Q.

1. Observe the following structures and answer the questions given below.

Step 1. Relation between (i) and (ii) (part a). (i) CH3-CH2-CH2-CHO (butanal, straight chain) and (ii) CH3-CH(CH3)-CHO (2-methylpropanal, branched chain) share the same molecular formula, C4H8O, and the same functional group (aldehyde), but have DIFFERENT carbon skeletons (straight vs branched) -- by section 14.5.1(a), this is chain isomerism, and the two are chain isomers.

Step 2. IUPAC name of (ii) (part b). CH3-CH(CH3)-CHO: parent = propane-based aldehyde chain (propanal numbering puts the CHO carbon at C1), methyl substituent at C2. Since the CHO carbon is always C-1 by rule (section 14.4.7), the name is 2-methylpropanal. …

Comparing molecular formula, functional group, and carbon skeleton between (i) and (ii) against section 14.5.1's isomerism definitions, then applying section 14.4.7's aldehyde-naming rule …

• Naming (ii) as if the methyl were at C3 instead of C2 (the CHO carbon, always C-1, forces the branch onto C2 for this structure). …