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 (a), (b), and (c) are incorrect. Statement (d) is correct.

Step 1: Understanding Succine Acid

Succinic acid is a dicarboxylic acid with the formula \ \((CH_2)_2(COOH)_2\ \). Its IUPAC name is Butanedioic acid, not Ethane 1,2-dicarboxylic acid. Therefore, statement (a) is incorrect.

Step 2: Analyzing Enantiomorphs

Enantiomorphs, or enantiomers, are mirror-image isomers that do not possess identical biological properties. They often have different effects in biological systems. Thus, statement (b) is also incorrect.

Step 3: Evaluating Tetrahydrofuran

Tetrahydrofuran (THF) is a five-membered ring containing four carbon atoms and one oxygen atom. It is not considered a heteroaromatic compound because it lacks the aromaticity characteristic, despite being a heterocyclic compound. Thus, statement (c) is incorrect.

Step 4: Considering Homologues and Isomerism

Homologous compounds are a series of compounds that differ from each other by a repeating unit, typically \ \( -CH_2- \ \). Generally, they are not isomers of each other because they contain a different number of atoms. Therefore, statement (d) is correct.

Key Concepts

IUPAC Nomenclature

The IUPAC nomenclature system is a standardized way to name chemical compounds. It's essential for communicating complex molecule structures clearly. When naming dicarboxylic acids, the main carbon chain is identified, and substituents like carboxylic acid groups are numbered.
For example, succinic acid, which has the molecular formula \((CH_2)_2(COOH)_2\), is correctly named Butanedioic acid, not Ethane 1,2-dicarboxylic acid. Here, "butane" indicates a four-carbon chain, and "dioic" shows two carboxylic acid groups attached. This systematic approach ensures precision and avoids confusion in the vast world of organic chemistry.

Enantiomers

Enantiomers are a type of stereoisomer. They are non-superimposable mirror images of each other, much like your left and right hands. Though they share the same molecular formula, their 3D arrangement in space differs. A classic example is the pair D- and L-glucose.
It's crucial to note that enantiomers often display different biological activities. For instance, one enantiomer of a drug could be therapeutic, while its mirror image might be inactive or even harmful. Enantiomers do not have identical biological properties due to their interactions with chiral environments in biological systems, such as enzymes and receptors, which are also chiral.

Heteroaromatic Compounds

Heteroaromatic compounds are a fascinating group of organic molecules that contain at least one atom other than carbon in their aromatic ring. These atoms, known as heteroatoms, are often nitrogen, oxygen, or sulfur. A well-known heteroaromatic compound is pyridine, which includes a nitrogen atom in place of one carbon in the benzene ring.
These compounds share the aromatic characteristics, being cyclic, planar, and exhibiting a particular kind of stability due to electron delocalization. However, Tetrahydrofuran (THF) is not a heteroaromatic compound; it's a heterocyclic compound but lacks the planar structure and conjugated pi-orbital system necessary for aromaticity. Thus, while being heterocyclic, THF doesn't fit the aromatic criteria.

Homologous Series

Organic chemistry is full of diversity, yet homologous series help make sense of it all. They are series of compounds where each member differs by a repeating unit, typically a \( -CH_2- \) group. This pattern ensures they share similar chemical properties, such as methanol, ethanol, and propanol, all being alcohols.
However, because each member of a homologous series differs by entire groups of atoms, they are not isomers. Isomers share the same molecular formula but differ in structure, whereas homologues have different formulas. This distinction is key to understanding the relationship and differences within chemical families.