Water has 2 distinct nuclear-spin isomers of its hydrogen atoms: para-water and ortho-water. The isomers are stable, though interconversion does mysteriously occur sometimes. Ambient-temperature water is a mixture of these 2 isomers.
Whereas the nuclear spin of the hydrogen atoms in para-water sum to 0 via asymmetric wavefunctions, ortho-water nuclear spins symmetrically sum to 1. The atomic twists and turns of para-water let it react 23% faster than the stolider ortho-water. Para-water is also able to more strongly attract its reaction partner than ortho-water, which leads to enhanced chemical reactivity.