Torsional strain

Torsional strain is the increase in molecular potential energy associated with eclipsing or partially eclipsing bonds on adjacent atoms. It varies with rotation around a bond.

Dihedral angle: The angle between two intersecting planes, often used to describe rotation around a bond. It quantifies the rotation that determines how eclipsed adjacent bonds are.
Chemical bond: An attraction that holds atoms together through shared electrons or electrostatic forces. Torsional strain concerns the relative alignment of bonds around a shared connection.
Butane: A four-carbon alkane with conformations that differ in energy as its central carbon–carbon bond rotates. Its eclipsed conformers show how torsional strain combines with interactions between larger groups.
Steric strain: An increase in molecular energy caused by unfavorable close contacts between atoms or groups. It is often confused with torsional strain, though its source is nonbonded crowding.
Eclipsed conformation: A molecular conformation in which bonds on adjacent atoms align when viewed along their connecting bond. Its aligned bonds produce a maximum in torsional energy.
Ethane: A two-carbon alkane whose rotation about its carbon–carbon bond interconverts staggered and eclipsed conformations. Its rotation is the simplest standard model for torsional strain.
Cyclohexane: A six-membered carbon ring that adopts nonplanar conformations, especially the chair form. Its chair shape avoids much of the eclipsing found in less favorable ring conformations.
Baeyer strain theory: A theory that attributes the instability of small rings to deviations from the tetrahedral carbon bond angle. It explains ring strain through angle distortion rather than eclipsed bonds.
Staggered conformation: A molecular conformation in which bonds on adjacent atoms are offset when viewed along their connecting bond. Its offset bonds reduce torsional strain relative to the eclipsed arrangement.
Potential energy: Energy associated with the position or arrangement of a system. Torsional strain is an energetic cost of a particular molecular arrangement.

Linked from 12 pages