What is a condensed structural formula? How do you draw or write them?
Condensed Structural Formula (Semi-Structural Formula) Tutorial Key Concepts - A molecular formula tells us how many atoms of each element make up the molecule.
- A Lewis (electron dot) structure shows us how the bonding and non-bonding valence electrons are arranged around the atoms.
- A structural formula shows us how the covalent bonds are arranged around the atoms in a molecule.
- A condensed structural formula is a more compact way of drawing the structural formula of a molecule.
- A condensed structural formula is also referred to as a semi-structural formula.
- In a condensed structural formula, or semi-structural formula, covalent bonds are not always shown and atoms of the same type bonded to one another are grouped together.
When the formula is written in a line with covalent bonds shown, it is also referred to as a linear formula. - If there is repetition of a group in a chain, then brackets [square brackets] are used to indicate the repetition of a group in a chain1
A subscript number written to the right of the final bracket tells us how many times this group of atoms is found in this position in the molecule. - If groups of atoms are attached to a chain, then parentheses (round brackets) are used to enclose groups attached to a chain
- For the sake of clarity, double and/or triple covalent bonds between carbon atoms are usually shown in the condensed structural formula, or semi-structural formula.
- To write the condensed structural formula, or semi-structural formula:
Step 1: Draw the 2-dimensional structural formula for the molecule
Step 2: Identify the carbon backbone (or skeleton) and any branches or side-chains in the structural formula as well as any functional groups such as halogen (group 17) atoms.
Step 3: Identify groups of atoms along the carbon backbone in the 2-dimensional structural formula
2-D Structure Condensed Structure H
| H- C - |
H
CH3 H
| - C - |
H
CH2 | - C - |
H
CH | - C - |
C
Step 4: Re-draw the formula by replacing the identified groups of atoms in the 2-dimensional structural formula with their condensed structure, or semi-structural formula.
Step 5: Remove single carbon-carbon covalent bonds from the backbone or skeleton (this step is not absolutely necessary).
Step 6: If the molecule contains branches or side-chains:
(a) condense the structure as for the carbon backbone
(b) use parentheses to enclose groups of atoms attached to the chain
(c) use a subscript number to indicate the number of times this group occurs at that position
(d) write this group to the right of the carbon atom of the backbone at the position it is located.
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