The molecules can be visualized and represented on a paper by several projection formulae

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Dr. Mohd Kamil Hussain
Department of Chemistry
Govt. Raza P.G. College Rampur, U.P. India
Stereo Chemistry

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Projection Formulas
The molecules can be visualized and represented on a paper by several projection
formulae
1. Wedge-Dash Diagram or Wedge-hash projection.
2. Newman Projection.
3. Sawhorse Projection.
4. Fischer Projection.
5. Haworth projection
Dr. Mohd Kamil Hussain

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Wedge-Dash Diagram or Wedge-hash projection
A wedge and dash projection is used to represent 3D shape of a molecule in which three types of
lines are used in order to represent the three-dimensional structure:
(1) solid lines to represent bonds which are in the plane of the paper
(2) dashed lines to represent bonds that extend away from the viewer
(3) wedge-shaped lines to represent bonds oriented facing the viewer.
Dr. Mohd Kamil Hussain

4. A and C are enantiomers: RR SS
A and B are diastereomers: RR RS
C and B are diastereomers: RS SS
Mirror image, Optically Active
Are not mirror image
B is meso compound : Has plane of symmetry
Dr. Mohd Kamil Hussain

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If the lowest priority group is positioned on the plane of the paper, we can
momentarily exchange it with whatever group happens to be positioned in the
back, then assign configuration, then reverse it.
Mohd. Kamil Hussain, Ph.D

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Newman Projection
A Newman projection visualizes chemical conformations of a carbon-carbon
chemical bond from front to back, with the front carbon represented by a dot and the
back carbon as a circle (see below). The front carbon atom is called proximal, while
the back atom is called distal.

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Shawhorse Projection
Sawhorse Projections are very similar to Newman Projections, but are used more
often because the carbon-carbon bond that is compressed in a Newman Projection
is fully drawn out in a Sawhorse Projection.

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Fischer Projection
The Fischer projection, is a two-dimensional representation of a three-
dimensional organic molecule by projection. The conformation which is drawn in
a Fischer projection of any compound containing more than one stereo centre is
fully eclipsed conformation of the molecule

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Fischer projection to Flying Wedge
OR

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Flying Wedge to Fischer projection

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Inter conversion of Newman Projection to Fischer projection

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Elements of Symmetry
A molecule as a whole is asymmetric or dissymmetric if it does not possess any
element of symmetry such as,
(i) plane of symmetry
(ii) centre of symmetry
(iii) alternating axis of symmetry.
1) Plane of symmetry (mirror plane): It represents the plane bisecting the
molecule such that each half of the molecules is the mirror image of the other
half. For example, tetrafloroethane and tartaric acid

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2) Centre of symmetry (Ci): A molecule is said to have a centre of symmetry
if any line drawn from the centre of the molecule meets identical atoms at
equal distances from the centre. This is also called centre of inversion.
(3) Alternating axis of symmetry: It represents an n-fold axis of symmetry such that
when molecule possessing such an axis is rotated through an angle of 360°/n about
this axis and then reflected across a plane perpendicular to this axis, an identical
structure results. Example chlorofotrm, water etc