Structural Representation Of Organic Compounds

Complete and Condensed Formulae

Each pair of electron making a covalent bond is represented by a dash (—).

Two dashes represent a double bond and three dashes represent a triple bond.

Such structural representation are called complete structural formulae or graphic or displayed formulae.

These structural formulae can be further condensed by enclosing the repetitive structural unit within a bracket and placing an integer as a subscript indicating the number times the structural unit gets repeated.

For Ex :CH₃CH₂CH₂CH₂CH₂CH₂CH₃ can be condensed to CH₃(CH₂)₅CH₃

CH₃CH₂CH₂CH₂CH₂CH₂CH₂COOH can be condensed to CH₃(CH₂)₆COOH

 

Bond-Line structural Formulae

1) It is a simple , short and convenient method of representing organic molecule.

2) Carbon-carbon bonds are shown by lines drawn in a zig-zag fashion and carbon atoms by line ends  and intersection.

3)A single bond is represented by a single line , a double bond by 2 parallel lines and a triple bond by three parallel lines.

4)  Carbon atoms are not shown but all atoms other than carbon and hydrogen atoms such as oxygen, nitrogen, halogen are shown on zig-zag line.

5) Each carbon on the line end or intersection is attached to required number of hydrogen atoms i.e. terminal denote CH₃ group and an unsubstituted intersection denotes a CH₂ group.

For Ex: butyl chloride

3-methyl pentane

Polygon formulae

There are many organic compounds ,in which carbon atoms are not joined in a chain but are joined in a ring.These are called cyclic compounds and are usually represented by polygon without showing carbon and hydrogen atoms.

The corners of a polygon represent a carbon atom and the sides of a polygon denote a carbon-carbon bond.

If an atom or a group of atoms other than hydrogen is attached to carbon, then that atom or a group of atoms is shown in this structure.

For Ex: Cyclopropane

Cyclobutane

Cyclopentane

Cyclohexane

chlorocyclohexane

 

Three-Dimensional (3-D) representation of organic compounds

1) The three-dimensional structure of organic compound can be represented on paper by using certain conventions.

2)  By using solid and dashed wedge formula, 3-D image of a molecule from a two-dimensional picture can be perceived.

3) The thick solid line or the solid wedge indicates a bond lying above the plane of the paper and projecting towards the observer.

4) A dashed wedge is used to represent a bond lying below the plane of paper and projecting away from the observer.

5) Wedges are used in such a way that the broad end is towards the observer.The bond lying in the plane of paper are depicted by using a normal or an ordinary line.

A representation which completely describes the actual positions of various atoms of a molecule in space is called a spatial formulae or three-dimensional i.e. 3-D structure.