Problem 47 - A Complete Resource Book in Chemistry for JEE Main

Question

The IUPAC name of cinnamic acid is (a) phenylpropanoic acid (b) 3-phenylprop-2-enoic acid (c) 3-phenylpropanoic acid (d) benzene-1, 4 -dicarboxylic acid

Step-by-Step Solution

Answer

The IUPAC name of cinnamic acid is 3-phenylprop-2-enoic acid.

Step 1: Identify the Structure

Cinnamic acid is a carboxylic acid with the formula C9H8O2. Its structure consists of a phenyl group (C6H5-) attached to a propenoic acid group (CH=CHCOOH). The presence of the double bond between the second and third carbon atoms indicates that it's an unsaturated carboxylic acid.

Step 2: Determine the Parent Chain

For the IUPAC nomenclature, identify the longest carbon chain containing the carboxylic acid functional group. In cinnamic acid, this chain is a three-carbon chain (propionic acid) including the carboxylic acid (COOH) group and the adjacent carbon atoms.

Step 3: Identify Functional Groups and Substituents

Cinnamic acid has a phenyl group attached to the main propionic acid chain. The double bond between second and third carbons distinguishes it as a 'prop-2-enoic acid' rather than a simple 'propanoic acid'. This describes the unsaturation (double bond) in the chain.

Step 4: Combine Parts for the IUPAC Name

Combine the terms to reflect the placement of the phenyl group and the unsaturation in the main carbon chain. This results in the name '3-phenylprop-2-enoic acid' where the phenyl is at position 3 and the double bond at position 2 to 3.

Key Concepts

Cinnamic Acid

Cinnamic acid is an organic compound that plays a significant role in the world of chemistry, especially in terms of nomenclature and structure. It consists of a phenyl ring linked to a propene chain, where the carboxylic acid group is positioned at the end. Its molecular formula is C9H8O2, reflecting the fusion of aromatic and aliphatic features. In this compound, the phenyl group is attached to a three-carbon alkenoic acid.
The notable feature of cinnamic acid is its unsaturated chain due to the presence of a carbon-carbon double bond. This double bond contributes to the reactivity and various chemical properties of the compound. Cinnamic acid is naturally found in several plants and is often used in flavorings, perfumes, and pharmaceuticals due to its aromatic characteristics.

Carboxylic Acids

Carboxylic acids are a group of organic compounds that contain a carboxyl group (-COOH). This functional group is crucial for the chemical behavior of carboxylic acids, making them acidic in nature. When dissolved in water, they can donate a proton (H+), resulting in a carboxylate ion.
Carboxylic acids are typically named by identifying the longest carbon chain that includes the carboxyl group. The name is derived by replacing the suffix '-ane' of the corresponding alkane with '-oic acid'. Their polarity and ability to form hydrogen bonds make them highly soluble in water, especially those with short carbon chains. However, as the carbon chain length increases, the solubility decreases.

• Formic acid (HCOOH), the simplest carboxylic acid
• Acetic acid (CH3COOH), well-known as vinegar
• Cinnamic acid, notable for its aromatic properties

These examples highlight the diversity within carboxylic acids.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons are organic molecules that contain at least one carbon-carbon double or triple bond. Cinnamic acid falls under this category with its distinctive double bond between two carbon atoms. The presence of these multiple bonds means unsaturated hydrocarbons can undergo addition reactions, contributing to their versatility in organic synthesis.
There are two main types of unsaturated hydrocarbons: alkenes, with one or more double bonds, and alkynes, with one or more triple bonds. These bonds improve reactivity compared to their saturated counterparts (alkanes), influencing both physical properties and chemical reactivity. In various chemical reactions, these compounds can sway the direction of synthesis due to their reactive double or triple bonds.

• Alkenes: Hydrocarbons with carbon-carbon double bonds, like ethene (C2H4)
• Alkynes: Hydrocarbons with carbon-carbon triple bonds, like acetylene (C2H2)

Unsaturated hydrocarbons serve as essential building blocks in the production of polymers, alcohols, and other key chemical products.