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): nitro ethyl fluoro 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:
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 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.
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. the benzyl group 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 prefixesortho-, 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)
Disubstituted Benzenes meta- (abbreviated m- ) = 1,3-disubstituted (two groups having one unsubstituted carbon between them)
Disubstituted Benzenes para- (abbreviated p- ) = 1,4-disubstituted (two groups on opposite sides of the ring)
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. 4 1 2 3 2 1 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:
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 p-can NOT be used.) • The numbering is carried out to give the substituents the lowest possible numbers. Carbon #1 always has a substituent. • List the substitutents alphabetically with their appropriate #s. 2 1 3 4 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. • The substitutents are listed in alphabetical order. toluene 1 chloro 2 bromo 3 5 4 5-bromo-2-chlorotoluene
Polysubstituted Benzenes 4 1 3 2 3 2 5 1 4 4-bromo-2-ethyl-1-nitrobenzene 5-bromo-2-chlorophenol
Polysubstituted Benzenes 2 1 1 2 3 6 3 6 4 5 5 4 2-bromo-6-chloro-4-nitrotoluene 1-bromo-3-chloro-2-ethyl-5-nitrobenzene
Polycyclic Aromatic Hydrocarbons (PAH) Metabolic byproducts of benzo [a] pyrene react with DNA to form adducts, leading to carcinogenesis (cancer).