JEE Main · 2021 · 27 Aug 2021 · Shift 2 · Chemical Bonding and Molecular Structure

In $o$-nitrophenol the hydroxyl hydrogen and the neighbouring nitro oxygen form an intramolecular hydrogen bond, so little remains for intermolecular association. In $2,6$-di-$tert$-butyl-$4$-methylphenol the two bulky $tert$-butyl groups flanking the $-\mathrm{OH}$ shield it and block the approach of a second molecule. In $p$-hydroxyacetanilide the $-\mathrm{OH}$, $-\mathrm{NH}$ and $\mathrm{C}=\mathrm{O}$ groups are unhindered and outward-pointing, allowing extensive hydrogen bonding between molecules. Only $p$-hydroxyacetanilide shows significant intermolecular hydrogen bonding.