the
  • carbanion’s negative charge.

Example:

slide55

Stereochemistry of

Nucleophilic Addition Reaction

slide59

Disconnections, Synthons, and

Synthetic Equivalents

slide66

Nucleophiles that form unstable addition products form

  • conjugated addition products, because the conjugate
  • addition is not reversible.
  • Nucleophiles that form stable addition products can
  • form direct addition products or conjugate addition
  • products.
  • If the rate of direct addition is slowed down by steric
  • hindrance, a Grignard reagent will form the conjugate
  • addition product.
slide68

Strong bases form direct addition products with reactive

carbonyl groups and conjugate addition products with

less reactive carbonyl groups:

addition reactions to a b unsaturated carbonyls
Addition Reactions to a,b-Unsaturated Carbonyls
  • Michael addition nucleophiles:
  • Cyanide
  • Sulfide
  • Organocuprate
  • Amine
  • Halides
  • Direct addition nucleophiles:
  • Grignard
  • LAH
  • Organolithiums
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