1. Single bonds rotate, so one molecule samples many conformations.
Because a σ (single) bond spins freely, the same molecule constantly twists into different conformations — these are shapes of one molecule, not separate isomers.
2. Staggered is the lowest-energy arrangement.
Looking straight down a C–C bond, staggered means the three front bonds sit 60° offset from the back bonds, spreading electrons out and minimizing repulsion.
3. Eclipsed is the highest-energy arrangement.
When the front and back bonds line up at 0° they crowd each other, and this torsional strain makes the eclipsed form an energy maximum the molecule passes through, not a resting point.
4. For ethane the staggered-to-eclipsed barrier is about 2.9 kcal/mol.
Ethane rolls between three identical staggered valleys and three eclipsed peaks, so the energy curve is a gentle wave only ~2.9 kcal/mol tall — small, but real.
5. Butane splits its staggered forms into anti and gauche.
Looking down butane's C2–C3 bond, the anti conformer holds the two CH₃ groups 180° apart (lowest), while a gauche staggered form (60° apart) sits ~0.9 kcal/mol higher from steric strain.
6. Summary
Single bonds rotate freely · staggered = 60° offset, lowest energy · eclipsed = 0° aligned, highest energy (torsional strain) · ethane barrier ≈ 2.9 kcal/mol · butane: anti < gauche (~0.9 kcal/mol) < eclipsed · molecules spend most time in the lowest-energy staggered/anti forms.
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No — they are conformations of the same molecule, related only by rotation about the C–C bond, not different compounds.
Staggered — its bonds sit 60° apart, minimizing electron–electron repulsion, whereas eclipsed bonds align at 0° and suffer torsional strain.
About 2.9 kcal/mol between each staggered valley and eclipsed peak.
Both are staggered, but anti keeps the two CH₃ groups 180° apart (lowest energy) while gauche places them 60° apart, ~0.9 kcal/mol higher from steric strain.
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