Functional Groups with the C = O Bond

Functional Groups with the C = O Bond

Aldehydes, Ketones, Carboxylic Acids, Esters and Amides

The Carbonyl Group

• Functional group where a carbon atom is double-bonded to an oxygen atom

• Is this functional group likely to result in polar or non-polar molecules?

Aldehydes and Ketones

• Both have a carbonyl functional group• Aldehydes – the carbonyl group attached to

an end carbon.

• Ketones – the carbonyl group attached to an interior carbon.

Naming an Aldehyde

1. Name the parent alkane. The carbon of the carbonyl group is position 1.

2. Replace the “-e” with the suffix –al.3. Name side chains using regular IUPAC rules.

Note: No position number is needed for the carbonyl group (always #1)

Examples of Naming Aldehydes

• Name the following aldehydes:

Methanal (formaldehyde)

Butanal

Naming Ketones

1. Name the parent alkane. Main chain must contain carbonyl group.

2. Replace “-e” with the suffix “-one”. If more than 1 carbonyl, use -dione, -trione, etc.

3. If more than 4 carbons (main chain) a position number is needed for the carbonyl group.

4. Name side chains according to IUPAC rules.

Examples for Naming Ketones

• Name the following: OCH3

O

CH3 CH3

3-hexanone 3-propyl-2,6-octadione

Physical Properties• The C=O bond is polar, so aldehydes and

ketones are usually polar• H-bonds not possible b/n these molecules, but

they can be formed with water• With low molecular masses – very soluble in

water• Boiling points

Compound Boiling Point

propane 42.1 °C

1-propanol 97.4 °C

propanal 48.8 °C

Other characteristics

Aldehydes• Strong, pungent smell• Long chains used in

perfume• Polar solvents• Can be solvents for non-

polar compounds

Ketones• Sweet smell• Used in perfumes• Smell of roses is due to

ketones• Polar solvents• Can be solvents for non-

polar compounds

Carboxylic Acids• Organic compounds with the functional group,

-COOH in a complete structural diagram it looks like,

• Naming carboxylic acids1.Name the parent alkane.2.Replace the “-e” with “–oic acid”. The carbon

with the carbonyl group is number 1.3.Name and number the branches as usual.

Examples of carboxylic acids

• Name the following:

Drawing Carboxylic Acids

• Draw the following:a)4-ethyl-2,3-dimethylhexanoic acid

b)propenoic acid

c) 3-methylbenzoic acid

O

OH

CH2

O

OHCH3

O

OH

CH3

CH3

CH3

CH3

Properties of Carboxylic Acids

• Polar compounds• Due to hydroxyl (-OH) group, form two H-

bonds with each other and water• Low molecular weight compounds are

miscible with water• Solubility decreases as size increases• Very high boiling and melting points due to H-

bonds

Additional Characteristics of Carboxylic Acids

• Often have unpleasant odours (butanoic acid – rancid butter)

• In water, the H from the –OH group dissociates, so they behave like acids– This happens because the 2 O atoms can

accommodate the free electron (they are very electronegative)

Relative boiling points

• Rank in order from highest to lowest

CH3

CH3

CH3

OH

O

CH3

CH3

O

OH

CH3

Carboxylic Acid Derivatives

• The hydroxyl group is exchanged• Esters• Have the general formula RCOOR’• Formed by the following dehydration

reaction:

carboxylic acid + alcohol ester + water

Parts of an ester

• Esters are split into 2 parts– The parent acid, contains the C=O– The alkyl group

Naming Esters

1. Identify the parent acid. Name the parent acid.

2. Replace the “–oic acid” part of the name with “-oate”.

3. Name the alkyl part of the molecule like any other alkyl group.

4. Put 2 names together. The alkyl group and parent acid remain separate words.

Examples

• Name the following:

• CH3CH2CH2COOCH2CH3

• CH3CH2CH2CH2CH2CH2COOCH2CH3

• HCOOCH2CH3

O

O CH3

CH3methyl propanoate

Properties of Esters

• Polar molecules• No O-H bond, so can’t form H-bond with other

esters• Can form H-bonds with water• If molecular weight is low

– Soluble in water– Longer than 4 carbons = not soluble

• Low boiling points due to lack of H-bonds

Other Properties

• Many have pleasant smells and tastes– Used in perfumes and artificial flavours– Taste and smell of many fruits comes from esters

Amides

• Combination of a carboxylic acid and an amine.

• General formula: R – CO – NR2

– R can be a H atom or an alkyl group

Naming Amides

1. Name the carboxylic acid part of the molecule (contains C=O).

2. Drop the “oic acid” with the suffix “-amide”. The C=O carbon is position 1.

3. Name the alkyl groups attached to the N in alphabetical order. Use the letter “N” to indicate position. If there are identical groups use N,N-

4. Write the prefix, root and suffix together

Name the following

N – ethyl – N – methylbutamide N,N – diethylbutamide

Types of Amides

• Primary – only H attached to the N, no alkyl groups

• Secondary – 1 alkyl group attached to the N

• Tertiary – 2 alkyl groups attached to the N

Physical Properties of Amides

• C-N and N-H bonds are polar• Properties are similar to carboxylic acids• Primary amides have 2 N-H bonds, therefore

they have even more H-bonding than carboxylic acids...very high boiling points

• Amides are soluble in water. This decreases as size increases.