Chapter 10. Organic Chemistry

# 10.6 Nomenclature of Aldehydes, Ketones, Carboxylic Acids, Esters, and Amides

### Learning Objectives

By the end of this section, you will be able to:

• Describe the structure and properties of aldehydes, ketones, carboxylic acids, esters and amides
• Name and draw structures for aldehydes, ketones, carboxylic acids, esters and amides

Another class of organic molecules contains a carbon atom connected to an oxygen atom by a double bond, commonly called a carbonyl group. The carbonyl group can attach to two other substituents leading to several subfamilies, some of which are: aldehydes, ketones, carboxylic acids, esters and amides.

## Naming of Aldehydes and Ketones

Both aldehydes and ketones contain a carbonyl group. In an aldehyde, the carbonyl group is bonded to at least one hydrogen atom. In a ketone, the carbonyl group is bonded to two carbon atoms.  The names for aldehyde and ketone compounds are derived using similar nomenclature rules as for alkanes and alcohols, and include the class-identifying suffixes -al and -one, respectively:

Therefore when naming aldehydes following IUPAC, you follow these rules:

Rule 1. Identify the longest chain of carbons which contains the carbonyl group (PREFIX-ANE+AL).  And when numbering the parent chain, the carbonyl group gets the lowest possible number, therefore it is always 1 and therefore is not included in the name.

Rule 2. Names and position of the substituents.

Methanal has a common name with which you may be familiar: formaldehyde.

When naming ketones following IUPAC, you follow these rules:

Rule 1. Identify the longest chain of carbons which contains the carbonyl group (PREFIX-#-ANE+ONE).  And when numbering the parent chain, the carbonyl group gets the lowest possible number.  In the smaller ketones (propanone and butanone), the locant number is not used because there is no alternative placement in these smaller ketones.

Rule 2. Names and position of the substituents.

The common name for propanone is acetone. There is a non-IUPAC way to name ketones that is commonly used as well: name the alkyl groups that are attached to the carbonyl group and add the word ketone to the name. So propanone can also be called dimethyl ketone, while butan-2-one is called methyl ethyl ketone.

In condensed structure, an aldehyde group is represented as –CHO; a ketone is represented as –C(O)– or –CO–.

### Example 1

Draw the structures of:  a) pentan-2-one;   b) hexan-2-one;    c) butane

Solution

a) This molecule has five C atoms in a chain, with the carbonyl group on the second C atom. Its structure is:

b) This molecule has six C atoms in a chain, with the carbonyl group on the second C atom. Its structure is:

c) This molecule has four C atoms in a chain, with the carbonyl group on the first C atom since it is an aldehyde (ends with -al). Its structure is:

Test Yourself
Give the condensed structure of the following amines:

a) propanone   b) propanal   c) heptan-3-one   d) octanal

Answer

a) CH3COCH3    b) CH3CH2CHO

c) CH3CH2CH2CH2COCH2CH3   or  CH3(CH2)3COCH2CH3

d) CH3CH2CH2CH2CH2CH2CH2CHO   or  CH3(CH2)6CHO

## Naming Carboxylic Acids and Esters

Both carboxylic acids and esters contain a carbonyl group with a second oxygen atom bonded to the carbon atom in the carbonyl group by a single bond. In a carboxylic acid, the second oxygen atom also bonds to a hydrogen atom. In an ester, the second oxygen atom bonds to another carbon atom. The names for carboxylic acids and esters include prefixes that denote the lengths of the carbon chains in the molecules.

The names for carboxylic acid and ester compounds are derived using similar nomenclature rules as seen previously with aldehydes, and include the class-identifying suffixes -oic acid and -oate, respectively:

Therefore when naming carboxylic acids following IUPAC, you follow these rules:

Rule 1. Identify the longest chain of carbons which contains the carbonyl group (PREFIX-ANE+OIC ACID).  And when numbering the parent chain, the carbonyl group gets the lowest possible number, therefore it is always 1 and therefore is not included in the name.

Rule 2. Names and position of the substituents.

When naming esters following IUPAC, you follow these rules:

Rule 1. Identify the longest chain of carbons which contains the carbonyl group (PREFIX-ANE+OATE).  And when numbering the parent chain, the carbonyl group gets the lowest possible number, therefore it is always 1 and therefore is not included in the name.  AND then name the other carbon chain (PREFIX+YL).

Rule 2. Names and position of the substituents.

The functional groups for an acid and for an ester are shown in red in these formulas.  In brackets you have the common names for ethanoic acid and methyl ethanoate.

The hydrogen atom in the functional group of a carboxylic acid will react with a base to form an ionic salt:

Carboxylic acids are weak acids (see the chapter on acids and bases), meaning they are not 100% ionized in water. Generally only about 1% of the molecules of a carboxylic acid dissolved in water are ionized at any given time. The remaining molecules are undissociated in solution.

In condensed structure, the carboxylic acid group is represented as –COOH; an ester is represented as –COO– .

