Skeletal Structural Formula (Skeletal Structure or Skeletal Formula) Chemistry Tutorial

Key Concepts

• A skeletal structure may also be referred to as a skeletal structural formula.
• In organic chemistry, a skeletal formula shows just the carbon skeleton (or carbon backbone) and functional groups.
• A skeletal formula does NOT explicitly show

  ⚛ carbon atoms

  ⚛ hydrogen atoms attached directly to carbon atoms

  ⚛ bonds between carbon atoms and hydrogen atoms

• A skeletal formula does explicitly show

  ⚛ bonds between carbon atoms

  ⚛ bonds to functional groups

  ⚛ functional groups

• A skeletal formula is a 2-dimensional (full display) structural formula in which the following have been removed:

  ⚛ carbon atoms

  ⚛ hydrogen atoms attached directly to carbon atoms

  ⚛ bonds between carbon atoms and hydrogen atoms

• Skeletal formula are the most common way for professional Chemists to represent organic (carbon-based) molecules.

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How To Draw and Interpret Skeletal Structural Formula

To draw a skeletal formula:

1. Draw the 2-dimensional (full display) structural formula
2. Identify the carbon skeleton (backbone) and any functional groups present.
3. Remove all the hydrogen atoms (and their bonds) bonded directly to carbon atoms that form the skeleton
   (Do not remove hydrogen atoms that form part of a functional group)
4. Remove all the carbon atoms (but NOT their bonds)
5. You may need to neaten up your skeletal formula by joining the lines up to meet at a point

To draw a 2-dimensional (full display) structural formula given the skeletal formula:

1. Place a carbon atom at the end of each line
   (and/or at the place where two or more lines meet)
2. Add bonds so that each carbon atom makes 4 bonds
3. Add hydrogen atoms to the end of each of these bonds

Drawing a Skeletal Formula Given the 2-dimensional Structural Formula Worked Examples

Example 1: Draw the skeletal formula for butane, molecular formula C₄H₁₀, given the 2-dimensional (full display) structural formula below:

2-dimensional (full display) Structural formula of butane

• Identify the carbon skeleton (backbone) and any functional groups:

  Structural formula of butane minus hydrogens

  Carbon skeleton is shown in red

• From the structural formula above, remove all the hydrogen atoms bonded directly to carbon atoms

  Structural formula of butane minus hydrogens

• From the structure above, remove all the carbon atoms:

  Structural formula of butane minus carbons

• Join all the lines to complete the skeletal formula:

  Skeletal formula of butane

Example 2: Draw the skeletal formula for butan-2-ol (2-butanol), molecular formula C₄H₁₀O, given the 2-dimensional (full display) structural formula below:

Structural formula of butanol

• Identify the carbon skeleton and any functional groups

  Structural formula of butan-2-ol minus hydrogens

  Carbon skeleton is shown in red

  Functional group is shown in blue

• From the structural formula above, remove all the hydrogen atoms bonded directly to carbon atoms
  Note that you do not remove the hydrogen bonded to the oxygen atom as this forms part of the functional group.

  Structural formula of butan-2-ol minus hydrogens

• From the structure above, remove all the carbon atoms:

  Structural formula of butan-2-ol minus carbons

• Join all the lines to complete the skeletal formula:

  Skeletal formula of butane

Drawing the Structural Formula Given the Skeletal Formula

Example 1: Draw the 2-dimensional (full display) structural formula for but-2-ene (2-butene), C₄H₈, given the skeletal formula shown below:

Skeletal formula of 2-butene

• Place a carbon atom at the end of each line (or where two or more lines meet)

  Skeletal formula of 2-butene with carbon atoms

• Add bonds so that each carbon atom makes 4 bonds:

  Skeletal formula of 2-butene with additional bonds

• Place hydrogen atoms at the end of these bonds to complete the structural formula

  Structural formula of 2-butene

Example 2: Draw the 2-dimensional (full display) structural formula for 2-methylpropan-2-ol (2-methyl-2-propanol), molecular formula C₄H₁₀O, given the skeletal formula below:

Skeletal formula for 2-methyl-2-propanol

• Place a carbon atom at the end of each line (or where two or more lines meet)

  Skeletal formula of 2-methyl-2-propanol with carbon atoms

• Add bonds so that each carbon atom makes 4 bonds:

  Skeletal formula of 2-methyl-2-propanol with additional bonds

• Place hydrogen atoms at the end of these bonds to complete the structural formula

  Structural formula of 2-methyl-2-propanol