Condensed Structural Formula

A molecular formula indicates the number of atoms of each element that are present in a molecule. A structural formula is a graphical representation of a chemical compound that shows the arrangement of atoms as well as chemical bonding around the atoms. A condensed structural formula may also be called a semi-structural formula and is used to describe organic compounds in a line of text. It is illustrated in a single line of text and specifies the atoms in the order that they are located in the molecule. It also shows the functional groups present in the molecule like amine (NH2), alcohol (OH), halogens, and others. It also shows parentheses (round brackets), which indicate the repetition of a group in the chain. For example, the condensed formula of butane is CH₃CH₂CH₂CH₃, and that of 2-chloropropane is (CH₃)₂CHCl.

The subscript number that is written to the right of the final bracket indicates the number of times a group of atoms occurs at that position in the given molecule. Parenthesis (round brackets) is used for enclosing groups attached to a chain when there is a group of atoms attached to a chain. Mostly, covalent bonds are not always shown, but for the sake of clarity, double and/or triple covalent bonds between carbon atoms are usually shown in a condensed structural formula. The same type of atoms that are bonded to one another is always grouped together. When a condensed structural formula is written in a line showing covalent bonds, then it is also called a “linear formula.” Though the condensed structural formula is a useful method for representing simple structures, it tends to be problematic in the case of cyclic compounds.

How to Write Condensed Structural Formula?

Follow the steps mentioned below to write a condensed structural formula or semi-structural formula. Let us discuss them with the help of an example. Write the condensed structural formula of 3-methyl pentane.

Step 1: Draw the 2-dimensional structural formula for the given molecule. 

Here, the given molecule is 3-methyl pentane, so draw its 2-dimensional structural formula.

3-methyl Pentane Structure

Step 2: Identify the carbon skeleton or backbone and check whether the structural formula has any branches or sidechains. Also check functional groups like amine (NH₂), alcohol (OH), halogens, and others.

Identifying Carbon Skeleton

Step 3: From the given structural formula, identify groups of atoms along the carbon backbone. 

Identifying Group of atoms

Here, 3-methyl pentane has five groups of atoms along its backbone, i.e., CH₃, CH₂, CH, CH₂, and CH₃. It also has a branch at the third carbon atom.

Step 4: Now, to write the condensed structure or semi-structural formula of the given molecule, redraw the given formula by replacing the identified groups of atoms in the 2-dimensional structural formula.

2-dimensional structural formula

Step 5: From the backbone or skeleton, remove the single carbon-carbon covalent bonds that are present. (This step is not necessary)

Removing C-C bond

Step 6: When the given molecule has branches or sidechains:

• First, condense the structure as for the carbon backbone

Condensing the structure

• Use parentheses (round brackets) for enclosing groups of atoms that are attached to the chain
  For 3-methyl pentane, there is one CH3 group bonded to the third carbon atom, so we use parentheses to enclose this group of atoms: (CH3)
• Now, use a subscript number to indicate the number of times this group occurs at that position. 
  Here, we have one CH3 group bonded to the third carbon atom, so write it as (CH3).
• Finally, place this group to the right of the carbon atom of the backbone at the position where it is located.
  Write (CH3) to the right of the carbon atom of the backbone at the position where it is located. The condensed structural formula of 3-methyl pentane is CH₃CH₂CH(CH₃)CH₂CH₃.

Uses

• The condensed structural formula helps to show the functional groups of a molecule. The behaviour of compounds can be predicted by knowing the number and type of functional groups as they are responsible for the physical and chemical properties of a molecule.
• It also depicts the geometry of some molecules.
• Furthermore, it plays a significant role in understanding the properties of chemical compounds.

FAQs on Condensed Structural Formula

Question 1: Define the “molecular formula” and give an example.

Answer:

A molecular formula indicates the number of atoms of each element that are present in a molecule. For example, the molecular formula of propane is C₃H₈, i.e., it is made up of three carbon atoms and eight hydrogen atoms.

Question 2: Define the “condensed structural formula” and give an example.

