Use these interaction energies: eclipsed H/H 4.0 kJ/mol, eclipsed CH3/H 6.0 kJ/mol, eclipsed CH3/CH3 11 kJ/mol (no other terms). In a Newman projection along C2-C3 of butane, the front carbon has CH3 at 12 o'clock and H at 4 and 8 o'clock. The rear carbon has CH3 at 4 o'clock and H at 12 and 8 o'clock. The strain energy of this conformation relative to a strain-free staggered conformation is:

JEE Main levelSingle correct optionDifficulty 2 of 3st095

Use these interaction energies: eclipsed H/H $4.0 kJ/mol$ , eclipsed $CH X_{3}$ /H $6.0 kJ/mol$ , eclipsed $CH X_{3}$ / $CH X_{3}$ $11 kJ/mol$ (no other terms). In a Newman projection along C2-C3 of butane, the front carbon has $CH X_{3}$ at 12 o'clock and H at 4 and 8 o'clock. The rear carbon has $CH X_{3}$ at 4 o'clock and H at 12 and 8 o'clock. The strain energy of this conformation relative to a strain-free staggered conformation is:

All groups are eclipsed (dihedral

0^{\circ}

pairs at 12, 4 and 8 o'clock). At 12 o'clock front

CH X_{3}

meets rear H (

6.0

), at 4 o'clock front H meets rear

CH X_{3}

(

6.0

), and at 8 o'clock H meets H (

4.0

). The total is

6.0 + 6.0 + 4.0 = 16

kJ/mol. The case with the two methyls eclipsed (19 kJ/mol) does not apply here.