Pentane, lowest energy conformation

Among the most widespread classes of acyclic compounds to exhibit stereoelectronic control over conformation are acetals. Take the simple acetal of formaldehyde and methanol, for example what is its conformation An obvious suggestion is to draw it fully extended so that every group is fully anti-periplanar to every other—this would be the lowest-energy conformation of pentane, which you get if you just replace the Os with CH2S. 

For any open-chain single bond that connects two sp carbon atoms, an inhnite number of conformations are possible, each of which has a certain energy associated with it. As a practical matter, the number of conformations is much less. If one ignores duplications due to symmetry, the number of conformations can be estimated as being greater than 3", where = the number of internal C—C bonds. -Pentane, for example, has 11, -hexane 35, w-heptane 109, -octane 347, n-non-ane 1101, and n-decane 3263. For ethane there are two extremes, a conformation of highest and one of lowest potential energy, depicted in two ways as ... 

Draw Newman projections for the staggered and eclipsed conformations of pentane for rotation about the C2—C3 bond. Which conformation is lowest in energy ... 

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