Naming Carboxylic Acids: Videos & Practice Problems

Carboxylic acids are characterized by a carbonyl group (C=O) attached to a hydroxyl group (OH), making the carbon in the carbonyl group the number one carbon in naming conventions. When naming carboxylic acids, the 'e' at the end of the corresponding alkane name is replaced with 'oic acid'. It is essential to locate and name any substituents present, ensuring the parent chain reflects the carboxylic acid functional group. This nomenclature is crucial for the correct identification and classification of carboxylic acids in organic chemistry.

Rules for Naming Carboxylic Acids

Carboxylic acids are organic compounds characterized by the presence of a carbonyl group (C=O) directly bonded to a hydroxyl group (–OH). This functional group structure is essential for their classification and reactivity. When naming carboxylic acids, the rules are similar to those for aldehydes, with the carbonyl carbon always assigned as carbon number one in the chain.

The naming convention involves modifying the suffix of the corresponding alkane. Specifically, the 'e' at the end of the alkane name is replaced with 'oic acid' to indicate the presence of the carboxylic acid functional group. For example, the alkane "pentane" becomes "pentanoic acid" when it is converted into a carboxylic acid.

Additionally, it is important to indicate the positions of any substituents on the carbon chain. This ensures clarity in the structure of the compound. As you practice naming various carboxylic acids, remember to apply these conventions consistently to accurately reflect their chemical nature.

Naming Carboxylic Acids Example

To systematically name a carboxylic acid, follow these steps to ensure accuracy and clarity in the naming process. First, identify the longest carbon chain that includes the carboxylic acid group (–COOH), as this will serve as the parent chain. In cases where there are multiple chains of equal length, select the one with the most substituents.

Next, assign names to the substituents present on the carbon chain. For instance, if there is a bromine substituent, it is designated as "bromo," while a three-carbon alkyl group is referred to as "ethyl." Begin numbering the carbon chain from the carbon of the carboxylic acid group, which is considered carbon 1. Continue numbering sequentially along the chain.

After establishing the substituents and their positions, assign numerical locations to each substituent. It is important to list the substituents alphabetically, regardless of their numerical order. Use commas to separate numbers and dashes to separate letters from numbers. For example, if "bromo" appears before "ethyl" alphabetically, it will be listed first.

In this case, the bromo substituent is located on carbon 3, and the ethyl substituent is on carbon 4. Since the carbon of the carboxylic acid is carbon 1, it does not require a number designation. The longest carbon chain identified is six carbons long, which corresponds to "hexane." However, since it is a carboxylic acid, the name is modified to "hexanoic acid," changing the "e" ending to "oic acid."

Thus, the complete systematic name for the carboxylic acid is 3-bromo-4-ethylhexanoic acid.

If the substituent name of the OH group is hydroxy in the presence of a carboxylic acid, provide the systematic name for the following compound.

• A. 5-ethyl-4-hydroxyoctanoic acid
• B. 4-ethyl-5-hydroxyoctanoic acid
• C. 5- isopropyl-4-hydroxyoctanoic acid
• D. 4-isopropyl-5-hydroxyoctanoic acid

Answer: (B)

Here’s what students ask on this topic:

How do you name a carboxylic acid?

To name a carboxylic acid using the IUPAC system, follow these steps:

1. Identify the longest carbon chain that includes the carboxyl group (-COOH). The number of carbon atoms in this chain determines the base name of the acid.
2. Number the carbon atoms starting from the end nearest to the carboxyl group, which always receives the number 1.
3. Replace the '-e' ending of the corresponding alkane name with '-oic acid' to denote the presence of the carboxyl group. For example, a one-carbon chain is methane, so the carboxylic acid is methanoic acid (commonly known as formic acid).
4. If there are substituents (other groups or atoms attached to the main chain), name them and give their position numbers based on the numbering of the carbon chain. Prefix the substituent names to the front of the carboxylic acid name.
5. If there is more than one carboxyl group, use the suffixes '-dioic acid', '-trioic acid', etc., and number each carboxyl group.

For example, a four-carbon chain with a carboxyl group at the end is butanoic acid. If there is a chlorine substituent on the second carbon, it becomes 2-chlorobutanoic acid.

How is the name of a carboxylic acid derived from the corresponding alkane?

The name of a carboxylic acid is derived from the corresponding alkane by changing the '-ane' suffix to '-anoic acid.' Here's the step-by-step process:

1. Identify the longest carbon chain that includes the carboxyl group (COOH). This chain determines the base name of the alkane.
2. Number the carbon atoms in the chain starting from the end nearest to the carboxyl group, ensuring that this group has the lowest possible number (which will be 1, as the carboxyl group must be at the end of the chain).
3. Replace the '-ane' suffix of the alkane with '-anoic acid' to indicate the presence of the carboxyl group. For example, if the longest chain has four carbons and is butane, the corresponding carboxylic acid is butanoic acid.
4. If there are substituents or branches on the carbon chain, indicate their position using the appropriate numbers and names before the base name of the acid.

Remember that the carboxyl group has the highest priority, so it defines the numbering of the carbon chain and the resulting name of the acid.

What is the IUPAC name for carboxylic acid?

The IUPAC (International Union of Pure and Applied Chemistry) name for a carboxylic acid is derived from a systematic approach to naming organic compounds. The general formula for a carboxylic acid is $R-\mathrm{COOH}$, where R represents the hydrocarbon part of the molecule. To name a carboxylic acid using IUPAC rules, you follow these steps:

1. Identify the longest carbon chain that contains the carboxyl group (COOH). This chain determines the base name of the acid.
2. Number the carbon atoms in the chain starting from the end nearest the carboxyl group, which always receives the number 1.
3. Replace the 'e' at the end of the alkane name (corresponding to the carbon chain length) with the suffix 'oic acid'. For example, a one-carbon chain with a carboxyl group is called methanoic acid (common name: formic acid), and a two-carbon chain is called ethanoic acid (common name: acetic acid).
4. If there are substituents or branches on the carbon chain, their positions are indicated by the appropriate numbers, and their names are prefixed to the base name.

Remember, the carboxyl group has the highest priority when numbering the carbon chain in IUPAC nomenclature for carboxylic acids.

How do you name a carboxylic acid as a substituent?

When a carboxylic acid group is a substituent on a larger molecule, it is named using the prefix "carboxy-" followed by the name of the parent hydrocarbon chain. The carbon of the carboxylic acid group is not included in the numbering of the parent chain; instead, it is considered as a substituent.

For example, if you have a benzene ring with a carboxylic acid group attached, the compound would be named as "carboxybenzene." If the parent chain is a longer alkane, you would name the compound by identifying the number of the carbon to which the carboxylic acid is attached, followed by the prefix "carboxy-" and the name of the alkane. For instance, if a carboxylic acid group is attached to the third carbon of a pentane chain, it would be named "3-carboxypentane."

Remember that the carboxylic acid group has priority in the naming process, so it often dictates the numbering of the carbon atoms in the parent chain to give it the lowest possible number.