Chapter 2 Practice Problems

Warm up with naming, conformations, and basic alkane reactivity. Reveal answers after trying each one.

Nomenclature & Properties

1. Name the alkane with formula C₆H₁₄ that has two methyl groups on C-2 of a butane chain.

   Answer

   2,2-Dimethylbutane.

2. Which has the higher boiling point: n-hexane or 2,2-dimethylbutane (shown below)?
   

   Answer

   n-Hexane; less branching → stronger dispersion forces.

Conformational Analysis

3. For butane, which Newman conformer about C2–C3 is lowest in energy: anti, gauche, or eclipsed?

   Answer

   Anti (methyl groups 180° apart). Gauche is higher; eclipsed is highest.

4. In methylcyclohexane, is the equatorial or axial conformation lower in energy? Why?

   Answer

   Equatorial; it avoids 1,3-diaxial steric interactions.

Reactivity

5. Propane chlorination gives two products. Which is major?
   

   Answer

   2-Chloropropane (secondary radical favored over primary).

6. Balance the combustion of cyclopentane.
   

   Answer

   2 C₅H₁₀ + 15 O₂ → 10 CO₂ + 10 H₂O.