# Benzene and Aromaticity

## Vocabulary

### annulene

any of a class of completely conjugated cyclic hydrocarbons (such as benzene or cyclooctatetraene) that are monocyclic

### antiaromatic

molecule that is cyclic, has a continuous circle of p orbitals, has planar geometry, and does not have a Hückel number of electrons but instead has [4n] $\pi$ electrons

### aromatic

molecule that is cyclic, has a continuous circle of p orbitals, has planar geometry, and has a Hückel number ($4n+2$) of $\pi$ electrons

### benzene

cyclic aromatic molecule with the chemical formula C6H6

### derivative

compound that is derived from a similar compound by a chemical reaction

### disubstituted derivative

derivative of benzene with two substituents

### Frost circles

method to predict bonding $\pi$ molecular orbitals, which indicate aromaticity

### Hückel's rule

rule that states that the number of delocalized electrons in the $\pi$ cloud in an aromatic ring is equal to [$4n+2$], where n is zero or a positive integer

### heterocyclic

any molecule relating to, characterized by, or being a ring composed of atoms of more than one kind

### infrared (IR) spectroscopy

method that observes the vibrations of bonds and provides evidence of the functional groups present

### meta

prefix that indicates there is one carbon atom between the carbon atoms that have the substituents, producing a 1,3-disubstituted benzene pattern

### molecular orbital theory

solution of the Schrödinger equation that describes the probable location of an electron relative to the nuclei in a molecule and so indicates the nature of any bond in which the electron is involved

### monosubstituted derivative

derivative of benzene with only one substituent

### nonaromatic

molecule is not cyclic or planar or does not have a continuous circle of p orbitals

### ortho

prefix that indicates there are no carbon atoms between the carbon atoms that have the substituents, producing a 1,2-disubstituted benzene pattern

### para

prefix that indicates there are two carbon atoms between the carbon atoms that have the substituents, producing a 1,4-disubstituted benzene pattern

### polycyclic

refers to molecules with more than one ring structure

### polycyclic aromatic compound

compound that has more than one ring structure and is aromatic

### polysubstituted derivative

benzene with more than two substituents

### resonance

method that organic chemists use to depict the Lewis structures of organic molecules where electrons can be in two or more different places around fixed atoms