One of the fundamental skills needed in organic chemistry is drawing and interpreting structural formulas, which are used in all parts of organic chemistry. Understanding and converting between Lewis structures, condensed formulas, and bond-line formulas is vital to this skill, as is the ability to recognize, identify, and draw functional groups. Additionally, understanding, identifying, and drawing resonance structures is vital to drawing organic compounds.
At A Glance
- Lewis structures, condensed formulas, and molecular formulas are three ways of representing compounds that are used extensively in chemistry. In organic chemistry, bond-line formulas are the most commonly used structures because they allow for all the information of a Lewis structure or any other structural formula but in a simpler, easier-to-draw manner.
Functional groups are combinations of atoms that have a predictable chemical behavior. Functional groups can be identified by both their structure and their abbreviation, such as COOH for carboxylic acids.
- Alcohols, alkyl halides, amines, and amides are classified as primary (1°), secondary (2°), tertiary (3°), vinyl, aryl, or phenyl.
Resonance structures exist only on paper and are used to understand some of the chemical behaviors of organic molecules. The actual structure is a hybrid of all resonance structures, called the resonance hybrid.
- The basic rules of drawing resonance structures are never break a sigma such as a single bond; move only electrons, never atoms; and never exceed an octet of electrons for second period elements.
Curved arrows are used to show the movement of electrons between resonance structures. The best resonance structures have completely filled octets and the fewest (or no) formal charges, and if there are formal charges, they should be on appropriate atoms (negative on an electronegative atom).