What is a Skeletal Structure?
A skeletal structure, also known as a line-angle formula, is a simplified way of representing organic molecules. In this notation, carbon atoms are implied at the vertices (corners) and endpoints of lines, and hydrogen atoms attached to carbons are not drawn but are assumed to be present to give each carbon a total of four bonds.
Section 2: Key Rules for Interpretation
The fundamental rules for reading skeletal structures are straightforward. Each line represents a covalent bond. The intersection of two lines or the end of any line represents a carbon atom unless another atomic symbol is written. Atoms other than carbon and hydrogen, called heteroatoms (like oxygen or nitrogen), are explicitly shown with their chemical symbols.
Section 3: A Practical Example
Consider the molecule propane (C3H8). Its full structural formula is CH3-CH2-CH3. In a skeletal structure, this is represented by a simple two-segment zigzag line. The two endpoints and the central vertex each represent a carbon atom. The end carbons are assumed to have three hydrogens each, and the central carbon has two, fulfilling the octet rule for each.
Section 4: Why Are Skeletal Structures Used?
Chemists use skeletal structures because they are much quicker and cleaner to draw than full structural formulas. For large, complex molecules like pharmaceuticals or polymers, drawing every atom would be tedious and cluttered. Skeletal structures allow chemists to focus on the carbon backbone and the functional groups, which are the most important parts for chemical reactions.