In general, which one of the following statements is NOT CORRECT?
Hydrogen bonds result from electrostatic interactions
Hydrogen bonds contribute to the folding energy of proteins
Hydrogen bonds are weaker than van der Waals interactions
Hydrogen bonds are directional
ANSWER
The statement that is not correct is (C): hydrogen bonds are stronger, not weaker, than van der Waals interactions.
Official answer: CSource: Official answer key, GATE 2019 BT (IIT Madras)
We need the statement that is false, so test each option against what is known about non-covalent forces.
(A) A hydrogen bond is mainly an electrostatic (dipole-dipole) attraction between a donor (with = N, O, F) and an acceptor lone pair. The statement is correct.
(B) Backbone and side-chain hydrogen bonds stabilise -helices, -sheets and tertiary structure, so they contribute to the folding energy of proteins. The statement is correct.
(C) A hydrogen bond has an energy of about to . A van der Waals contact is only about to . So hydrogen bonds are stronger than van der Waals interactions, and the statement that they are weaker is false.
(D) Hydrogen bonds are strongest when the donor, hydrogen and acceptor are nearly collinear, so they are directional. The statement is correct.
The statement that is NOT correct is (C).
KEY IDEA
Typical strength order of non-covalent forces: ionic and hydrogen bonds (roughly 12 to 30 kJ/mol) are stronger than van der Waals contacts (roughly 0.4 to 4 kJ/mol). Hydrogen bonds are electrostatic in origin and directional.
WATCH OUT FOR
Treating hydrogen bonds as 'weak' and assuming they are weaker than every other non-covalent force. They are weak compared with covalent bonds, but stronger than van der Waals forces, and much of their value comes from being directional.
From the GATE 2019 BT paper. Every question of this paper · Download the full paper · All 12 Biomolecules questions, with notes
