Now on the inside of the DNA we have these bases. The question is why exactly does this interaction actually take place? Why is it favorable from the inter molecular perspective, from the intermolecular interaction perspective? Well, number one is on the inside of the DNA molecule we have these bases that are able to form hydrogen bonds. So we have one base that interacts with a complementary base on the other single strand molecule and that forms our hydrogen bond. So in this case, this is hydrogen bonding and this is also hydrogen bonding.