Aldehyde Ketone 1

8/19/2019 Aldehyde Ketone 1

1/39

Aldehydes and Ketones:

Nucleophilic Addition to the

Carbonyl Group


2/39


3/39

Longest chain that contains the aldehyde group is the parent

chain. Aldehyde C is C-1.

Nomenclature

4,4-Dimethylpentanal 5-Hexenal or Hex-5-enal 2-Phenylbutanedial


4/39

Nomenclature

Cyclopentanecarbaldehyde2-Naphthalenecarbaldehyde

or Naphthalene-2-carbaldehyde

When a formyl group (CH=O) is attached to a ring, the ringname is followed by the suffix -carbaldehyde.


5/39

Acceptable common names.

Nomenclature

Formaldehyde

(methanal)

Acetaldehyde

(ethanal)

Benzaldehyde

(benzenecarbaldehyde)


6/39

Nomenclature

With oxygen-containing groups a higher oxidation state

substituent takes precedence so the –OH is a hydroxy

substituent.

5-Hydroxypentanal

trans-4-Hydroxycyclohexanecarbaldehyde

p-Hydroxybenzaldehyde


7/39

With ketones, the -e ending of an alkane is replaced by -one

in the longest continuous chain containing the carbonyl group.

The chain is numbered to give a lower number for this group.

Nomenclature

3-Hexanone

or Hexan-3-one

4-Methyl-2-pentanone

or 4-Methylpentan-2-one

4-Methylcyclohexanone


8/39

Ketone has preference over alcohols, halides, alkenes, and

alkyl groups in name and numbering.

Nomenclature

4-Methyl-3-penten-2-one

or 4-Methylpent-3-en-2-one

Aldehydes have preference over ketones in name and

numbering – ketone is an oxo substituent.

2-Methyl-4-oxopentanal


9/39

17.2

Structure and Bonding:The Carbonyl Group


10/39

The carbonyl is flat with sp2 hybridization of carbon and oxygen

with bond angles about 120o.

Structure and Bonding


11/39

Structure and Bonding

The C=O comprises a s-bond and a p-bond (shown) similar to

ethylene.


12/39

The carbonyl group makes aldehydes and ketones polar.

Carbonyl and Polarity

CH3CH2CH=CH21-Butene

Dipole moment: 0.3 D

CH3CH2CH=O

Propanal

Dipole moment: 2.5 D


13/39

Ways to show this polarization include.


Or using resonance structures.


14/39

Electrostatic potential maps show positive potential aspurple and negative potential as red.


1-Butene (CH3CH2CH=CH2) Propanal (CH3CH2CH=O)


15/39

The polarity and structure dictate the reactivity of carbonyls.

Structure, Bonding and Reactivity

electrophiles, especially

protons, bond to oxygen

nucleophiles

bond to carbon


16/39

Heats of combustion reveal that 2-butanone is more stablethan its aldehyde isomer butanal.

Structure and Stability

Butanal

2475 kJ/mol (592 kcal/mol)

2-Butanone

2442 kJ/mol (584 kcal/mol)

Heats of combustion


17/39

17.3

Physical Properties


18/39

Higher boiling points than alkanes and alkenes due to

stronger dipole-dipole forces. Lower boiling points thanalcohols which have stronger hydrogen bonding.

Physical Properties

Name

bp (1 atm)

Solubility in

water (g/100 mL)

1-Butene

-6°C

Negligible

Propanal

49°C

20

1-Propanol

97°C

Miscible in all

proportions

More water soluble than alkanes and alkenes since the

carbonyl can hydrogen bond to water but less than

alcohols.


19/39

17.4

Sources of Aldehydes and Ketones


20/39

Naturally Occurring Ketones and Aldehydes


21/39

Reactions that Form Ketones and Aldehydes


22/39

Reactions that Form Ketones and Aldehydes


23/39

Strategy. Reduction then oxidation.

Combinations of Reactions to Form Aldehydes

Example.


24/39

Strategy. Grignard reaction then oxidation.

Combinations of Reactions to Form Ketones

Example.


25/39

Formaldehyde, acetaldehyde and acetone can be prepared

by dehydration of an alcohol.

Industrial Syntheses

Hydroformylation of alkenes yields aldehydes.


26/39

17.5

Reactions of Aldehydes and Ketones:A Review and a Preview


27/39

Review of Reactions of Ketones and Aldehydes


28/39

A negatively polarized atom or group bonds to the positively

polarized carbon of the carbonyl group in the rate-

determining step of these reactions.

Nucleophilic Addition Reactions


29/39

17.6

Principles of Nucleophilic Addition:Hydration of Aldehydes and Ketones


30/39

Aldehydes and ketones react with water in a rapid equilibrium.

The product is a geminal diol, also called a hydrate.

An addition reaction.

Effects of Structure on Equilibrium


31/39



32/39

Electronic effect:

Alkyl substituents stabilize ketones more than aldehydes.



33/39

Electronic effect:Trifluoromethyl substituents are electron withdrawing and

therefore destabilize the carbonyl. Opposite effect to

alkyl substituents: hydrate favored!



34/39

Steric Effects:

Bond angles at C shrink from ≈120 in the reactant to ≈109.5o

in the hydrate. This introduces crowding and with more alkyl

groups Khydr decreases.



35/39

Mechanism of Hydration in Basic Solution

Step 1. Nucleophilic attack.

Reaction equation.

Step 2. Protonation.


36/39


Potential energy diagram for base catalyzed hydration.


37/39

Mechanism of Hydration in Acidic Solution

Step 1. Protonation.

Reaction equation.


38/39

Mechanism of Hydration in Acidic Solution

Step 2. Nucleophilic attack.

Step 3. Deprotonation.


39/39


Potential energy diagram for base catalyzed hydration.

Documents

Aldehyde Ketone 1