CHAPTER 13: Unit 2. Nomenclature

Learning Objectives

1. Identify the general structure for an aldehyde and a ketone.
2. Use common names to name aldehydes and ketones.
3. Use the IUPAC system to name aldehydes and ketones.

The IUPAC names of the aldehydes and ketones are based on the longest chain that contains carbonyl group. The chain numbering is done from the end results in the lower number for the carbonyl group. The names of the aldehydes end in -al , those of ketones in -one. Cyclic ketones are named by giving the name of the carbon ring and adding the suffic-one. Numbers and names of the ring substituents are appended always considering carbonyl carbon at number 1 position. Position of number 1 is not included in the name.

Nomenclature of Aldehyde:

1. Select as the parent carbon chain the longest chain that includes the carbon atom of the carbonyl group.
2. name the parent chain by changing the -e ending of the corresponding alkane name to -al.
3. Number the parent chain by assigning the number 1 to the carbonyl carbon atom of the aldehyde group. the number 1 however does not become part of the name.
4. determine the identity and location of any substituents and append this information to the front o fthe parent side chain.
5. When an aldehyde functional group is attached to a carbon ring, nam ethe ring and add the suffix-carbaldehyde.

Small unbranched aldehydes have common names:

methanal= formaldehyde

ethanal= Acetaldehyde

propanal= Propionaldehyde

butanal= butyraldehyde

In case of aromatic aldehydes in which an aldehyde group is attached to a benzene ring are named as derivatives of benzaldehyde.

                                                                                              benzaldehyde

Nomenclature for Ketone:

1. select as the parent carbon chain the longest carbon chain that includes the carbon atom of the carbonyl group.
2. Name the parent chain by changing -e ending of the corresponding alkane name to -one.
3. Number the carbon chain such that the carbonyl carbon atom receives the lowest possible number. The position of the carbonyl carbon atom is noted by placing a number immediately before the name of the parent chain.
4. determine the identity and location of any substituents, and append this information to the front of the parent carbon chain name.
5. Cyclic ketones are named by giving the name of the carbon ring and adding the suffix -one. Numbers and names for ring substituents are appended with the carbonyl carbon always being carbon 1. the “1” designating the carbonyl carbon atom location is not included in the name.

The procedure for common names for ketones is the same as that used for ether common names. They are constructed by giving alphabetical order, the names of the alkyl or aryl groups attached to the carbonyl functional group and then adding the word ketone. Unlike aldehydes, ketones have two three words.

Example

Draw the structure for each compound.

1. 7-chlorooctanal
2. 4-methyl–3-hexanone

Solution

1. The octan– part of the name tells us that the LCC has eight carbon atoms. There is a chlorine (Cl) atom on the seventh carbon atom; numbering from the carbonyl group and counting the carbonyl carbon atom as C1, we place the Cl atom on the seventh carbon atom.
2. The hexan– part of the name tells us that the LCC has six carbon atoms. The 3 means that the carbonyl carbon atom is C3 in this chain, and the 4 tells us that there is a methyl (CH₃) group at C4:

Homework Exercises

1. Name each compound.

a.

b.

c.

d.

2. Name each compound.

a.

b.                 CH₃CH₂CH₂CH₂CH₂CHO

c.

d.

3. Draw the structure for each compound.

a. butyraldehyde

b. 2-hexanone

c. p-nitrobenzaldehyde

4. Draw the structure for each compound.

a. 5-ethyloctanal

b. 2-chloropropanal

c. 2-hydroxy-3-pentanone

Answers

1.

a. propanal or propionaldehyde

b. butanal or butyraldehyde

c. 3-pentanone or diethyl ketone

d. benzaldehyde

3.

a.                  CH₃CH₂CH₂CHO

b.

c.