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 @E02174@ according to whether the bonds make a relatively large or small @A00346@, 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 @E02174@ 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 @E02174@ have similarly been used in relation to the puckered @C01258@ of cyclobutane, @C01421@ @C01262@ of cyclooctane, etc. and the terms pseudo-axial and pseudo-equatorial in the context of the non-planar structures of cyclopentane and cycloheptane.
See @A00415@ for an alternative use of axial and @E02174@ with bipyramidal structures.
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2200 [Terms] [Paper]