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Structural Formula

Inorganic compounds are not that many compared to organic compounds and they have simple and straightforward names. Representing them on paper or board is simple. This is because they are mainly a combination of metallic and non metallic components with the exception of certain complex compounds.The naming of complex compounds and their representation is slightly more complicated than the simple compounds. However due to the less number of compounds compared to the organic compounds the naming becomes that much more simpler.
Carbon has a unique property of multiple hybridization and catenation, and forms far too many varieties of compounds which impels a special method in naming. It requires a unique method of representing on paper without any mistakes.The representation of an organic compound is done after estimating the elements present, both the elements and their amounts and proportions. Apart from these the functional groups and their positions are to be ascertained in a written form which is known as structural formula.

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Define Structural Formula

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There are many ways to write the structural formula. The basic requirement to write the formula is to represent properly the elements present in the compound and their positions. Various factors other than just the two dimensional representation to include the spatial representation is also sometimes used to draw a structural formula.

A simple way to represent a compound is to write the number of carbon atoms in one line if the compound is in one line or in required branching. Each valency of carbon is represented by a line. Example n-butane (C4H10) is written as
n butane

  1. When the substituent functional groups and their positions in the molecule are ascertained the hydrogen are replaced with them at the appropriate positions.
  2. In order to make it simple to represent instead of the lines, the elements attached to the carbon atoms are written next to it with each carbon atom separated by a dot. In the above example it is CH3.CH2.CH2.CH3
  3. If there is an element or group or a branch which is other than hydrogen, it will be given in parenthesis. For example: CH3.CH(CH3).CH3 which is iso-butane. CH3.CH(Cl).CH2.CH3 is 2-chlorobutane.
Another way to represent the structure of the compound is to write the stick diagram which is also called the bond line notation. Terminal line if it is single the tip means CH3 and if it is double bond it is CH2 and for triple bond it is CH. Every curve in the structure is one carbon in the chain.

Bond Line Notation

Condensed Structural Formula

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Some of the structural formulas of Organic compounds are given below.

5 Ethyl 2 Methylheptane

2,3 Dimethylbutane- 2,3,3 Trimethylhexane

5,5 Bis 1,2 Dimethylpropyl Nonane

2 Chloro 4 Methylpentane

2 Nitrohex 2 en 4 yne

5 Hydroxyhexanoic

Cyclopentane Cyclohexane

Butylcyclopentane Hexylcyclopentane


1 Cyclopentylbutanol and Phenylcyclohexanol

3 Ethoxy 5 Ethylheptane

Carboxylethyl Pentanedioic Acid

Condensed Structural Formula for Propane

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After ascertaining the contents of an organic molecule by determining the elements present and their percentages, the molecular formula can be arrived. Different tests are there to determine the functional groups. Alkanes have a general formula CnH2n+2.
After counting the number of carbon atoms are arranged in a straight chain unless specified. If there are more than three carbon atoms the isomeric structures also are to be accommodated. Then add the hydrogen so that all the 4 valencies of carbon are satisfied.
Construction of Propane Molecule
and for branched structure of butane any of the given structures.

Different Ways of Writing Isobutane

Alkenes and alkynes are unsaturated. The degree of unsaturation gives us whether it is an alkene or an alkyne. The position of the unsaturation can be established and the formula which is given can then be drawn.

Construction of Isomers of C4H8
Construction of 1-butyne and 2-butyne

The other functional groups such as Halo compounds, carboxylic acids, alcohols etc. the name indicates where the substituent functional group is positioned.
There are three possibilities of these positions- the 1ºcarbon atom( the terminal with 3 hydrogens ) or 2º ( middle with 2 hydrogens) or 3º ( middle with 1 hydrogen). Depending on this one can replace the hydrogens and add the desired functional group.

For example,

The Formulae of Isobutyl and Tert-butyl Chlorides
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