Reactions and Mechanisms of Benzene

Descrição

A2 Chemistry (St Julians work) Slides sobre Reactions and Mechanisms of Benzene, criado por David Morgan em 10-11-2016.
David Morgan
Slides por David Morgan, atualizado more than 1 year ago
David Morgan
Criado por David Morgan mais de 7 anos atrás
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Resumo de Recurso

Slide 1

    Bonding Nitrification Halogenation Friedel-Crafts Alkylation
    Benzene

Slide 2

    Kekule Model
    Kekule assumed that benzene had the bonding of cyclohex-1,3,5-triene (pictured right). However there were isues with this: Measurements from X-Ray diffraction showed equal electron density around the ring All the bond lengths were equal, whereas C=C bonds are shorter than C-C bonds are. The enthalpy of hydrogenation was not simply three times that of cyclohexene. Cyclohexene is -120kJ/mol, expecting Kekule's benzene to be -360kJ/mol, but instead it is -208kJ/mol. Therefore, it was proven that bonding in benzene instead has a ring of delocalised electrons, making it more stable than expected.
    Rubrica: : Kekule's benzene

Slide 3

Slide 4

    Nitration of Benzene
    The electrophile in this reaction is (NO2)+, Nitronium.It is generated by mixing conc sulphuric acid and conc nitric acid and heating to 50 degrees Celcius.
    Rubrica: : Formation of the Nitronium ion

Slide 5

    Halogenation of Benzene
    Benzene reacts with halogens in the same way it does with nitration - electrophilic substitution, however this time, a catalyst is needed, this is called a "Halogen Carrier".If benzene is reacting with Chlorine, traditionally Aluminium Trichloride (AlCl3) is used, and if with Bromine, Iron Tribromide (FeBr3) is used.The reaction takes place at room temperature.

Slide 6

    Friedal-Crafts Alkylation
    This is exactly the same as Halogenation from the previous slide.But instead of a diatomic halogen, there is an alkyl chloride (haloalkane).The entire alkyl group is added on to the benzene ring in the place of the halogen from the slide before.

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