Aromatic Compounds: IUPAC Nomenclature & Benzene Derivatives

• Nomenclature of aromatic compounds involves using trivial (common) and IUPAC (chemical) names
• Monosubstituted benzenes combine names as benzene derivatives

Examples of Monosubstituted Benzenes

• Methylbenzene is commonly known as Toluene
• Ethylbenzene includes an ethyl group
• Isopropyl benzene is commonly known as Cumene
• t-butyl benzene includes a t-butyl group
• Vinylbenzene is commonly known as Styrene
• Halobenzene has a halogen substituent(X=Cl, I, Br, F)
• Nitrobenzene has a NO2 group
• Phenol has an OH group
• Aniline has an NH2 group
• N-methylaniline has a NHCH3 group
• N,N-dimethylaniline has an N(CH3)2 group
• Methoxybenzene is commonly known as Anisole, has an OCH3 group
• Ethoxybenzene is commonly known as Phenetole, has an OCH2CH3 group
• Benzaldehyde has a CHO group
• Acetylbenzene (methylphenylketone/acetophenone) has a COCH3 group
• Benzoylbenzene (diphenylketone/benzophenone) has a COC6H5 group
• Benzoic acid has a COOH group
• Methylbenzoate has a COOCH3 group
• Ethylbenzoate has a COOCH2CH3 group
• Benzene sulfonic acid has a SO3H group
• Benzamide has a CONH2 group
• Acetanilide has a NHCOCH3 group
• Benzanilide has a C6H5NH group
• Anilide refers to an N-phenyl derivative of an acid amide

Nomenclature of Disubstituted Benzenes

• Both the groups and their relative positions are important
• Positional isomers are possible for disubstituted benzenes like xylenes (dimethyl benzenes)
• Adjacent groups (1,2 relation) have the prefix ortho (o).
• Groups separated by one carbon (1,3 relation) have the prefix meta (m)
• Groups on opposite sides of the ring (1,4 relation) have the prefix para (p)
• Naming follows the priority of functional groups, then alphabetical order
• Priority ranking is: COOH > SO3H > CHO > C=O > OH > NH2 > alkyl > NO2 / X
• Alphabetical order is used for nitro and halogen substituents
• Two different substituents are placed in alphabetical order

Common Names for Substituted Benzenes

• If the compound is a derivative of monosubstituted benzene, use the common name for it

Examples:

• o-bromochlorobenzene
• m-nitrobenzoic acid
• p-chlorotoluene
• 1,2-dichlorobenzene (o-dichlorobenzene)
• 1,3-dichlorobenzene (m-dichlorobenzene)
• 1,4-dichlorobenzene (p-dichlorobenzene)
• 2-bromo toluene (o-bromo toluene)
• 3-bromo toluene (m-bromo toluene)
• 4-bromo toluene (p-bromo toluene)
• o-cresol (o-methylphenol)
• m-cresol (m-methylphenol)
• p-cresol (p-methylphenol)
• o-dimethylbenzene (o-xylene)
• m-dimethylbenzene (m-xylene)
• p-dimethylbenzene (p-xylene)
• o-toluidine
• m-toluidine
• p-toluidine
• 4-nitrobenzaldehyde (p-nitrobenzaldehyde)
• 4-hydroxybenzoic acid (p-hydroxybenzoic acid)
• 4-aminobenzaldehyde (p-aminobenzaldehyde)
• 4-formylbenzoic acid (p-formyl benzoic acid)
• 4-nitrobenzaldehyde (p-nitrobenzaldehyde)
• 4-hydroxybenzoic acid (p-hydroxybenzoic acid)
• 4-aminobenzaldehyde (p-aminobenzaldehyde)
• 4-formylbenzoic acid (p-formyl benzoic acid)
• 4-methybenzenesulphonic acid (p-methybenzenesulphonic acid)
• 3-bromoacetophenone (m-bromoacetophenone)
• p-hydroxyacetanilide (Acetaminophen/Panadol)

Nomenclature of Polysubstituted Benzenes

• Number positions if more than two groups are present on the benzene ring
• Ortho, meta, and para designations are not suitable
• Name the molecule as a derivative of a monosubstituted compound if there's a common name, start numbering at the group associated in the common name

Examples

• 1-bromo-2-chloro-4-iodobenzene
• 2,4,6-trinitrophenol (picric acid)
• 3-bromo-5-nitrotoluene

Substituted Anilines

• Substituents on aniline are designated by a number, (o, m, p) if on the ring or N if on the nitrogen.

