Question

What are the rules for writing condensed structural formulas?

Answer 1

Condensed structural formulas are the same as structural formulas, with the only difference that they are written in a single line to save space, making it more convenient and faster to write by grouping similar molecules attached to the same atom.

Complete answer:
Condensed structural formulas are only used to make the structural formulas compact and convenient. There are certain predefined rules to write condensed structural formulas which are as follows:
-We must always write the atoms of the longest chain horizontally in the order in which they are connected.
-We may combine repeating horizontal units in parentheses and adding the number of repeated units in subscript outside parentheses.
-Write all of the ligands (ions that form coordinate bonds with the atom) on an atom immediately to its right, with subscripts for multiple ligands.
-There is an exception for ligands on the leftmost atom as they are to be written immediately to the left of the leftmost atom.
-We should enclose polyatomic ligands in parentheses.
-We can use explicit bonds if needed to clarify attachments like double or triple bonds.
-It is preferable to treat equivalent groups equally.

Note:
While writing structural formulas from condensed structural formulas, we must know the bonding between the atoms or group of atoms, as the condensed structural formula does not show which atom is attached with which atom and with how many bonds if not provided. The number of bonds can be calculated by considering the standard total of bonds each element can make i.e. four for carbon, one for hydrogen, two for oxygen, three for nitrogen etc.