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Skeletal Formula Tutorial

Key Concepts

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 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.

Drawing and Interpreting Skeletal Formula

To draw a skeletal formula:

  1. Draw the 2-dimensional 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 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

Example: Drawing a Skeletal Formula

Draw a skeletal formula for propane, molecular formula C3H8

  1. Draw the structural formula
    H
    |
    H H- C -H H
    \ / | \ /
    H-C H C-H
    / \
    HH

  2. Identify the carbon skeleton (backbone) and any functional groups present.
    H
    |
    H H- C -H H
    \ / | \ /
    H-C H C-H
    / \
    HH

    Carbon skeleton shown in red
    No functional groups are 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)
    C
    / \
    C C

  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

Drawing a Structural Formula

Draw the structural formula give this skeletal formula:

  1. Place a carbon atom at the end of each line
    (and/or at the place where two or more lines meet)
    O
    ||
    C C H
    \ / \ /
    C O

  2. Add bonds so that each carbon atom makes 4 bonds
    O
    | ||
    -C C H
    | \ / \ /
    C O
    / \

  3. Add hydrogen atoms to the end of each of these bonds to complete the structural formula
    H O
    | ||
    H-C C H
    | \ / \ /
    H C O
    / \
    H H


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