Organic chemistry B Chapters 14, 15, 16 Aromatic Compounds By Prof. Dr. Adel M. Awadallah
description
Transcript of Organic chemistry B Chapters 14, 15, 16 Aromatic Compounds By Prof. Dr. Adel M. Awadallah
Organic chemistry B
Chapters 14, 15, 16Aromatic Compounds
By Prof. Dr.Adel M. Awadallah
Islamic University of Gaza
Aromatic CompoundsHydrocarbons (contain only carbon and hydrogen)
a) Saturated: (Contain only single bonds)Alkanes (CnH2N + 2 )
Cycloalkanes (CnH2N )
b) Unsaturated: contain Alkenes: double bonds (,,,CnH2N)
Alkynes: triple bonds ((CnH2N - 2)
Aromatic: benzene like compounds
Facts about double and triple bonds
HH
bond angle 109.5 120 o 180 o
bond length 154 pm 134 pm 121 pm
rotation possible restricted restricted
geometry tetrahedral triagonal planer linear
Hypridization sp3 sp2 sp
Bond Length in Benzene 139 pm (plannar, sp2 hypridized)
Structure of BenzeneBenzene is the parent of a class of especially stable compounds
called aromatic compounds. It was first isolated by Faraday in 1825 from compressed illuminating gas
Different structures were suggested for benzene (C6H6). The regular conjugated hexagon structure was suggested by Kekuli` in 1865
Orbital Model for Benzene
Nomenclature of Aromatic CompoundsCH3
CH3CH3 CH2 OH
OMeOH OCH3 COOH NH2
Br NO2
CH3 CH3
benzene toluene cumene styrene phenol
anisole benzaldehyde acetophenone benzoic acid aniline
bromobenzene nitrobenzene ethyl benzene propylbenzene
Monosubstituted benzenes are named as derivatives of benzene
Disubstituted Benzene
Assigning Priority
• Halogens < alkanes < alkenes < amines < OH < ketone < aldehyde < acid < ester
• Examples
Cl
BrCH3
NO2
CH2
CH3
Cl OH
OH
NO2
NO2
O2N
O CH3
OHOOH
O CH3
OH
OH
m-nitrotoluene m-methylstyrene
CH3
NO2
NO2
O2N
o-bromochlorobenzene (alphabetical order)
p-chlorophenol
2,4,6-trinitrophenol (picric acid)
2,4,6-trinitrotoluene (TNT)
4-hydroxybenzaldehyde 4-acetylbenaldehyde 4-acetylbenzoic acid
Aromatic Compounds in Nature and Health
O
COOH
O
CH3
OH
CHO
OMe
CH3
CH3
CH3 COOHAspirinVanilin
Ibuprofen
Aromatic Character• Aromatic compounds are those that resembles benzene:
• 1) High degree of unsaturation• 2) Do not undergo addition reactions• 3) Undergo electrophilic substitution• 4) Unusual stability• 5) Cyclic five, six, seven• 6) flat or nearly flat molecules• 7) Delocalized pi clouds must contain a total of • (4N + 2) pi electrons [Hueckel 4n+2 rule]• 8) Protons appear around 7 ppm in NMR
Resonance Energy of Benzene
Hetrocyclic Aromatic Compounds
Rearrangement of carbocations
Rearrangement of carbocations
• Reaction of benzene with n-propyl chloride produces isopropyl benzene because of rearrangement
How can you prepare the following compound? Starting from benzene
CH3
COCH3
CH3
NO2
COCH3
BrBr
NO2
start by methylation
start by nitration start by acylationstart by bromination
Reactions of the side chain of alkylbenzene
Arenes: (Alkyl-, Alkenyl- & Alkynylbenzenes)
Resonance structure of the allyl radical
Triphenylmethyl: a stable free radical
Halogenation of the side chain
Alkenylbenzenes: Preparation of styrene
Polycyclic aromatic compoundscigarettes
naphthaline anthracene Phenanthrene
Pyrene benzo[a]pyrenecarcenogenic compound resulting from burning cigarettes
• C60, An aromatic sphere • The Fullerenes