Alcohols to Carboxylic Acids

Now that you know the major functional groups, it is time to learn how they change the IUPAC name. Each functional group has a specific suffix (when it is the highest-priority group) and a specific prefix (when a higher-priority group takes the suffix instead). This section covers the first five of the most important compound classes: alcohols, ethers, aldehydes, ketones, and carboxylic acids.

Naming Alcohols (-OH)

Alcohols contain a hydroxyl group (-OH) attached to an sp3-hybridized carbon.

IUPAC suffix: “-ol”
IUPAC prefix (when not the principal group): “hydroxy-”

Steps:

1. Find the longest chain that includes the carbon bearing the -OH group
2. Change the “-e” at the end of the parent alkane to “-ol”
3. Number the chain so the -OH gets the lowest possible locant
4. Name and number any substituents as usual

Examples:

• Methanol: CH3OH. One carbon + -ol = methanol
• Ethanol: CH3CH2OH. Two carbons + -ol = ethanol
• Propan-2-ol: CH3CH(OH)CH3. Three carbons, -OH at carbon 2 = propan-2-ol (older format: 2-propanol)
• Butan-1-ol: CH3CH2CH2CH2OH. Four carbons, -OH at carbon 1 = butan-1-ol

Classification of alcohols:
Alcohols are classified by the carbon bearing the -OH:

• Primary (1°): -OH is on a carbon bonded to one other carbon (e.g., butan-1-ol)
• Secondary (2°): -OH is on a carbon bonded to two other carbons (e.g., propan-2-ol)
• Tertiary (3°): -OH is on a carbon bonded to three other carbons (e.g., 2-methylpropan-2-ol)

This classification directly affects reactivity. Primary alcohols can be oxidized to aldehydes and then to carboxylic acids. Secondary alcohols are oxidized to ketones. Tertiary alcohols resist oxidation. This pattern is heavily tested on the MCAT.

Naming Ethers (R-O-R’)

Ethers have an oxygen atom bonded to two carbon groups. They are relatively unreactive, which makes them excellent solvents.

Ethers are named in two ways:

Common naming (more common on the MCAT): Name the two alkyl groups on either side of the oxygen, alphabetically, followed by “ether.”

• Diethyl ether: CH3CH2-O-CH2CH3 (two ethyl groups)
• Methyl tert-butyl ether (MTBE): CH3-O-C(CH3)3

IUPAC naming: The smaller alkyl group + oxygen is treated as an “alkoxy” substituent on the longer chain.

• Methoxyethane: CH3-O-CH2CH3 (methoxy group on ethane)
• 2-methoxypropane: CH3-O-CH(CH3)2

The “alkoxy” names are formed by replacing “-yl” with “-oxy”: methyl becomes methoxy, ethyl becomes ethoxy, propyl becomes propoxy.

Naming Aldehydes (-CHO)

Aldehydes have a carbonyl group (C=O) at the terminal position of a chain. The carbonyl carbon is always carbon 1.

IUPAC suffix: “-al”
IUPAC prefix (when not the principal group): “oxo-” or “formyl-”

Steps:

1. Find the longest chain that includes the carbonyl carbon
2. Replace “-e” with “-al”
3. The carbonyl carbon is automatically carbon 1 (no locant needed for the -CHO group itself)
4. Name and number substituents

Examples:

• Methanal: HCHO. One carbon + -al = methanal (common name: formaldehyde)
• Ethanal: CH3CHO. Two carbons + -al = ethanal (common name: acetaldehyde)
• Propanal: CH3CH2CHO. Three carbons + -al = propanal
• 3-methylbutanal: (CH3)2CHCH2CHO. Four carbons + -al with methyl at C3 = 3-methylbutanal

Since the aldehyde carbon is always at the end of the chain (carbon 1), you never need to specify its position - the “-al” suffix already tells you it is terminal.

Naming Ketones (C=O, internal)

Ketones have a carbonyl group in the interior of the chain, bonded to two carbon groups.

IUPAC suffix: “-one”
IUPAC prefix (when not the principal group): “oxo-”

Steps:

1. Find the longest chain that includes the carbonyl carbon
2. Replace “-e” with “-one”
3. Number the chain so the carbonyl gets the lowest possible locant
4. Name and number substituents

Examples:

• Propan-2-one: CH3COCH3. Three carbons, carbonyl at C2 = propan-2-one (common name: acetone)
• Butan-2-one: CH3COCH2CH3. Four carbons, carbonyl at C2 = butan-2-one (common name: methyl ethyl ketone)
• Pentan-3-one: CH3CH2COCH2CH3. Five carbons, carbonyl at C3 = pentan-3-one

Naming Carboxylic Acids (-COOH)

Carboxylic acids have both a carbonyl (C=O) and a hydroxyl (-OH) on the same carbon, at the end of the chain. They are the highest-priority functional group in IUPAC naming.

IUPAC suffix: “-oic acid”
IUPAC prefix (when not the principal group): “carboxy-”

Steps:

1. Find the longest chain that includes the carboxyl carbon
2. Replace “-e” with “-oic acid”
3. The carboxyl carbon is automatically carbon 1
4. Name and number substituents

Examples:

• Methanoic acid: HCOOH. One carbon + -oic acid = methanoic acid (common name: formic acid)
• Ethanoic acid: CH3COOH. Two carbons + -oic acid = ethanoic acid (common name: acetic acid)
• Propanoic acid: CH3CH2COOH. Three carbons + -oic acid = propanoic acid
• 2-methylpropanoic acid: (CH3)2CHCOOH. Three carbons + -oic acid with methyl at C2 = 2-methylpropanoic acid

Like aldehydes, the carboxyl carbon is always at the terminal position, so no locant is needed for the -COOH group.

Dicarboxylic Acids

When a molecule has a -COOH group on both ends, it is a dicarboxylic acid. The suffix becomes “-dioic acid.”

Several of these common names appear in the Krebs cycle: succinic acid (succinate) and oxalic acid (oxalate) are Krebs cycle intermediates. The MCAT will use these common names in biochemistry passages.

Summary: Suffixes for This Section