Question

Why do we sometimes use zig-zag representation of organic formulae?

Answer 1

Because the chain tries to represent 3-dimensional bonds, and each `C-C-H` or `H-C-H` bond angle is around `109.5^@`.

Explanation:

The zig-zag arises from our attempt to draw a three-dimensional structure, on two-dimensional paper. We tend to draw these structures as straight chains, i.e. with the greatest symmetry possible. In actuality, the carbon chain is wiggling about all over the place.

Note that if we have represented `C-C` bonds in the plane, the other 2 bonds attached to carbon project into and out of the page; wedges and dashes are used to represent these bonds.