Question

In numbering carbon atoms in the parent chain of a hydrocarbon, why would you number from right to left, rather than left to right?

Answer 1

it depends on which side is closest to the functional groups or branches. You start from the side that gives you minimum numbers. EG: CH3-CH2-CHBr-CH3
is 2-Bromobutane not 3-Bromobutane
There is actually no right and left, you mirror it and it's reversed.