Question

1,3-butadiene is drawn in the s-cis (cisoid) conformation in the introduction. Is this the preferred conformation? Explain. Why is the s-cis conformation shown?

Answer 1

There is no reason to prefer one to the other.

Explanation:

Since the middle bond between `C_2-C_3` is single, it can rotate freely.
Only if the `H`'s around that bond were replaced by other atoms, that either reject or attract one another, would there be a preferred (not obligate) position.
If not, then everything depends on physical circumstances like temperature and pressure.