Question

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.
Choose the correct answer from the options given below:

• A. A, B and C only
• B. B, C and D only
• C. A, B and E only
• D. C, D and E only

Hint:

To solve isomerism questions, have clear definitions in mind:
- \textbf{Chain Isomers:} Different carbon skeleton.
- \textbf{Positional Isomers:} Same skeleton, different position of functional group/substituent/multiple bond.
- \textbf{Functional Isomers:} Different functional groups.
- \textbf{Metamers:} Different alkyl groups around a polyvalent functional group (e.g., -O-, -S-, -NH-, -COO-).
- \textbf{Stereoisomers:} Same connectivity, different spatial arrangement (Geometrical & Optical).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:

The question asks us to identify the correct statements related to different types of isomerism for given pairs of organic compounds. Each statement must be evaluated using the definitions of functional isomerism, metamerism, optical isomerism, positional isomerism, and chain isomerism.

Step 2: Detailed Analysis of Each Statement:

A. Propanal and propanone are functional isomers.

Propanal (CH₃CH₂CHO) is an aldehyde, while propanone (CH₃COCH₃) is a ketone. Both have the same molecular formula, C₃H₆O, but different functional groups. Isomers having the same molecular formula but different functional groups are called functional isomers.
Conclusion: Statement A is correct.

B. Ethoxyethane and methoxypropane are metamers.

Ethoxyethane has the structure C₂H₅–O–C₂H₅, while methoxypropane has the structure CH₃–O–C₃H₇. Both are ethers and have the same molecular formula, C₄H₁₀O. Metamers are isomers having the same functional group but different alkyl groups attached on either side of the functional group.
Conclusion: Statement B is correct.

C. But-2-ene shows optical isomerism.

But-2-ene has the structure CH₃–CH=CH–CH₃. For optical isomerism, a molecule must be chiral, usually containing a carbon attached to four different groups. But-2-ene has no chiral carbon. Although it shows geometrical (cis–trans) isomerism, neither isomer is optically active.
Conclusion: Statement C is incorrect.

D. But-1-ene and but-2-ene are functional isomers.

But-1-ene (CH₂=CH–CH₂–CH₃) and but-2-ene (CH₃–CH=CH–CH₃) both contain the same functional group (alkene). They differ only in the position of the double bond. Such isomerism is called positional isomerism, not functional isomerism.
Conclusion: Statement D is incorrect.

E. Pentane and 2,2-dimethylpropane are chain isomers.

Pentane (CH₃CH₂CH₂CH₂CH₃) and 2,2-dimethylpropane (C(CH₃)₄) both have the molecular formula C₅H₁₂. They differ in the arrangement of the carbon skeleton. Isomers differing in carbon chain structure are called chain isomers.
Conclusion: Statement E is correct.

Step 3: Final Answer:

The correct statements are A, B, and E.
Therefore, the correct option is (C).