axial (equatorial)

Also contains definitions of: pseudo-axial, pseudo-equatorial, quasi-axial, quasi-equatorial
In the chair form of cyclohexane ring bonds to ring atoms (and molecular entities attached to such bonds) are termed axial or @[email protected] according to whether the bonds make a relatively large or small @[email protected], respectively, with the plane containing or passing closest to a majority of the ring atoms. Thus the axial bonds are approximately parallel to the C3 axis and the @[email protected] bonds approximately parallel to two of the ring bonds. These terms are also used for the chair form of other saturated six-membered rings. The corresponding bonds occurring at the allylic positions in mono-unsaturated six-membered rings are termed pseudo-axial (or quasi-axial) and pseudo-equatorial (or quasi-equatorial). The terms axial and @[email protected] have similarly been used in relation to the puckered @[email protected] of cyclobutane, @[email protected] @[email protected] of cyclooctane, etc. and the terms pseudo-axial and pseudo-equatorial in the context of the non-planar structures of cyclopentane and cycloheptane.
See @[email protected] for an alternative use of axial and @[email protected] with bipyramidal structures.
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2200 [Terms] [Paper]