In General Relativity, locally all reference frames are flat. This does not change at the event horizon, chemistry continues to work normally. It is just that in the time it takes for half the molecule to affect the other half, the other half will have slipped across the event horizon.

There is a classic analogy of light traveling through space-time being like ants crawling on a balloon. A black hole is a spot where the balloon is being sucked in. Faster and faster as you get closer. The event horizon is where the speed at which the balloon moves matches the speed of the ant. There is nothing special from the ant's immediate perception about this line, but if the ant crosses, it is doomed.