Examples

• Aniline
• 2-methylaniline (o-methylaniline/o-toluidine)
• 3-ethyl-N-methylaniline (m-ethyl-N-methylaniline)
• N-methylaniline
• N,N-dimethylaniline
• N-ethyl-N-methyl aniline
• N-ethyl-N-methyl-3-methyl aniline
• N-ethyl-N-methyl-4-isopropylaniline

Polynuclear Aromatic Compounds

• Benzene acts as the parent aromatic ring
• Naphthalene, anthracene, and phenanthrene are some of the most common types of fused ring aromatic hydrocarbons
• Numbering systems are important for naming the derivatives of these compounds

Naphthalene

• For monosubstituted naphthalenes, there are two positional isomers
• Isomers are referred to as α- and β-
• Positions 1,4,5,8 are classified as α-positions
• Positions 2,3,6,7 are classified as β-positions
• Numbering begins following fusion

Examples

• alpha-naphthoic acid (Naphthalene-1-carboxylic acid)
• alpha- naphthaldehyde (1-naphthaldehyde/Naphthalene-1-carboxaldehyde)
• Higher priority functional group takes least numbering system if the molecule is disubstituted
• 5-bromonaphthalene-1-carboxylic acid
• 5-bromonaphthalene-2-carboxylic acid
• 1-bromo-5-fluronaphthalene
• 1,4-dibromonaphthalene

Anthracene

• Three positional isomers are present if monosubstituted
• Positions 1,4,5,8 are alpha-substituents
• Positions 2,3,6,7 are beta-substituents
• Positions 9,10 are gamma-substituents

Examples

• 9-chloroanthracene
• 2,7-dibromo-9-hydroxyanthracene

Phenanthrenes

• Three positional isomers are present if monosubstituted
• Positions 1,4,5,8 are alpha substituents
• Positions 2,3,6,7 are beta substituents
• Postions 9,10 are gamma substituents

Examples

• 9-ethylphenanthrene

Aromatic Compounds Designated by Prefixes

• If the substituents on aromatic ring are complex, the aromatic ring is named with a prefix such as phenyl or benzyl

Examples

• p-Benzyl Benzaldehyde
• 4-Phenyl-2-pentene
• 2,4-Dimethyl-2-phenyl pentane
• 1,1-diphenylbuta-1,3-diene
• diphenylether
• 2-benzyl-1,1-dichlorocyclobutane

Reactivity and Orientation in Electrophilic Aromatic Substitution

• Substituents (X) on benzene ring have two effects
• It determines the direction of substitution, this can be either ortho, para or meta
• It also affects the activity and can be either, activators or deactivators of benzene.

Activators

• Activators are groups that cause the SE to occur at a faster rate than benzene
• Activators increase electron density in benzene.

Deactivators

• Deactivators are groups that cause the reaction to be slower than benzene
• Deactivators decrease electron density in benzene.
• O,P-directing groups (e.g. R) are activating groups. O,P-directing groups increase the electron density of benzene ring at o,p- positions
• M-directing groups (e.g. NO2) are deactivating groups. M-directing groups decrease the electron density of the benzene ring at o,p-positions.

