physical chemistry - Strength of intramolecular vs intermolecular hydrogen bonds

Why are intramolecular hydrogen bonds weaker than intermolecular hydrogen bonds?

Answer

I don't think there is much of a difference between the strengths of intramolecular or intermolecular hydrogen bonds.

However the strength of interactions between molecules depends on the type of hydrogen bond.

Consider a typical example: ortho-Nitrophenol has a lower melting and boiling point than para-Nitrophenol.

The interactions between molecules are much stronger when there are intermolecular hydrogen bonds (as in para-Nitrophenol) because the bonds are formed between molecules. This results in more stability and lower melting and boiling points (which might appear to be because of stronger bonds) because the molecules prefer to be closer to each other.

If intramolecular hydrogen bonds are present (as in the case of ortho-Nitrophenol) the interactions within individual molecules are greater and so there is less attraction between molecules. This causes less stability and higher melting and boiling points because the molecules are not really attracted to each other much and not because the hydrogen bonds are weaker.