CHAPTER 13 – BENZENE & ITS DERIVATIVES AROMATIC COMPOUNDS Originally named because some had nice aromas. Aromatic compounds contain a benzene ring (C6H6). H H H H H H Aliphatics – hydrocarbons not containing a benzene ring (alkanes, alkenes, alkynes). Aromatics are different from aliphatics because do not behave like an unsaturated hydrocarbon (not actually 3 single bonds and 3 double bonds, more like six 1½ bonds between carbons). Bromine does not react with benzene (benzene more stable than double bonded hydrocarbons). Benzene can be represented as: Resonance structure H H H H H H H H H H H H Naming benzene derivatives 1. One group attached to benzene ring: name of group then benzene. i.e. Cl CH2CH3 chlorobenzene CH2CH2CH3 I Common Names of Benzene derivatives CH3 NH2 O C-OH aniline benzoic acid OH toluene phenol 2. Two groups attached to benzene ring: use ortho, meta, para names to identify where groups are attached to ring in place of numbers. (ortho = 1,2; meta = 1,3; para = 1,4) Br Br Br Br Br Br ortho-dibromobenzene meta-dibromobenzene (1,2) (1,3) para-dibromobenzene (1,4) Br CH3 Cl Br 3. Three or more groups attached to benzene ring: use number to identify where groups are attached. Br CH3 Br O2N Br NO2 NO2 1,2,4-tribromobenzene 2,4,6-trinitrotoluene (TNT) Br Br Cl 4. To name the benzene ring as a group, call phenyl, not benzyl. Use phenyl if other functional groups are present phenyl CH2CH3OH 2-phenyl ethanol Polynuclear Aromatic Hydrocarbons (PAHs) – contain 2 or more benzene rings, with each ring sharing 2 carbon atoms. Napthalene Benzopyrene (in cigarette smoke) Carcinogen – a compound that causes cancer PHENOLS -OH attached to aromatic ring OH OH Cl Phenol Lister (1867), discovered phenol solution kills bacteria, used as antiseptic for surgery (no longer used on patients, burns skin) OH C-OCH3 O Methyl salicylate (a non-toxic antiseptic)(oil of wintergreen) Chemical properties of phenols: weak acid; easily oxidized. Phenols used in foods as an antioxidant (prevents food from being oxidized by air). OH OH (CH3)3 C C(CH3)3 C(CH3)3 CH3 O-CH3 BHT BHA (butylated hydroxytoluene) (butylated hydroxyanisole)