Question

The IUPAC name for a carboxylic acid is based on the name of the hydrocarbon with the same number of carbon atoms. The ending -oic is appended, as in ethanoic acid, which is the IUPAC name for acetic acid. Draw the structure of the following acids: (a) methanoic acid. (b) pentanoic acid, and (c) 2 -chloro-3-methyldecanoic acid

Short answer

The structures of the three carboxylic acids are as follows: (a) Methanoic acid: HCOOH (b) Pentanoic acid: CH₃(CH₂)₃COOH (c) 2-chloro-3-methyldecanoic acid: CH₃(CH₂)CH(Cl)CH(CH₃)(CH₂)₅COOH

Step-by-step solution

Understand the IUPAC naming system for carboxylic acids

The IUPAC (International Union of Pure and Applied Chemistry) naming system for carboxylic acids is based on the name of the hydrocarbon with the same number of carbon atoms. The ending "-oic" is added, indicating the presence of a carboxyl group (-COOH) connected to the hydrocarbon chain.

Draw the structure of methanoic acid

Methanoic acid has only one carbon atom in its hydrocarbon chain. To draw the structure, connect the carboxyl group (-COOH) to the carbon atom, and fill the remaining bonds with hydrogen atoms. The structure is: HCOOH

Draw the structure of pentanoic acid

Pentanoic acid has a hydrocarbon chain containing five carbon atoms. Begin by drawing a straight chain of five carbon atoms (in a zigzag line), then add the carboxyl group (-COOH) to one end of the chain, and fill the remaining bonds with hydrogen atoms. The structure is: CH₃(CH₂)₃COOH

Draw the structure of 2-chloro-3-methyldecanoic acid

2-chloro-3-methyldecanoic acid has a hydrocarbon chain containing ten carbon atoms, a chlorine atom attached to the second carbon, and a methyl group (CH₃) attached to the third carbon. Begin by drawing a straight chain of ten carbon atoms (in a zigzag line). Next, add the carboxyl group (-COOH) to one end of the chain. Then, add the chlorine atom and methyl group to the appropriate carbon atoms (2-chloro and 3-methyl). Finally, fill the remaining bonds with hydrogen atoms. The structure is: CH₃(CH₂)CH(Cl)CH(CH₃)(CH₂)₅COOH

Key concepts

Hydrocarbon Chain

The backbone of organic chemistry, hydrocarbon chains, form the fundamental framework for carboxylic acids. Hydrocarbons are composed of carbon and hydrogen atoms joined together in a chain. The length and structure of this chain vary, determining the compound's properties.

In the context of carboxylic acids, these chains are linked to a carboxyl group. For instance, in pentanoic acid, a five-carbon hydrocarbon chain is bound to the carboxyl group, giving the molecule its characteristic features. Regardless of the length, all hydrocarbon chains in carboxylic acids terminate in a carboxyl group, which is responsible for their acidic nature and reactions. Understanding the arrangement of these chains is crucial for drawing the structural formula of carboxylic acids and for their accurate IUPAC naming.

Carboxyl Group

The carboxyl group, denoted as -COOH, is the defining functional group of carboxylic acids. It consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (-OH). This group is the source of the acidic properties of carboxylic acids.

When a carboxyl group is attached to the end of a hydrocarbon chain, it forms a carboxylic acid. For example, the simple carboxylic acid, methanoic acid, consists of a single carbon atom bonded to the -COOH group. In naming carboxylic acids, the presence of this carboxyl group is indicated by the suffix '-oic acid' appended to the name of the hydrocarbon from which it is derived.

Structural Formula of Carboxylic Acids

The structural formula of carboxylic acids is a graphical representation that shows the molecular arrangement, with the carboxyl group always located at one end of the hydrocarbon chain. Understanding how to draw these structures is vital for visualizing how atoms are connected in a molecule.

Take pentanoic acid, for instance. Its structural formula begins with a chain of five carbon atoms, linked end-to-end in a zigzag formation due to the tetrahedral nature of carbon's bonding. The carboxyl group bonds to the terminal carbon atom, and hydrogen atoms fill up the remaining valences. When additional substituents such as chlorine or methyl groups are present, they are added to the hydrocarbon chain at the indicated carbon numbers, which is critical for more complex structures like 2-chloro-3-methyldecanoic acid.

IUPAC Naming Rules

The International Union of Pure and Applied Chemistry (IUPAC) established rules for naming organic compounds, ensuring consistency and clarity. The naming of carboxylic acids follows a systematic approach: first, identify the length of the hydrocarbon chain; second, locate and name any substituents; and third, end the name with the suffix '-oic acid'.

Using these rules, 'methanoic acid' reflects a single-carbon carboxylic acid, while 'pentanoic acid' signals a five-carbon chain. For naming substituted carboxylic acids, numbers indicate the position of the substituents on the chain. For example, '2-chloro-3-methyldecanoic acid' describes a ten-carbon acid with a chloro group on the second carbon and a methyl group on the third. These crucial naming conventions facilitate accurate communication among chemists and are essential for students to master.