Intramolecular vs. Intermolecular Reaction
In some reactions, two pathways present themselves: one via an intramolecular reaction (reacting groups both within the same molecule), one via an intermolecular reaction (reacting groups in different molecules). Generally intramolecular reactions are entropically favoured.
In an intermolecular reaction, one molecule is made for every two consumed, so the amount of 'disorder' in the system decreases. This is entropically disfavourable.
In an intramolecular reaction this is not the case, so these reactions have an entropically favourability over intermolecular reactions.