Chemistry 2100 Chapter 13

Discovering Aromatics C6H6C6H Å 1.33 Å 1.39 Å

Aromatics

Resonance

Graphene

Carbon Nanotubes

Nomenclature for Arenes Many common names retained PAH

Nomenclature Monosubstituted alkylbenzenes are named as derivatives of benzene; for example, ethylbenzene. The IUPAC system retains certain common names for several of the simpler monosubstituted alkylbenzenes.

Nomenclature –The common names for these monosubstituted benzenes are also retained –Phenyl group (C 6 H 5 - or Ph-): –Phenyl group (C 6 H 5 - or Ph-): The substituent group derived by removal of an H from benzene.

Nomenclature When two substituents occur on a benzene ring, three isomers are possible; they may be located by: –numbering the atoms of the ring or –using the locators ortho (o), meta (m), and para (p).

Aromatic Reactions

Reactions of Benzene By far the most characteristic reaction of aromatic compounds is substitution at a ring carbon. aromatic substitution –This reaction is called aromatic substitution. –Some groups that can be introduced directly on the ring are the halogens, the nitro (-NO 2 ) group, and the sulfonic acid (- SO 3 H) group. Halogenation: 20

Phenols The functional group of a phenol is a hydroxyl ( -OH) group bonded to a benzene ring. –Name substituted phenols either as derivatives of phenol or by common names. 21

Noteworthy Phenols

Phenol Acidity >> acids > thiols ~ phenols > water ~ alcohols Acidity: acids > phenols ~ thiols > water ~ alcohols K a % ionized [ H 3 O + ], M pH ~1  10 7 ~100 ~  10 –  10 –  10 –  10 –  10 –  10 –  10 –  10 – HCl HOAc PhOH EtSH EtOH HOH Comparative acidities of 0.1 M aqueous solutions of representative acids HA 1.8  10 –  10 –

Phenols as Antioxidants Autoxidation

Natural Phenolic Antioxidants Vitamin E  tocopherol) Resveratrol

Man-made Phenolic Antioxidants

Phenols as… Weapons?

"phenethylamine"

ephedrine (ephedra) / pseudoephedrine

methylenedioxymethamphetamine / MDMA / Ecstacy

Organic Food Dye: Carminic Acid

Aromatic Heterocycles nicotine niacin (B 3 ) / nicotinamide thiamine (B 1 ) caffeine (theobromine)

Heterocycles store life’s information (U) T = A