# What bonding occurs in "ethylene glycol"?

Within the molecule, there are strong $H - C$, and $C - C$, and $C - O$, and $O - H$ covalent bonds. Between molecules, there is hydrogen bonding and dispersion forces.
Hydrogen bonding occurs when hydrogen is bound to a strongly electronegative element, $O$ or $F$ or $N$. The heteroatom polarizes electron density towards itself, and acquires a partial negative charge. Conversely, the hydrogen acquires a partial positive charge because the heteroatom has denuded it (slightly!) of electron density. This is, in a nutshell, the phenomenon of hydrogen bonding, which is responsible for the exceptionally high boiling points of $O {H}_{2}$, and $H F$, and $N {H}_{3}$.
Thus between molecules, there is an additional electrostatic interaction. The dipoles line up, positive to negative. Ethylene glycol, $H O {H}_{2} C - C {H}_{2} O H$ has two polar hydroxyl groups, and the dipoles line up from molecule to molecule. This constitutes a potent intermolecular force, which accounts for the high boiling point of ethylene glycol, $197.3$ ""^@C, and also its viscosity.