Aromatic Nomenclature Naming substituted benzenes Monosubstituted Benzenes • Most monosubstituted aromatics are named using -benzene as the parent name preceded by the substituent name.
Download ReportTranscript Aromatic Nomenclature Naming substituted benzenes Monosubstituted Benzenes • Most monosubstituted aromatics are named using -benzene as the parent name preceded by the substituent name.
Aromatic Nomenclature Naming substituted benzenes Monosubstituted Benzenes • Most monosubstituted aromatics are named using -benzene as the parent name preceded by the substituent name (as a prefix; all one word): fluoro nitro ethyl F NO2 CH2CH3 fluorobenzene nitrobenzene ethylbenzene Alkyl-substituted Benzenes • Alkyl substituted benzenes are named according to the length of the carbon chain of the alkyl group. • With six carbons or fewer in the alkyl chain, they are named as ‘alkylbenzene.’ • e.g., propylbenzene: CH2CH2CH3 Alkyl-substituted Benzenes • With more than six carbons in the alkyl chain, they are named as a ‘phenylalkane,’ where the benzene ring is named as a substituent (phenyl) on the alkane chain • e.g., 4-phenylnonane CH3CH2CH2 CH2CH2CH3 CHCH2CH2CH2CH2CH3 = CHCH2CH2CH2CH2CH3 CH3CH2CH2CHCH2CH2CH2CH2CH3 4-phenylnonane Common Names of Subs. Benzenes • There are a number of nonsystematic (common) names commonly used for certain monosubstituted benzenes (see next slide) • These ten common names should be memorized. • These common names are used as base names when naming more their more highly substituted derivatives. Examples of these will be given later. Common Names of Subs. Benzenes CH3 tolue ne O anis ole C O C H be nzalde hyde be nzonitrile CH2 s tyre ne O C OH be nzoic acid C N aniline H phenol OCH3 C NH2 OH CH3 CHCH3 cum e ne CH3 acetophe none The Benzyl Group • The benzyl group is a common name for a methyl substituted benzene (toluene) having substitution for one of the hydrogens on the methyl group. CH2 the benzyl group CH2Br CH2Br CH2OH benzyl bromide benzyl alcohol Disubstituted Benzenes • Disubstituted benzenes can be named in one of two ways. Each method describes the relative positions of the two groups on the benzene ring. • Systematic numbering of the aromatic ring. • Using the prefixes ortho-, meta-, or para-. • When numbering the ring carbons, carbon # 1 is always a substituted carbon. • The substituents are listed alphabetically. Disubstituted Benzenes ortho- (abbreviated o- ) = 1,2-disubstituted (two groups on adjacent carbons on the ring) F F CH2CH3 Br o-difluorobe nze ne or 1,2-difluorobe nze ne o-brom oe thylbe nze ne or 1-brom o-2-e thylbe nze ne Disubstituted Benzenes meta- (abbreviated m- ) = 1,3-disubstituted (two groups having one unsubstituted carbon between them) Br Br m-dibrom obe nze ne or 1,3-dibrom obe nze ne Br NO2 m-brom onitrobe nze ne or 1-brom o-3-nitrobe nze ne Disubstituted Benzenes para- (abbreviated p- ) = 1,4-disubstituted (two groups on opposite sides of the ring) Br Cl Cl p-dichlorobe nze ne or 1,4-dichlorobenze ne Cl p-brom ochlorobenzene or 1-brom o-4-chlorobenze ne Disubstituted Benzenes • When one of the substituents changes the base name, either o-, m-, and p- or numbers may be used to indicate the position of the other substituent. • Carbon # 1 is always the carbon bearing the substituent that changes the base name. Br 4 1 OH 3 1 2 Cl 2 NH2 p-bromoaniline or 4-bromoaniline o-chlorophenol or 2-chlorophenol Common Names of Disubs. Benzenes • There are a few nonsystematic (common) names for disubstituted benzenes that you should be familiar with: CH3 CH3 CH3 o-xyle ne CH3 CH3 CH3 m -xyle ne CH3 p-xyle ne CH3 OH o-cre s ol CH3 OH m -cre s ol OH p-cre s ol Polysubstituted Benzenes • Polysubstituted benzenes must be named by numbering the position of each substituent on the ring (with more than two substituents, o-, m-, and pcan NOT be used.) • The numbering is carried out to give the substituents the lowest possible numbers. Carbon #1 always has a substituent. CH2CH3 • List the substitutents 2 F 1 3 alphabetically with 4 their appropriate #s. NO2 2-ethyl-1-fluoro-4-nitrobenzene Polysubstituted Aromatics having a Common base name • Common names of the monosubstituted benzenes are used as parent names for polysubstituted aromatics when one of the substituents changes the base name. • For such rings with common names, the carbon bearing the substituent responsible for the common name is always carbon #1. toluene CH3 • The substitutents are 1 Cl chloro listed in alphabetical 2 order. bromo Br 5 3 4 5-bromo-2-chlorotoluene Polysubstituted Benzenes Br OH 4 1 1 3 2 CH2CH3 NO2 4-bromo-2-ethyl-1-nitrobenzene Cl 2 Br 5 3 4 5-bromo-2-chlorophenol Polysubstituted Benzenes Br 2 3 O2N 4 Br 1 CH3 6 5 6 Cl 2-bromo-6-chloro-4-nitrotoluene O2N 5 1 2 CH2CH3 3 4 Cl 1-bromo-3-chloro-2-ethyl-5-nitrobenzene Polycyclic Aromatic Hydrocarbons (PAH) anthracene naphthalene phenanthrene pyrene benzo [a] pyrene Metabolic byproducts of benzo [a] pyrene react with DNA to form adducts, leading to carcinogenesis (cancer).