Organic Chemistry Reviews Chapter 14 Cindy Boulton March 22, 2009
Aromatic Compounds Benzene 6 member ring 6 π electrons Alternating Double Bonds Resonance Hybrid All bonds 1 ½ - same length Only as many Hydrogen Atoms as Carbon Atoms
Nomenclature of Benzene Derivatives Disubstituted Benzene Ortho: 1,2 Meta: 1,3 Para: 1,4 Phenyl group name of a benzene attached to a parent chain Toluene Benzene with one methyl group attached Xylene Benzene with two methyl groups attached Ortho, meta, or para Phenol Benzene with a hydroxyl group attached (-OH) Alcohol
Nomenclature of Benzene Derivatives Aniline Benzene with a amine group attached (-NH 2 ) Anisole Benzene with an ether bond to a methyl group Phenly-O-Methyl Acetophenone Benzene with an acetyl group attached Phenyl-(C=O)-Methyl Benzaldehyde: formyl group attached, Phenyl-(C=O)-H Oil of bitter almond Benzophenone: two benzene rings attached, Phenyl-(C=O)- Phenyl
Nomenclature of Benzene Derivatives Benzoic Acid Benzene with a carboxyl group attached, Phenyl-(C=O)-OH Benzenesulfonic Acid Benzene with HSO 3 attached Nitrobenzene Benzene with nitrite attached (-NO 2 )
Stability of Benzene Stability of conjugate π systems Pseudo π bond is formed Some of the π electron density is delocalized The π bond is spread out and becomes harder to react More stable Stability of aromatic compounds Resonance stabilizaion Forms a resonance hybrid Delocalization of electrons by molecular orbitals The π bond electrons are completely delocalized
Aromatic Compounds Aromatic Rules 1) Cyclic 2) Planar P-orbitals have to line up to from π bonds 3) A Huckle Number of Delocalizable electrons Huckle Number = 6,10,14,18,… All sp 2 Carbons and alternating double bonds Annulene Benzene = [6] annulene Benzoid Polycyclic aromatic 6-member rings fused together Non-Benzoid Polycyclic aromatic Non 6-member rings fused together (=12)
Heteroatomic Aromatics Not Carbon Follow Aromatic Rules: Cyclic Planar Delocalizable electrons (Huckle Number) Lone pair Can be planar, perpendicular to ring, with other electrons to be counted as delocalizable electrons Can be non-planar, not perpendicular, and not delocalizable depending on geometry of molecule Pyridine, Furan, Pyrole, Thiophene
Aromatic Compounds with Charge 5-Carbon ring 4 delocalizable electrons + Electron pair = 6 delocalizable electrons Negative Charge 7-Carbon ring 6 delocalizable electrons + vacant orbital = 6 delocalizable elcetrons Positive Charge