Cycloalkanes and Substituted Cyclohexane Conformations

A set of 10 vocabulary flashcards defining key concepts, strain types, conformations, and energetic properties of cycloalkanes.

Angle strain

The instability introduced into a molecule when bond angles deviate from the ideal $109^\bullet$ bond angle of an $sp^3$ hybridized carbon.

1,3-diaxial interaction

A steric strain interaction occurring between an axial substituent and axial hydrogens on 1,3-related ring carbons, which is energetically equivalent to a gauche butane interaction.

A-values

Values determined from equilibrium measurements that represent the energy difference between equatorial and axial chair conformations, serving as a general measure of a substituent's steric size.

Chair conformation

The lowest energy conformation of cyclohexane with no strain energy and bond angles of $111^\bullet$, where all C-H bonds are staggered.

Axial position

Positions in a cyclohexane chair conformation where the six bonds or hydrogens are oriented parallel to the principal molecular axis.

Equatorial position

Positions in a cyclohexane chair conformation where the six bonds or hydrogens are oriented perpendicular to the principal molecular axis.

Boat conformation

A transition state structure at an energy maximum during cyclohexane conformational interconversion, destabilized by eclipsing interactions and transannular flagpole strain.

Twist-boat conformation

A characteristic conformation of cyclohexane that is higher in energy than the chair form ($5.3\,kcal\,mol^{-1}$ relative energy) but represents an energy minimum on the reaction coordinate.

Conformational flipping

The process by which cyclohexane interconverts between chair forms with an activation energy of $10.8\,kcal\,mol^{-1}$, turning all axial positions into equatorial positions and vice versa.

Heat of combustion

The amount of heat released when a cycloalkane is burned completely in oxygen, used experimentally to determine the amount of strain energy present in the molecule.