Absence of Sn axis

The absence of an Sn axis in a molecule or compound signifies several things.

Geometrical Isomerism

One of the implications of the absence of an Sn axis is geometrical isomerism. Geometrical isomers are compounds that have the same molecular formula but differ in the arrangement of atoms or groups around a double bond or ring. They do not have a mirror image relationship and cannot be superimposed on each other.

Optical Activity

Another implication of the absence of an Sn axis is optical activity. Optical activity is the ability of a substance to rotate the plane of polarization of plane-polarized light. It occurs in chiral molecules, which are molecules that are non-superimposable on their mirror images. When a chiral molecule is placed in a plane-polarized light, the light is rotated either clockwise or counterclockwise.

Trans Isomer

The absence of an Sn axis does not necessarily signify a trans isomer. Trans isomers are compounds that have the same molecular formula and the same connectivity of atoms but differ in the arrangement of atoms or groups on opposite sides of a double bond or in a ring. They have a mirror image relationship and can be superimposed on each other.

Tetrahedral Point Group

The absence of an Sn axis does not necessarily signify a tetrahedral point group. A tetrahedral point group is a point group that has four C3 axes, three C2 axes, and six σ planes of symmetry. It is characteristic of molecules with tetrahedral geometry, which have four atoms or groups of atoms bonded to a central atom.

In conclusion, the absence of an Sn axis denotes geometrical isomerism and optical activity but does not necessarily signify a trans isomer or a tetrahedral point group.