Formerly used to describe fragrant substances
Now used to refer to the class of compounds that contain six-membered benzene-like rings with three double bonds
14.2. Nomenclature of Benzene Derivatives
Common names are as important as IUPAC names
phenol hydroxybenzene toluene methylbenzene O
aniline aminobenzene O
anisole methoxybenzene O
When two substituents are present, the prefixes ortho, meta, and para (abbreviated o-, m-, and p-) or the numbers are used to indicate the relative positions
When three or more substituents are present, the lowest possible numbers are used to indicate the positions; The substituents are listed alphabetically when writing the name Alkyl substituent smaller than the ring (6 or fewer carbons), named as an alkyl substituted benzene; Alkyl substituent larger than the ring (7 or more carbons), named as a phenyl-substituted alkane
14.3. -14.6. Reactions, Structure, and Stability of Benzene
Benzene is much less reactive than typical alkene and fails to undergo the usual alkene reactions
Benzene reacts only slowly with Br2 and gives the substitution product C6H5Br
All six carbon atoms and all six p orbitals in benzene are equivalent; Benzene is a hybrid of two equivalent forms
Benzene is more stable than the hypothetical 1,3,5cyclohexatriene by 152 kJmol-1; the difference is the resonance energy
14.7. Hückel’s rule: The 4n + 2 p electron rule
Structure must be cyclic with conjugated pi bonds.
Each atom in the ring must have an unhybridized p orbital.
The p orbitals must overlap continuously around the ring.
(usually planar structure)
Compound is more stable than its open-chain counterpart.
If the compound has a continuous ring of overlapping p orbitals and has 4N + 2 electrons, it is aromatic.