Question

What is the origin of `"hydrogen-bonding"`?

Answer 1

Hydrogen bonding is not due to `"anomalous expansion"`, whatever that is.

Explanation:

Hydrogen bonding is an intermolecular interaction observed when hydrogen is bound to a strongly electronegative atom such as fluorine, or oxygen, or nitrogen. It is largely responsible for the absurdly high normal boiling points of water, and hydrogen fluoride, `100` `""^@C`, and `19.5` `""^@C` respectively.

Because of the electronegativity of the heteroatom charge separation occurs to give `""^(delta+)H-F^(delta-)` or `""^(delta-)OH_2^(delta+)`, and when the dipoles line up this constitutes a potent intermolecular force.