### Example 2

Draw the structures of:  a) 3-methylpentanoic acid;   b) ethyl ethanoate;    c) propyl 2-chlorobutanoate

Solution

a) Its structure is:

b)Its structure is:

c) Its structure is:

Test Yourself
Name the following compounds:

a) CH3CH2COOH  b) CH3CH2CH2CH2COOCH2CH3  c) BrCH2(CH2)2COCH3  d) (CH3)2CH(CH2)6COOH

Answer

a) propanoic acid   b) ethyl pentanoate   c) methyl 4-bromobutanoate    d) 9-methylnonanoic acid

### Example 3

Complete the chemical reaction.

Solution

The OH ion removes the H atom that is part of the carboxyl group:

The carboxylate ion, which has the condensed structural formula CH3CO2, is the ethanoate ion, but it is commonly called the acetate ion.

Test Yourself

Complete the chemical reaction.

Answer

The ion is the methanoate ion, which is commonly called the formate ion.

## Naming Simple Amides

Amides are molecules that contain nitrogen atoms connected to the carbon atom of a carbonyl group.  The names for amide compounds are derived using similar nomenclature rules as seen previously with aldehydes and carboxylic acids, and include the class-identifying suffixes -amide:

Therefore when naming amides following IUPAC, you follow these rules:

Rule 1. Identify the longest chain of carbons which contains the carbonyl group (PREFIX-ANE+AMIDE).  And when numbering the parent chain, the carbonyl group gets the lowest possible number, therefore it is always 1 and therefore is not included in the name.

Rule 2. Names and position of the substituents.

In condensed structure, the amide group is represented as –CONHor –CONHR or –CONR2.

### Example 4

Give the condensed structures of:  a) decanamide;   b) hexanamide;    c) 2-chloroethanamide

Solution

a) Its condensed structure is: CH3(CH2)8CONH2

b) Its condensed structure is: CH3(CH2)4CONH2

c) Its condensed structure is: ClCH2CONH2

Test Yourself
Name the following compounds:

a) CH3(CH2)2CONH2  b) BrCH2(CH2)3CONH2  d) (CH3CH2)2CH(CH2)5CONH2

Answer

a) butanamide  b) 5-bromopentanamide   c) 7-ethylnonanamide

## Key Concepts and Summary

Functional groups related to the carbonyl group include the –CHO group of an aldehyde, the –CO– group of a ketone, the –CO2H group of a carboxylic acid, the –CO2R group of an ester and the –CONHgroup of an amide.

The systematic methods of naming these carbonyl containing functional groups follow a similar procedure and the names have three main parts:

1) specifying the information about the substituents,

2) specifying the information about the parent chain, and

3) the ending which specifies what functional group is present in the structure being named.

Aldehydes:    #-substituentsPREFIXANE+AL

Ketones:   #-substituentsPREFIXANE+ONE

Carboxylic Acids:   #-substituentsPREFIXANE+OIC ACID

Esters:   ALKYL #-substituentsPREFIXANE+OATE

Amides:   #-substituentsPREFIXANE+AMIDE

### Exercises

1. Write a condensed structural formula of the following compounds.

a) 2-propanol

b) acetone

c) dimethyl ether

d) acetic acid

e) 3-methyl-1-hexene

2. A peptide is a short chain of amino acids connected by amide bonds. How many amide bonds are present in this peptide?

3. How many amide bonds are present in this peptide? (See Exercise 2 for the definition of a peptide.)

4. Name a similarity between the functional groups found in aldehydes and ketones. Can you name a difference between them?

5. Name each molecule.

a)       b)

6. Name each molecule.

a)      b)

7. Name each molecule.

a)      b)

8. Name each molecule.

a)      b)

9. Name this molecule.

10. The drug known as aspirin is shown here.  Identify the functional group(s) in this molecule.

11. The drug known as naproxen sodium is the sodium salt of the molecule shown here. Identify the functional group(s) in this molecule.

Answers
1. a) CH3CH(OH)CH3
b) $\text{CH}_3\text{COCH}_3$:
c) CH3OCH3
d) CH3COOH
e) CH3CH2CH2CH(CH3)CHCH2
2. two amide bonds
3. one amide bond

4. They both have a carbonyl group, but an aldehyde has the carbonyl group at the end of a carbon chain, and a ketone’s carbonyl carbon is surrounded by two other carbons.

5. a)  proposal b)  butanone

6. a) 3-chloro-3-methylbutanal  b) heptan-4-one

7. a)  3-methylbutanoic acid      b)  ethyl propionate

8. a) 2,2,2-trichlroethanoic acid    b) butyl ethanoate

9. ethyl propyl ether

10. carboxylic acid, arene and ester

11. carboxylic acid, arene and ether

## Glossary

aldehyde: organic compound containing a carbonyl group bonded to two hydrogen atoms or a hydrogen atom and a carbon substituent

carbonyl group: carbon atom double bonded to an oxygen atom

carboxylic acid: organic compound containing a carbonyl group with an attached hydroxyl group

ester: organic compound containing a carbonyl group with an attached oxygen atom that is bonded to a carbon substituent

ketone: organic compound containing a carbonyl group with two carbon substituents attached to it

## License

CHEM 1114 - Introduction to Chemistry by Shirley Wacowich-Sgarbi is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.