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, (c) 2-chloro-3-methyldecanoic acid.

Short answer

The structures of the given carboxylic acids are as follows: (a) Methanoic acid: HCOOH H | C=O | O-H (b) Pentanoic acid: CH3(CH2)3COOH CH3-CH2-CH2-CH2-C=O | O-H (c) 2-chloro-3-methyldecanoic acid: CH3(CH2)7CHClCH(CH3)COOH CH3-CH2-CH2-CH2-CH2-CH2-CH2-CHCl-CH(CH3)-C=O | O-H

Step-by-step solution

(a) Drawing the structure of methanoic acid)

Methanoic acid has only one carbon atom, as the prefix "meth" indicates. In a carboxylic acid, the carbon atom is bonded to an oxygen atom in a double bond, and an OH group. So, the structure of methanoic acid (HCOOH) is as follows: H | C=O | O-H

(b) Drawing the structure of pentanoic acid)

Pentanoic acid has five carbon atoms, as indicated by the prefix "pent." First, draw the linear carbon chain with five carbon atoms, and add the carboxylic acid functional group (C=O and an OH group) at one end. The structure of pentanoic acid (CH3(CH2)3COOH) is as follows: CH3-CH2-CH2-CH2-C=O | O-H

(c) Drawing the structure of 2-chloro-3-methyldecanoic acid)

2-chloro-3-methyldecanoic acid has a decyl (10 carbon atom) chain as its base structure, with a carboxylic acid functional group at one end, a chlorine atom at position 2 and a methyl group (CH3) at position 3. Draw the base chain, add the carboxylic acid functional group at one end, and add the chloro and methyl substituents at positions 2 and 3. The structure of 2-chloro-3-methyldecanoic acid (CH3(CH2)7CHClCH(CH3)COOH) is as follows: CH3-CH2-CH2-CH2-CH2-CH2-CH2-CHCl-CH(CH3)-C=O | O-H

Key concepts

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) has created a systematic way to name organic compounds to ensure that each name is unique and informative. This is important in organic chemistry, where many compounds can have similar structures and names. When naming carboxylic acids using IUPAC nomenclature, the core approach is to determine the longest continuous chain of carbon atoms including the carboxyl group (\(-COOH \)).

• The hydrocarbon chain is named based on the number of carbon atoms it contains. For example, a single carbon is "meth," while a chain with five is "pent."
• The suffix "-oic acid" replaces the final "e" in the parent alkane, indicating the presence of a carboxylic acid group. For example, "methane" becomes "methanoic acid."
• Substituents such as halogens or alkyl groups are prefixed to the name with their position numbers, highlighting the exact carbon atom to which they are attached.

By following these rules, one can consistently derive the IUPAC name for different carboxylic acids, ensuring clarity and universal understanding.

Molecular Structure

Understanding the molecular structure of carboxylic acids is essential for appreciating their properties and reactivity. Each carboxylic acid consists of a carboxyl group (\(-COOH \)), which uniquely defines its acidic characteristics. The carboxyl group is made up of a carbon atom that is doubly bonded to an oxygen atom (forming a carbonyl group) and singly bonded to a hydroxyl group (\(OH \)).

• In methanoic acid, there is only one carbon atom. This means it is the simplest carboxylic acid, with its structural formula being \(HCOOH \).
• Pentanoic acid has a longer carbon chain, with five carbon atoms. Its structure extends from \(CH_3\) to \(CH_2\) segments before ending in the \(COOH\) group.
• Complex carboxylic acids like 2-chloro-3-methyldecanoic acid include additional substituents and branching that must be considered when drawing their structures. These elements are placed at specific positions along the carbon chain, affecting the compound's overall reactivity and properties.

Drawing these structures helps visualize the spatial arrangement of atoms, thereby providing insights into the behavior of these acids in chemical reactions.

Organic Chemistry

Carboxylic acids form a crucial class of compounds in organic chemistry. They are characterized by their functional group, \(-COOH \), one of the most versatile groups that participate in various chemical reactions. Here are key aspects of carboxylic acids in organic chemistry:

• Reactivity: Carboxylic acids can undergo transformations into esters, amides, and other derivatives, making them invaluable in synthetic chemistry.
• Acidity: These acids can donate a proton (\(H^+\)), making them acidic. Their acidic nature is a result of the resonance stabilization of the carboxylate ion when the proton is lost.
• Natural Occurrence: Many carboxylic acids are found in nature, playing essential roles in metabolism and other biological processes. For instance, formic acid (methanoic acid) is found in ant venom.

Understanding carboxylic acids' role in organic chemistry is fundamental for students and researchers alike, as it opens the door to exploring numerous synthetic pathways and biochemical mechanisms.