Which of the following structures is different from the other three in terms of isomerism?

• A. n-butane (CH_3CH_2CH_2CH_3)
• B. isobutane (CH_3CH(CH_3)_2)
• C. n-butane (CH_3CH_2CH_2CH_3)
• D. n-butane (CH_3CH_2CH_2CH_3)

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the concept of isomerism. Isomers are compounds that have the same molecular formula but different arrangements of atoms. There are different types of isomerism, such as structural (constitutional) isomerism and stereoisomerism.
2. Step 2: Identify the molecular formula of the compounds given. Both n-butane and isobutane have the molecular formula C4H10, meaning they are isomers of each other.
3. Step 3: Analyze the structures of n-butane and isobutane. n-Butane is a straight-chain alkane, while isobutane is a branched-chain alkane. This difference means they are structural isomers.
4. Step 4: Recognize that the three n-butane structures are identical and represent the same compound, so they are not isomers relative to each other.
5. Step 5: Conclude that isobutane differs from the other three n-butane structures because it is a structural isomer with a different connectivity of atoms, while the others are identical.