Problem 131 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following are incorrect statements? (a) IUPAC names of succinic acid is ethane 1, 2-dicarbolxylic acid. (b) Enantiomorphs possess identical biological properties. (c) Tetrahydrofuran is a heteroaromatic compound (d) Generally homologues are not isomers.

Step-by-Step Solution

Answer

Statements (b) and (c) are incorrect.

Step 1: Evaluate Statement (a)

Statement (a) claims that the IUPAC name of succinic acid is ethane 1,2-dicarboxylic acid. Review the structure of succinic acid, which is \( \text{C}_4\text{H}_6\text{O}_4 \), and consists of two carboxyl groups \( (-COOH) \) attached to a two-carbon alkane. Thus, the IUPAC name is correctly ethane-1,2-dicarboxylic acid. Statement (a) is correct.

Step 2: Evaluate Statement (b)

Statement (b) posits that enantiomorphs possess identical biological properties. Enantiomorphs, or enantiomers, are stereoisomers that are non-superimposable mirror images of each other. While they have identical physical properties, they can have different biological activity because biological molecules are often chiral. Therefore, the statement is incorrect.

Step 3: Evaluate Statement (c)

Statement (c) states that tetrahydrofuran is a heteroaromatic compound. Tetrahydrofuran (THF) is a five-membered ring containing four carbon atoms and one oxygen atom, but it lacks the necessary conjugated double-bond system to be considered aromatic. Instead, it is a heterocyclic, non-aromatic compound. This means Statement (c) is incorrect.

Step 4: Evaluate Statement (d)

Statement (d) claims that generally homologues are not isomers. In organic chemistry, homologues refer to a series of compounds that differ only by a repeating unit, such as CH2 in alkanes, and are typically not considered isomers since they have different molecular formulas. Hence, Statement (d) is correct.

Key Concepts

IUPAC Nomenclature

Understanding the IUPAC nomenclature system helps us name organic compounds systematically. It ensures that each compound has a unique and descriptive name. The IUPAC rules for naming are structured:

• Identify the longest carbon chain in the molecule, known as the parent chain.
• Number the carbon atoms in the parent chain starting from the end closest to any substituent group.
• Name and number any substituent groups attached to the parent chain.
• Combine these elements into a single name, starting with the substituents and ending with the parent chain.

For example, succinic acid (\(\text{C}_4\text{H}_6\text{O}_4 \)), which is correctly named ethane-1,2-dicarboxylic acid under IUPAC. This highlights that it has two carboxylic acid groups, making it a dicarboxylic acid. Hence, precision is crucial in this naming process.

Stereoisomers

Stereoisomers are fascinating because they have the same molecular formula and the same bond connectivity but differ in the spatial arrangement of atoms. This property makes them unique, as even small differences can lead to significant changes in properties. A key group of stereoisomers is called enantiomers or enantiomorphs. These are non-superimposable mirror images of each other, much like left and right hands. Despite having the same boiling point, melting point, and density, enantiomers can differ dramatically in behavior when interacting with other chiral substances, such as biological molecules. This specificity is why one enantiomer of a drug may be therapeutically active, while its counterpart could be inactive or even harmful. Therefore, understanding stereoisomers is crucial, especially in fields like pharmaceuticals.

Heterocyclic Compounds

Heterocyclic compounds are a class of organic compounds that feature rings containing atoms of at least two different elements. Carbon is typically one of these elements, with the other often being nitrogen, oxygen, or sulfur. Tetrahydrofuran (THF) is a classic example, consisting of a five-membered ring with one oxygen atom. Unlike aromatic heterocycles, such as pyridine, THF is non-aromatic. This is because it does not possess a conjugated system of double bonds required for aromatic stability. Nonetheless, THF is still highly significant in organic chemistry, functioning as a common solvent due to its good solvating properties and relatively low reactivity. This highlights the diversity and intricate behavior of heterocyclic compounds.

Homologous Series

In organic chemistry, a homologous series is a group of compounds exhibiting a regular pattern. These compounds differ by a constant unit, usually a -\(\text{CH}_2\)- group, making the series predictable and easy to understand.Examples include alkanes, alkenes, and alkynes, which share similar chemical properties and gradually changing physical properties with increasing molecular mass. Importantly, members of a homologous series are not isomers of each other, since isomers have the same molecular formula. Instead, they have a general formula that underlies the entire series, such as \[\text{C}_n\text{H}_{2n+2}\] for alkanes.Understanding homologous series helps chemists predict the behaviors of unknown compounds based on known relatives. This predictability makes them a powerful tool in the study and application of organic chemistry.