Chemistry · Chemical Bonding · NEET
Both are the same type of attraction: an H atom held between two electronegative atoms (F, O or N). The only difference is WHERE the two atoms sit. Intramolecular = both atoms are inside the SAME single molecule (example: o-nitrophenol, where -OH bonds to the neighbouring -NO2). Intermolecular = the two atoms belong to TWO DIFFERENT molecules (example: HF, water, alcohols, carboxylic acid dimers). Trick word split: intrA = A single molecule; intER = bEtwEEn molecules.
In ortho-nitrophenol the -OH and -NO2 are next to each other, so hydrogen bonding happens INSIDE the same molecule (intramolecular). That H atom is now busy, so molecules do not stick to each other. In para-nitrophenol the two groups are far apart, so each molecule H-bonds to OTHER molecules (intermolecular). Intermolecular bonding glues molecules together, so more heat is needed to separate them. Result: para boils higher, ortho boils lower and is steam-volatile. NEET loves this exact comparison.
Two conditions from NCERT. (1) An H atom must be covalently attached to a highly electronegative and small atom, only F, O or N. (2) This makes the H partially positive, so it can attract the lone pair of another electronegative atom (F, O or N). No F, O or N means no true hydrogen bond. So H-Cl or H-C do NOT count, even though Cl is electronegative, because Cl is too big and less electronegative for a strong H-bond.
Carboxylic acids form TWO intermolecular hydrogen bonds at once and join into pairs called dimers (a cyclic double H-bond). This is stronger and more extensive than the single H-bond chain in alcohols. Breaking two H-bonds needs more heat, so acids boil higher than aldehydes, ketones and even alcohols of similar molecular mass. This is NEET 2018.
For raising boiling point, intermolecular is what matters, because it links separate molecules together. Intramolecular bonding stays inside one molecule and does NOT link molecules, so it actually lowers boiling point compared to the isomer that bonds intermolecularly. So the trick for NEET: intramolecular molecule = more volatile, lower boiling point; intermolecular molecule = less volatile, higher boiling point.
Intramolecular hydrogen bonding is present in which of the following compounds? Choices include p-nitrophenol, m-nitrophenol, HF and o-nitrophenol.
Which one of the following compounds shows the presence of intramolecular hydrogen bond?
Carboxylic acids have higher boiling points than aldehydes, ketones and even alcohols of comparable molecular mass. This is due to their:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Weaker. A hydrogen bond is only a strong attraction, not a full shared-electron bond. It is shown by a dotted line, while a covalent bond is a solid line. But it is stronger than ordinary van der Waals forces, which is why it strongly affects boiling point and structure.
For NEET, only F, O and N form true hydrogen bonds with H. Chlorine is quite electronegative but too large, so H-Cl does not form a real hydrogen bond of comparable strength. Stick to F, O, N in the exam.
HF forms strong intermolecular hydrogen bonds because F is small and highly electronegative. HCl cannot form these H-bonds, so it has much weaker forces and a lower boiling point, even though it is heavier.
By steam distillation. o-nitrophenol has intramolecular H-bonding, so it is volatile and travels with steam. p-nitrophenol has intermolecular H-bonding and stays behind. This is exactly NEET 2017.
It lowers it compared to the isomer with intermolecular bonding. Because the H-bond is locked inside one molecule, molecules do not stick to each other, so the substance is more volatile.