Classification of groups

• Activating and o,p-directing groups include strong, moderate and weak activating groups

Strong activating groups

• NH2, -NHR, and NR2
• OH, and -OR
• SH

Moderate activating groups

• NHCOR
• OCOR

Weak activating groups

• R

Important Notes About Activating Groups:

• Activating groups increase the rate of electrophilic substitution
• The group is attached at either ortho, para, or para position
• Atoms having a lone pair attached to the benzene ring will have a Resonance effect, increasing electron distribution at orthro and para
• Activators act as electron donors/releasers which have +M (mesomeric or resonate effect) or +I (inductive effect)
• +M Effect = increases densities on the conjugated system
• -M Effect = Decreases densities on the conjugated system
• +I is responsible for electron donation to a group
• -I is responsible for electrons Withdrawing to a group

Halogens

• Halogens act as deactivators because -I>>>+M
• Halogens act as o,p directing due to + M effect
• The +M effect increases from donating electrons from chlorine to benzene. Therefore requires overlap in carbon 2p with Chlorine 3p orbital
• With Bromide and Iodine, the overlap is effective and carbons 2p overlaps
• Fluorine acts as the most effective o,p-director of halogens

Deactivators vs M-Directors

Deactivators decrease electronic density on benzene using the -M Effect or -I Effect

• M Effect mainly involves atoms that are linked to benzene with a triple of double bind
• I effect mainly involves atoms that have electronegativity
• NO2 , NR3+ , CF3 , CCl3 classifies as a Strong deactivating group ---CN, -SO3H , -COOH,-COOR, -CHO,COR classifies as a Moderate deactivating group CF3 group is strong because the -I effect will help to deactivate benzene

Aromatic Compounds

• Aromatic refers to compounds like benzene in structure
• Molecular formulas are C6H6
• Cyclic compounds are commonly written with a hexagon ring
• Each ring contains a hydrogen bond
• Antiseptic, anesthetics, food preservatives and medication are common uses of aromatic compounds

Benzene & Bonding

• Benzene and its structure allude to its chemical properties
• Benzene is an electron, stable to chemical charges, and resistance
• Benzene will undergo addition reactions
• If reacted with bromine, it leads to catalyst and then turns into substitution
• Hydrogenation energy is 28.6 Kcal energy is released
• 1,3-Cyclohexadine doubles the amount if hydrogenation, as it should
• Hydrogenation produces 49.8 Kcal

Carbon-Carbon Bond Lengths

• They have identical carbons that intermediate in length between normal carbon single and double bonds Therefore the circle of a six side bonds describes all carbon as equivalent
• Benzene with all bonds and singles are very important the way of bookkeeping chemical reactions

Reactivity

• Has a flat six membered ring with a cloud six pei electrons overlapping inside the ring
• Carbon chain is equivalent
• Hydrogen chain is the equivalent
• 120 degree bonds

Aromatic Bond Requirements

• Structure in cyclic form
• Pei electrons are for all aromaticity
• 4n =2

Notes

Aromatic Note

• Structure in cyclic form
• Pei electrons allomaticity -4n =2

Antiaromatic

• Number in ½ are considered aromatic
• They react if they contain cation or antimatter, or electron
• They react when containing any cation

Examples

• Cyclobutadine
• Cyclopentadienyl cation
• Cyclopropenyl anion
• Cycloheptatrienyl anion

Aromatic:

• Non planer’s is Non ARROMTIC
• More stable to escape the flammability

Annulenes

• Compond alternate double binds are called annulenes • Number pei - Is an aunuiles in bracket
• Some anuues are aromatic to the fuel
• (Huckle rules system)

Aromatic:

• They have non planar configuration of planer circle lack of beznene structure

Elctropihilic arromatic reaction

Stable compounds are reaction to chain

• Benzenz ring contains electron structure

Generation of electron

• Accepts to Electrons T system and forms electrons (Slows step) removal proton anion reacts substituted step

Step

2 forms attack Electrophone reacts 2 determine

Nitration

• Electron the structure Electron slow, react to stability

Solfunation

• Generate structure form
• Reacts and generates

Halogen nation

1) Electron and forms
-Two substitutes

2)Determine stability for electrons 3) Protornation

Halogen nation

• React electron • Generate for two substitutes • 3) Generate and for substitutes