The Pauli exclusion principle applies to all fermions, right? And protons are fermions. So if you consider a water molecule, and swap the protons in the two hydrogens, shouldn't the wavefunction of the entire molecule acquire a negative sign?
And if so, what are the implications of this? Does this have a noticeable impact on the chemistry of water, or are the hydrogens too far apart for it to make any significant difference?
(In quantum chemistry, there's a big issue called electron-electron correlation that complicates calculations. Would proton-proton correlation have a similar effect?)