Identify correct statements: Propanal and propanone are functional isomers. Ethoxyethane and methoxypropane are metamers. But-2-ene optical isomerism. But-1-ene and but-2-ene. Pentane and 2,2-dimethyl propane.
Identify correct statements from the following :

A. Propanal and propanone are functional isomers.
B. Ethoxyethane and methoxypropane are metamers.
C. But-2-ene shows optical isomerism.
D. But-1-ene and but-2-ene are functional isomers.
E. Pentane and 2, 2-dimethyl propane are chain isomers.

(A) A, B and E only

(B) A, B and C only

(C) C, D and E only

(D) B, C and D only

Correct Answer: A
Statements A, B, and E are correct

Detailed Statement Analysis

Statement A: Correct.
Propanal (\(CH_3CH_2CHO\)) is an aldehyde and Propanone (\(CH_3COCH_3\)) is a ketone. They both have the same molecular formula (\(C_3H_6O\)) but different functional groups, making them functional isomers.

Statement B: Correct.
Metamers are isomers that differ in the distribution of carbon atoms on either side of a polyvalent functional group (like \(-O-\)).
• Ethoxyethane: \(CH_3CH_2 - O - CH_2CH_3\) (2 carbons on each side)
• Methoxypropane: \(CH_3 - O - CH_2CH_2CH_3\) (1 carbon vs 3 carbons)
Both share formula \(C_4H_{10}O\).

Statement C: Incorrect.
But-2-ene (\(CH_3-CH=CH-CH_3\)) shows geometrical isomerism (cis and trans), but it does not show optical isomerism as it lacks a chiral carbon atom.

Statement D: Incorrect.
But-1-ene and But-2-ene have the same molecular formula (\(C_4H_8\)) and the same functional group (alkene). They only differ in the position of the double bond, making them position isomers, not functional isomers.

Statement E: Correct.
Both Pentane (\(CH_3CH_2CH_2CH_2CH_3\)) and 2,2-Dimethylpropane (\(C(CH_3)_4\)) share the molecular formula \(C_5H_{12}\) but differ in the arrangement of the carbon skeleton (straight chain vs branched), qualifying them as chain isomers.

Fundamental Theory: Structural Isomerism

1. Chain Isomerism

Occurs when compounds have the same molecular formula but different carbon skeletons. This usually happens due to branching of the main carbon chain. For example, n-butane and isobutane are chain isomers.

2. Position Isomerism

Occurs when the same functional group or substituent is attached at different positions on the same carbon skeleton. A classic example is 1-propanol and 2-propanol.

3. Functional Isomerism

Occurs when compounds have the same molecular formula but different functional groups. Common pairs include:

  • Alcohols and Ethers (\(C_nH_{2n+2}O\))
  • Aldehydes and Ketones (\(C_nH_{2n}O\))
  • Carboxylic acids and Esters (\(C_nH_{2n}O_2\))

4. Metamerism

This is a special type of structural isomerism where the nature of alkyl groups attached to the same polyvalent functional group differs. It is common in ethers, thioethers, secondary amines, and esters.

5. Geometrical vs. Optical Isomerism

Stereoisomerism is divided into:

  • Geometrical: Restricted rotation (like in alkenes) leading to Cis/Trans forms.
  • Optical: Presence of a chiral center (carbon with 4 different groups) leading to non-superimposable mirror images.

Related JEE Main Questions

Identify the correct statements. A. Arginine and Tryptophan are essential amino acids. B. Histidine does not contain heterocyclic ring in its structure. C. Proline is a six membered cyclic ring amino acid. D. Glycine does not have chiral centre. E. Cysteine has characteristic feature of side chain as MeS – CH₂ – CH₂ –. Choose the correct answer from the options given below : (A) C and D Only (B) A and D Only (C) C and E Only (D) B and E Only
MnO₄²⁻, in acidic medium, disproportionates to : (A) MnO₄⁻ and MnO (B) MnO₄⁻ and MnO₂ (C) Mn2O₇ and MnO₂ (D) Mn2O₇ and MnO
80 mL of a hydrocarbon on mixing with 264 mL of oxygen in a closed U-tube undergoes complete combustion. The residual gases after cooling to 273 K occupy 224 mL. When the system is treated with KOH solution, the volume decreases to 64 mL. The formula of the hydrocarbon is : (A) C2H2 (B) C2H4 (C) C4H10 (D) C2H6
Given below are two statements : Statement I: When an electric discharge is passed through gaseous hydrogen, the hydrogen molecules dissociate and the energetically excited hydrogen atoms produce electromagnetic radiation of discrete frequencies. Statement II : The frequency of second line of Balmer series obtained from He+ is equal to that of first line of Lyman series obtained from hydrogen atom. In the light of the above statements, choose the correct answer from the options given below :
Given below are two statements: Statement I: The number of pairs among [SiO₂, CO₂], [SnO, SnO₂], [PbO, PbO₂] and [GeO, GeO₂], which contain oxides that are both amphoteric is 2. Statement II: BF₃ is an electron deficient molecule, can act as a Lewis acid, forms adduct with NH₃ and has a trigonal planar geometry. In the light of the above statements, choose the correct answer:

Frequently Asked Questions (FAQs)

1. Can but-2-ene ever be optically active? No. But-2-ene lacks a chiral center (a carbon with four distinct groups). It only shows geometrical isomerism.
2. What is the difference between metamers and position isomers? Metamers specifically involve different alkyl groups around a polyvalent functional group (like O or NH), while position isomers involve the functional group moving along the same carbon chain.
3. Are all aldehydes and ketones functional isomers? Only if they have the same molecular formula. For example, Propanal and Propanone are isomers (\(C_3H_6O\)), but Ethanal and Propanone are not.
4. Why are pentane and isopentane called chain isomers? Because they have the same formula (\(C_5H_{12}\)) but pentane is a straight chain while isopentane has a branch.
5. Does but-1-ene show geometrical isomerism? No, because one of the double-bonded carbons is attached to two identical hydrogen atoms.

Expert Contribution by: JEE NEET Experts

Specialists in Organic Chemistry and Isomerism coaching.

Related Covered Topics

jee mainsneetorganic chemistryisomerismfunctional isomersmetamerschain isomersposition isomersoptical isomerismgeometrical isomerismpropanalpropanoneethoxyethanemethoxypropanebutene isomerspentane2,2-dimethylpropanestructural isomerismmolecular formulachiral center
Explore Full Chapter Notes & Practice Papers – neetjeerankers.com
Scroll to Top