Chapter 16: Aldehydes and Ketones

Ochem

Functional group:

Aldehyde: C=O at the end of the chain →

Ketone: C=O in the middle of the chain →

Many have distinct smells (fruity, floral, etc.).

Most simple aldehydes and ketones are liquids.

• Carbonyl (C=O)

• R–CHO

• R–CO–R′

Physical properties of aldehydes and ketones

• What physical state are most simple aldehydes and ketones at room temperature?

• What causes aldehydes and ketones to have relatively high boiling points compared to alkanes?

• Why do aldehydes and ketones have lower boiling points than alcohols?

• They are liquids

• The polar carbonyl group (C=O) creates dipole–dipole interactions between molecules

• They cannot form hydrogen bonds with each other (no –OH group)

Physical properties of aldehydes and ketones

• Are small aldehydes and ketones soluble in water?

• What happens to water solubility as the carbon chain length increases?

• Do aldehydes and ketones have distinct smells?

• weak or strong acids?

• Yes, because they can hydrogen bond with water molecules.

• Solubility decreases because the nonpolar chain gets larger

• Yes — many have pleasant or noticeable odors, like fruity or floral scents

• weak 

Aldehydes IUPAC:

• Find the longest chain including the ?

• Carbonyl carbon is ?.

• Replace -e with ? → e.g., ethane → ?.

• If attached to a ring, use ?.

• If there’s more than one –CHO, use ?

Common names: Use acid name + ?

• –CHO group

• C1

• -al, ethanal

• –carbaldehyde

• Greek prefixes (di-, tri-) and keep the “-e.”

“aldehyde” (e.g., formaldehyde, acetaldehyde).

Problems 

1. Name the following compound:

2. Draw p-bromobenzaldehyde:

practice

Ketones IUPAC:

• Find the longest chain with the ?.

• Replace -e with ?→ e.g., propane → ?.

• Number so the carbonyl gets the lowest number.

Common names: Name the two alkyl groups alphabetically + ? (e.g., methyl ethyl ketone).

• carbonyl 

• -one, propan-2-one

“ketone”

Problems 

1. Name the following compounds:

2. Draw 2, 3-butanedione.

practice

More than a Ketone?

When an aldehyde or a ketone is a substituent, it is named as ?

an “oxo-” group

Preparation

• Aldehydes: 

• Ketones: 

• Oxidation of primary alcohols

• Oxidation of secondary alcohols

Tests

• Dichromate Test: ?

• Tollens’ Test:? 

• Aldehydes turn orange → green (positive). Ketones don’t react.

• Aldehydes form a silver mirror. Ketones give no reaction.

Reactions

Reduction:

• Aldehydes → ?

• Ketones → ?

• Reagents: ?

• 1° alcohols

• 2° alcohols 

• H₂/Pd, NaBH₄, LAH

Problems

practice

Reactions

Hemiacetal and Acetal Formation:

Aldehyde + alcohol → hemiacetal → acetal (with excess alcohol)

• hemiacetal: 1C is bonded to ?

• acetal: 1C is bonded to ?

• 1 OH group & 1 OR group 

• 2 OR groups

Problems 

Draw the missing reactant or product for the following reactions:

practice 

Reactions

Acetal Hydrolysis: Reverse reaction —?

acetal → aldehyde or ketone + alcohol

Problems

practice