JEE Main · 2006 · 30 Apr 2006 · Offline · General Organic Chemistry

The three limiting arrangements of 2-fluoroethanol are ranked by torsional strain together with a special stabilising contact. The eclipsed form suffers maximum torsional strain and is least stable. The gauche form brings the $-\mathrm{OH}$ and $-\mathrm{F}$ close enough for an intramolecular hydrogen bond, which stabilises it beyond anything the anti form gains from relief of strain, so the gauche form is the most stable, with the anti form in between. Stability therefore increases in the order eclipse $<$ anti $<$ gauche.