Four of the following five words are alike in a certain way and so form a group. Which is the one that does not belong to that group? Diverge, Separate, Disjoin, Split, Unify

Four letter-pairs are given below. The letters on the left side of (-) are related to the letters on the right side following a specific logic/rule. Three of them share the same rule. Select the odd one out.

Four letter-pairs are given. The letters on the left side of (-) are related to the letters on the right side of (-) by some logic. Three of them follow the same logic. Select the odd one out.