What is a Condensed Structural Formula?
The condensed structural formula provides the shortest way to understand the atoms and their numbers, their connection with respect to each other, and therefore, visualize the compounds' structure without elaborately drawing it, but by writing it in a single line.
So, if the elaborate structure of butanoic acid look like A, the condensed structural formula would look like B.
A molecular formula C would look even smaller but won’t show any connection between the atoms, only representing which atoms are present.
So, the atoms and their joining pattern are listed in a single line in the condensed structural formula. The carbon chain is the backbone, and all the attached hydrogen atoms are usually written immediately after it.
For example, butane (C4H10) is written in the condensed formula as - CH3CH2CH2CH3.
If other heteroatoms are present, it gets the third priority after the carbon and the hydrogen.
For example, 2-chlorobutane is represented as CH3CHClCH2CH3.
The principal function group is written along with the parent carbon chain. In case of any additional functional group or a substituent, like NO2, OH, COOH, etc., it is expressed in parenthesis.
For example, 3-hydroxybutanoic acid is expressed as CH3CH(OH)CH2COOH or CH3CH(OH)CH2CO2H. The carboxylic functional group is part of the main carbon chain; however, the substituent is -OH at the 3rd carbon’s position, enclosed within parenthesis.
Sometimes, these structural formulae are further condensed by enclosing the repetitive structural unit within a bracket and placing an integer as a subscript indicating the number of times the structural unit gets repeated. For example, CH3CH2CH2CH2CH2CH2CH2CH3 can be condensed as CH3(CH2)6CH3.
The dash (-) for a single bond is usually omitted; however, the double (=) and triple (≡) bonds for alkenes and alkynes are sometimes expressed.
The propene in the condensed structural formula is written as CH2=CHCH3. Acetonitrile is CH3CN or CH3C≡N.
The terminal group on the left is sometimes inverted to highlight the atom attached to the main carbon chain.
For example, CH3CH2CH2CH3 may be written as H3CCH2CH2CH3. Other examples are- HOCH2CH2CH3 instead of OHCH2CH2CH3 (Oxygen forms a bond with the carbon chain) or N≡CCH(OH)CN in place of C≡NCH(OH)CN (carbon of C≡N forms a bond with the carbon chain).
Nonbonding electrons are rarely shown in the condensed structural formulas.
The condensed structures are assumed to follow the octet rule even if the condensed notations do not show bonding.
More Examples on writing condensed structural formula-
Draw the Condensed Structural formulae of the following organic compounds.
Hint- First, condense the terminal and central hydrogens. Use a dash to connect the main carbon chain and attach the substituents. In the final step for writing the condensed formula, remove the dashes and keep the central substituents not part of the parent chain within brackets.
1) 3-methyl pentane
2) 2-(aminomethyl)ethanoic acid
3) 1-chloro-3-methoxybutane
4) Diethyl ether
