# Effect of temperature on Hydrogen Bonding?

We had this question in a test and I am not sure of the answer

Q. Temperature changes don't effect the extent of inter and intra molecular hydrogen bonding. State true or false.

I think that raising temperature would increase the kinetic energy of molecules and would thus lead to weakening of inter molecular hydrogen bonds. But am not sure what will happen to intra molecular hydrogen bonds...

For e.g. if ortho-nitrophenol is heated, will the intra molecular hydrogen bonds between hydrogen of the hydroxyl group and oxygen of the nitro group break?

Any ideas/suggestions?

## 1 Answer

Yes. Temperature disrupts bond of all kinds. Heat up a protein hot enough and you can even disrupt its primary structure - the linear sequence of amino acids, and amino acids are held together through covalent bonds. This is why prion contaminated organisms and instruments must be heated to extremely, extremely high temperatures. The question is whether or not the bond will break; the question is simply what temperature.

Take for example nitrous acid, which exhibits two unique $\ce{O-N-O}$ bond angles. One of these bond angles (the smaller one) results from intramolecular hydrogen bonding between the hydrogen and the oxygen on the other end. This occurs because there free-rotation is permitted around the single bonds in the nitrous acid molecule. The energy difference between the two structures is calculated to be $0.45~\mathrm{kcal~mol^{-1}}$ or $1880~\mathrm{J~mol^{-1}}$.

• Do you mean that when heated, the bond rotation becomes possible and the energy decreases? – Apurv May 16 '14 at 4:32
• I mean heat will increase rotation and disrupt the intramolecular hydrogen bond. I expect bond rotation to be possible at all temperatures. The non-hydrogen bonded nitrous acid molecule is also actually the lower energy one. – Dissenter May 16 '14 at 4:33