Chapter 14. Aromatic Compounds. About The Authors. These PowerPoint Lecture Slides were created and prepared by Professor William Tam and his wife, Dr. Phillis Chang.
These PowerPoint Lecture Slides were created and prepared by Professor William Tam and his wife, Dr. Phillis Chang.
Professor William Tam received his B.Sc. at the University of Hong Kong in 1990 and his Ph.D. at the University of Toronto (Canada) in 1995. He was an NSERC postdoctoral fellow at the Imperial College (UK) and at Harvard University (USA). He joined the Department of Chemistry at the University of Guelph (Ontario, Canada) in 1998 and is currently a Full Professor and Associate Chair in the department. Professor Tam has received several awards in research and teaching, and according to Essential Science Indicators, he is currently ranked as the Top 1% most cited Chemists worldwide. He has published four books and over 80 scientific papers in top international journals such as J. Am. Chem. Soc., Angew. Chem., Org. Lett., and J. Org. Chem.
Dr. Phillis Chang received her B.Sc. at New York University (USA) in 1994, her M.Sc. and Ph.D. in 1997 and 2001 at the University of Guelph (Canada). She lives in Guelph with her husband, William, and their son, Matthew.
In 1834, a German chemist, Eilhardt Mitscherlich, synthesized benzene by heating benzoic acid with calcium oxide
In 19th century, organic compounds were classified as being either aliphaticor aromatic
For other simple and common compounds, the substituent and the benzene ring taken together may form a commonly accepted parent name
When more than two substituents are present and the substituents are different, they are listed in alphabetical order
When a substituent is one that, together with the benzene ring gives a new base name, that substituent is assumed to be in position 1 and the new parent name is used
When the C6H5 group is named as a substituent, it is called a phenyl group
Benzyl is an alternative name for the phenylmethyl group. It is sometimes abbreviated Bn
There is no such equilibrium between benzene ring bond isomers
The Thermodynamic Stabilityof Benzene
6A. The Resonance Explanation of theStructure of Benzene
Hückel’s rule states that planar monocyclic rings with 2, 6, 10, 14 . . . delocalized electrons should be aromatic
Energies of p Molecular Orbitalsin
Monocyclic Systems Based on
The p molecular orbitals that cyclooctatetraene would have if it were planar. Notice that, unlike benzene, this molecule is predicted to have two nonbonding orbitals, and because it has eight p electrons, it would have an unpaired electron in each of the two nonbonding orbitals. Such a system would not be expected to be aromatic.
The bonds of cyclooctatetraene are known to be alternately long and short; X-ray studies indicate that they are 1.48 and 1.34 Å, respectively
7C. NMR Spectroscopy: Evidence forElectron Delocalization inAromatic Compounds
The circulation of p electrons in benzene creates an induced magnetic field that, at the position of the protons, reinforces the applied magnetic field. This reinforcement causes the protons to be strongly deshielded and to have a relatively high frequency (d ~ 7) absorption
pka = 36
pka = 16
One way to evaluate whether a cyclic compound is stabilized by delocalization of p electrons through its ring is to compare it with an open-chain compound having the same number of p electrons
8A. Benzenoid Aromatic Compounds
Nicotinamide adenine dinucleotide, one of the most important coenzymes in biological oxidations and reductions, includes both a pyridine derivative (nicotinamide) and a purine derivative (adenine) in its structure
11A. 1H NMR Spectra
11B. 13C NMR Spectra