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Introduction of Benzene and Overview
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Introduction of benzene and it's preparation

Rohini chauhan
I am student of chemistry. I did my Bachelor's in chemistry from Delhi University. now I am talking master degree in chemistry. this is real

U
Unacademy user
nice videoes sir but hju thodi deep ma details aapi samjavi sakso??
Amit Shukla
8 months ago
Sure
you are just reading the line.. you are not explaining it properly
mam,voice is not clear
to the point explanation
  1. Benzene Presented by Miss Rohini


  2. Kekule Structure for Benzene In 1865, the ierman chemist August Kekule, proposed a hexagonal ring structure for benzene. The six-membered carboxylic ring consists of three doubled bonds t altcrnatc positions and cach carbon atom is boundcd to a hydrogen atonm


  3. Clau's Structure Armstrong-Bacyer Centric structure CH HC CH CH


  4. By vapour density mcasurcments, Mitscherlich cstabished its molecular f rmula o be CHs He named the substance benin because ol s relation to benzoic acid Aller wards, the name was changcd to benzene the name by which i is known loday in the IUPAC nomenclalure system In 1845, Holinann iso lated benzene form coal tar


  5. ,The unusual stability of benzcnc was demonstra!cd by thc experimental determination benzene and that of cyclohexene ol enthalpy ol hydrogencration ol Enthalpy of hydrogcncnation is the changc in cnthalpy when one mole ol an unsalurated compound is hydrogenated The observed enthlapy of hydrogener of cyclohexene is-19.7 kJ mol-, Pt + H2 AH-119.7 kJ mor1 Cyclohexene Cyclohexane


  6. Thercfore cyclohexa-1,3, tricnc would be cxpccted to be about three tmes tha of cyclohexcnc, thal is. 3x-1197 kJ m359.1 KJmol the enthalpy of hydrogcnation of Pt (expected) Cyclohexa 13,5-triene hypothetical)


  7. Bu the observed ent 208.5 kJ m thalpy of hydrogenation of be nzene is AH-208.5 kJmol1 Benzene Obviously, benzene is more stable han hypothetical cyclohexa - 1.3.5 triene (wth localized double bonds by the ai nount _ 208.5 kJ mol-1-(-3591) kJ, mol-1 = 150.6 kJ mol-1 (36.0 kcal mol-1)


  8. Resonance Structures of Benzene X-ray analysis of crystallin c benzenc has revcalcd some nformation about the gcometry of the molcculc Benzene has a regular hexagonal planar structure Six carbons and six hydrogens are situated in one and the same place Six arbon atoms are siuated at the comers of a regular hexagon. each being connected to a hydrogen. All the carbon, carbon bond lengths are equal and the value is 139 pm. Obviously, the bond length is in between the C-bond length of ethane (154 pm) and thc C bond lcngth of cthylcnc (134pm) All the C-ond lengths arc cqual and the valuc is 109 pm All the C C CandC C bond angles ane 120


  9. To account for the unusual stability, the chemical properties and the geometric parameters cited above the structure of benzene is represcntcd as a resonancc hybrid of the following resonancc contributors Resonancc contributors of benzcnc structurc or Resonance contributors of benzene Resonance hybrid (real benzene)


  10. 120 109 pm 120 139 pm Gcomctric paramcters of benzene molcculc


  11. Preparathion of Benzene Decarboxylation of benzoic acid: Benzene can be prepared in the laboratory by heating sodiu benzoate with soda line COONa+NaOH + Na2CO3 heat Sodium benzoate Benzene Reduction of benzenediazonium chioride: Aniline on trcalment with sodium nitrite benszenediazoniu chloride The late reduction with hvpophosphorous acid or cthanol gives benzenc and dilute hydrochloric acid a 0C yiclds


  12. Trimerisation of acetylene: Acelylenc undcrgocs cyclic trimerisation in thc presence ol nickel cyanide and triphenylphosphine in ether to form benzene along with small amount of cycloocta 1.3.5.7. lctracnc Cu tube 3HC CH Acetylene Ni(CN)2 CeHs)yP, ether 3HC CHr yield) Benzene


  13. Catalytic reforming or aromatization of hexane: Benzene is prepared industrially by heating n hexane under pressure (20 atm) with a mixture of chromium oxide (Cr2O,) and alumina (AI2O a 500-600 C 13 Cr H2C CH2 - H2 Cyclohexane Benzene


  14. Electrophillic Aromatic Substitution Reactions 5 Benzene Electrophile Substitution product elimination step addition ste slow Electrophile complex Substitution product whereH- Resonance hybrid Resonance contributors


  15. , Fluorine (F,) s highly reactive. Monoiluonna tion of benzene is carried out with Agl2 or Xel 2 lodine is unreactive lodination of benzene is caried out with in the presence of an oxidizing agent such as HNO Cucl, These substances accelerate the iodination reaction by oxidiz 2 to a more powerful electrophilic species 2C6H12+ 2HNO3 - 2C^Hsl +2NO2+ 2H20 Benzene Iodobenzene


  16. Mechanism (ieneration of electrophile Nitronium ion Substitution by addition elimination mechanism + H.SO. Nitroniun ion (electrophile) complex Nitrobenzene


  17. Mechanism Generation of electrophile: SO, is the electrophile heat Oleum Substitution by addition - climination mechanism SOj slow fast complex +Hyo