🧪 Benzene & Its Derivatives | Aromaticity, Structure & Reactions in Organic Chemistry

🧪 Benzene & Its Derivatives | Aromaticity, Structure & Reactions in Organic Chemistry

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  Seminar on Presentingby: Banny S.V BENZENEAND IT’S DERIVATIVES
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   Aromatic compounds:- Aromatichydro carbon compounds are organic compounds composed of carbon and hydrogen atoms, arranged in cyclic structures with delocalized pie electrons Eg:-benzene Benzene and the compounds which resemble benzene in a chemical behaviour known as aromatic compounds.
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  Aromaticity (or)aromatic characters Aromaticitydefined as a property of the conjugated cyclo alkenes which enhances the stability of a molecule due to the delocalization of electrons present in the pie-pie orbitals  The strucutral criteria must be satisfied for a compound to be and an aromatic:
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  Aromaticity (or)aromatic characters 1.Molecule must be cyclic Eg:- Benzene 1,3,5,-hexa tri –ene(non cyclic) 2. Molecule must be conjugated completely Eg:- benzene cyclo hexene
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  Aromaticity (or)aromatic characters 3.Structure must be in planar(pie electron density present above and below the plane) 4.Molecule should satisfy “huckle rule”(4n+2pie electron rule) huckle gave certain rule for defining the aromaticity of organic compounds, the total number of pie electrons in the molecule should be 4n+2 n=integer{0,1,2,3….}
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  Aromaticity (or)aromatic characters Example:- benzeneNaphthalene 4n+2=6 4n+2=10 4n=6-2 n=2 n=1 The molecule which does not satisfy one or more of the above criteria are said to be non aromatic
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  BENZENE AND IT’SSTRUCUTRE  Molecular formula= C6H6  Molecular mass = 78.11gmmole Carbon and hydrogen ratio 1:1 and it consist of 3 conjugated double bonds
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  BENZENE AND IT’SSTRUCUTRE  The structure of benzene can be explained by by following theories.  Kekule’s theory  Resonance theory  Molecular orbital theory
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  Kekule’s theory In 1865,fredrichaugust kekule explain the structure of benzene and proposed that the carbon atoms can join together to form a ring structure. All the c-c bonds are equivalent and hexagonal in shape and each carbon attaches to one hydrogen atom. carbon atoms are joined by – and = bonds and inner circle indicates the valence electrons shared equally by all the 6 carbon atoms Limitation  He fails to explain stability of benzene
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  RESONANCE THEORY  Resonancetheory explains the limitation of kekule theory .this theory proposed that benzene is a resonance hybrid of two kekules (I, II) structures .the two adjacent carbon atoms of the benzene are neither joint by a pure – nor by a pure =. Due to this benzene undergoes resonance {delocalization of pie electrons} to attain more stability
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  bonding frame work
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  Evidences for thestructure of benzene  There are three evidences to prove benzene structure 1. Analytical evidences 2. Synthetic evidences 3. Other evidences
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  Analytical Evidences The analyticalevidences of benzene is carried out by mass spectrometry The IR and UV spectra of benzene indicate that all six c-c bonds are about the same length  based on the NMR spectrum all H atoms appear to be highly deshelled The length bound between C=C and C-C , the molecule being planar, all the C and H atoms lie in a single plane. MOLECULAR FORMULA =C6H6
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  Synthetic evidences  Testfor unsaturation  It confirmed that the benzene is an unsaturated compound, the 3 pie bonds are continuous delocalization and also reveals that benzene is cyclic structure
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  Other evidences  IfBenzene undergoes substitution reaction with chlorine in the presence of FeCl3 it gives chloro benzene
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  Other evidences If benzeneundergoes addition reaction with hydrogen in the presence of catalyst it gives cyclo hexane It confirms that all six hydrogen's are chemically equivalent and the benzene is cyclic in structure
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  REACTIONS OF BENZENE Inbenzene, due to the presence of delocalized pie electrons it makes an electronically rich compound. so that benzene undergoes electrophilic substitution reaction General reaction
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  GENERAL MECHANISM OFREACTION
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  Effect of substituenton reactivity and orientation of mono substituted benzene towards electrophile Nature wise substituent's of two types Electron donate group [EDG] Electron with drawing group [EWG]
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  ELECTRON DONATING GROUP An electron donating group is an atom or group that release electron density to neighbouring atoms from it self and make the neighboring atom electron rich.  Example -NH2,-OH, -R and etc.  Its makes the benzene ring electronically rich at ortho and para positions. Hence electron donating are ortho and para directors
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  Electron withdrawing groups Electron withdrawing group is an atom or group has ability to withdraw electron density from neighboring atoms and make neighbouring atoms are electronically poor  Example:- -CHO,-COR ….etc  Electron withdrawing groups makes the benzene ring electronically deficient, the electron density at meta position are comparatively more than at ortho and para positions. Hence electron withdrawing groups are meta directors