Organic Chemistry – Some Basic Principles Part 3

Concept:Isomerism includes functional, metamer, chain, and optical types based on structure and molecular formula.Explanation:Statement A: Propanal ($\mathrm{CH_3CH_2CHO}$) and propanone ($\mathrm{CH_3COCH_3}$) have same formula $\mathrm{C_3H_6O}$ but different functional groups. Hence they are functional isomers. Correct.Statement B: Ethoxyethane ($\mathrm{C_2H_5OC_2H_5}$) and methoxypropane ($\mathrm{CH_3OC_3H_7}$) both have formula $\mathrm{C_4H_{10}O}$ with different alkyl groups on oxygen. Thus they are metamers. Correct.Statement C: But-2-ene ($\mathrm{CH_3CH=CHCH_3}$) lacks a chiral carbon (four different groups). It shows geometrical but not optical isomerism. Hence false.Statement D: But-1-ene ($\mathrm{CH_2=CHCH_2CH_3}$) and but-2-ene differ only in double bond position, not functional group. They are position isomers, not functional isomers. False.Statement E: Pentane ($\mathrm{C_5H_{12}}$) and 2,2-dimethylpropane ($\mathrm{C_5H_{12}}$) have same formula but different carbon skeletons. Hence they are chain isomers. Correct.Answer:Correct statements are A, B and E. Option A: A, B and E only.