Steric Control of Alkane Conformation

Alkanes prefer structures that stagger bonds on adjacent tetrahedral carbons (see Chapter 5, Problem 1). However, steric repulsion can affect the relative energies of staggered conformations. 

Which conformation is more stable, anti or gauchel What evidence is there for steric repulsion between methyl groups in the gauche conformation (Hint Look for distortions in the CCC bond angles as a function of conformation.) 

Internal rotation in isooctane (2,2,4-trimethylpentane) creates a large number of staggered conformations. However, only rotation about the C3-C4 bond produces conformations with different structures. Plot the energy of isooctane (vertical axis) vs. HCCCtBu torsion angle, i.e., about the C3-C4 bond (horizontal axis). How many minimum energy structures are there Are they all fully staggered Draw Newman projections that show the conformation of these structures. How does steric repulsion affect isooctane conformation  

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