Eclipsed conformation

A molecular conformation in which bonds on adjacent atoms align when viewed along the bond connecting those atoms. This alignment creates torsional strain in many molecules.

Torsional strain: The increase in molecular energy caused by repulsive interactions between bonding electron pairs on adjacent atoms. The aligned bonds create this strain, raising the conformation’s energy.
Molecular conformation: A spatial arrangement of atoms in a molecule that can change through rotation around bonds. Eclipsed geometry is one member of this broader class of arrangements.
Staggered conformation: A molecular conformation in which bonds on adjacent atoms are offset when viewed along the bond connecting those atoms. It is the lower-energy alternative to eclipsing in ethane.
Conformational analysis: The study of how molecular shapes and their relative energies change through bond rotation. It uses eclipsed arrangements to compare conformational energies and rotational barriers.
Dihedral angle: The angle between two planes defined by four atoms connected in sequence. A zero-degree dihedral angle describes bonds that are eclipsed.
Constitutional isomer: One of two or more compounds with the same molecular formula but different atom connectivity. Conformations differ by spatial arrangement, not by the connectivity that distinguishes these isomers.
Syn-pentane interaction: A steric interaction between two methyl groups brought close together by rotation around bonds in a carbon chain. It can destabilize a staggered conformation, showing that eclipsing is not the only source of conformational strain.
Butane: A four-carbon alkane with molecular formula C₄H₁₀. Its rotation includes eclipsed arrangements with different degrees of substituent crowding.
Ethane: A two-carbon alkane with molecular formula C₂H₆. Its rotation provides the simplest example of eclipsed and staggered conformations.
Newman projection: A drawing that represents a molecule as viewed along a bond between two atoms. This projection makes the alignment of adjacent bonds easy to inspect.

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