Answer:

A condensed structural formula may also be called a semi-structural formula and is used to describe organic compounds in a line of text. It is illustrated in a single line of text and specifies the atoms in the order that they are located in the molecule. It also shows the functional groups present in the molecule like amine (NH₂), alcohol (OH), halogens, and others. It also shows parentheses, which indicate the repetition of a group in the chain. For example, the condensed formula of butane is CH₃CH₂CH₂CH₃, and that of 2-chloropropane is (CH₃)₂CHCl.

Question 3: The below figure is the structural formula for diethyl ether. Now, determine its condensed structural formula.

Diethyl Ether structure

Answer:

• From the given structural formula of diethyl ether, identify groups of atoms along the carbon backbone, and also identify if it has any branches and functional groups. 
• This molecule has five groups of atoms, along its backbone, i.e., CH₃, CH₂, O, CH₂, and CH₃. 
• Now, to write the condensed structure of the diethyl ether, redraw the given formula by replacing the identified groups of atoms in the 2-dimensional structural formula. 
• Finally, the condensed structural formula of diethyl ether is CH₃CH₂OCH₂CH₃.

Question 4: The below figure is the structural formula for 2-Butanol. Now, determine its condensed structural formula.

2-Butanol structure

Answer:

• From the given structural formula of 2-Butanol, identify groups of atoms along the carbon backbone, and also identify if it has any branches and functional groups. 
• This molecule has four groups of atoms along its backbone, i.e., CH₃, CH₂, CH, and CH₃. There is a hydroxyl group at the second carbon. 
• To write the condensed structure of the diethyl ether, redraw the given formula by replacing the identified groups of atoms in the 2-dimensional structural formula. 
• Now, write the symbol of the hydroxyl group to the right of the carbon atom of the backbone to which it is attached. 
• Finally, the condensed structural formula of 2-Butanol is CH₃CH₂CHOHCH₃.

Question 5: The below figure is the structural formula for 2,2-dimethyl propane. Now, determine its condensed structural formula.

2,2-Dimethyl Propane structure

Answer:

• From the given structural formula of 2,2-dimethyl propane, identify groups of atoms along the carbon backbone, and also identify if it has any branches and functional groups.
• This molecule has three groups of atoms along its backbone, i.e., CH₃, C, and CH₃. To write the condensed structure of 2,2-dimethyl propane, redraw the given formula by replacing the identified groups of atoms in the 2-dimensional structural formula.
• We can see that this molecule has two branches at the second carbon. So, condense the structure for each branch, as for the carbon backbone.
• Use the parentheses to enclose the (CH₃) group of atoms, as we can notice that there are four CH₃ groups bonded to the same carbon atom.
• Now, use a subscript number to indicate the number of times this group occurs at that position. Here, there are four CH₃ groups bonded to the same carbon atom, so write it as (CH₃)₄.
• Write (CH₃)₄ to the right of the carbon atom of the backbone at the position where it is located. 
• Finally, C(CH₃)₄ is the condensed structural formula of 2,2-dimethyl propane.

Question 6: The below figure is the structural formula for 2,3-dimethyl hexane. Now, determine its condensed structural formula.

2,3-Dimethyl Hexane structure

Answer:

• From the given structural formula of 2,3-dimethyl hexane, identify groups of atoms along the carbon backbone, and also identify if it has any branches and functional groups.
• This molecule has six groups of atoms along its backbone, i.e., CH₃, CH, CH, CH₂, CH₂, and CH₃. To write the condensed structure of 2,3-dimethyl hexane, redraw the given formula by replacing the identified groups of atoms in the 2-dimensional structural formula.
• We can see that this molecule has two branches at the second and third carbon atoms. So, condense the structure for each branch, as for the carbon backbone.
• Use the parentheses to enclose the (CH₃) group of atoms, as we notice that one CH₃ group is bonded to the second and third carbon atoms.
• Now, use a subscript number to indicate the number of times this group occurs at that position. Here, we have one CH₃ group bonded to the second and third carbon atoms, so write it as (CH₃).
• Write CH₃ to the right of the carbon atom of the backbone at the position it is located.
• Finally, the condensed structural formula of 2,3-dimethyl hexane is CH₃CH(CH₃)CH(CH₃)(CH₂)₂CH₃.