Symmetry is an organizing principle that provides a means for determining both invariance and change. Symmetry analysis may result in the identification of a fundamental region (motif) that is the smallest element required to explain the repetition that forms a pattern. Molecular symmetry (point symmetry) is the description of the symmetry of an isolated molecule, i.e. a set of operations transforming a system about a common point, which usually turns out to be the centre of gravity of a molecule. Crystallographic symmetry - point symmetry + translational symmetry

In this laboratory students are asked to draw molecules, identify symmetry elements and operations.

What is a symmetry element? A symmetry element is a point, line or plane that leaves the molecule unchanged when a symmetry operation is applied to it.

What is a symmetry operation? A symmetry operation is a permutation (transformation) that leaves the object (molecule or crystal) unchanged, i.e. indistinguishable from the starting state.

**E -identity - unity -does nothing****Axis of rotation (C**_{n}): is an axis in which rotation by 360/n leaves the molecule unchanged. n is the order of rotation.**Reflection plane (mirror plane) - reflection through the plane leaves the molecule unchanged - types****Vertical reflection plane (s**_{v})- the plane is parallel to the axis of rotation.**Horizontal reflection plane (s**_{h}) - the plane is perpendicular to the rotation axis**Diagonal plane (s**_{d}) - vertical plane of symmetry that bisects the axis.

**Improper rotation axis (S**_{n}) - Combination of rotation axis (Cn) and horizontal plane of symmetry.**Centre of inversion (i) - is a point in which an atom in position (x,y,z) if moved in a straight line through (i) will have its equivalent at (-x,-y,-z).**

Types:

**Identity****Rotation****Reflection****Inversion****Improper rotation-reflection**

In this laboratory students will use available software (e.g Arguslab, BIOVIA/Accelrys Discovery Studio, Jmol) to draw molecules, and identify symmetry elements and operations. For each molecule; use the software to draw the molecule; identify its symmetry elements and operations:

Additional Symmetry Operations:

Use diagrams to show the location of all symmetry elements:

Additional Symmetry Operations:

Use diagrams to show the location of all symmetry elements:

Additional Symmetry Operations:

Use diagrams to show the location of all symmetry elements:

Additional Symmetry Operations:

Use diagrams to show the location of all symmetry elements:

Additional Symmetry Operations:

Use diagrams to show the location of all symmetry elements:

Additional Symmetry Operations:

Use diagrams to show the location of all symmetry elements:

http://symmetry.otterbein.edu/gallery/

http://www.stolaf.edu/depts/chemistry/mo/struc/

http://wwwchem.uwimona.edu.jm/spectra/jsmol/demos

Copyright © 2013-2016 by Robert John Lancashire, all rights reserved.

Created and maintained by Prof. Robert J. Lancashire,The Department of Chemistry, University of the West Indies,

Mona Campus, Kingston 7, Jamaica.