3.3.10 - Aromatic Chemistry Flashcards
Benzene
An aromatic compound consisting of a ring of six carbon atoms with six hydrogen atoms and a ring of delocalised electrons
Bond length in the benzene ring
Intermediate length in between that of a double and single bond
Outer electron from the p-orbital of each carbon atom in benzene is…
Delocalised to form the central ring. The ring structure makes benzene very stable compared to other molecules of a similar size
Cyclohexatriene
Three double bonds and three single bonds
Enthalpy of hydrogenation for benzene prediction
-360kJ mol-1, three times the enthalpy change of cyclohexene.
Actual enthalpy of hydrogenation of benzene
-208kJ mol-1, leading to the conclusion of its different, unusual structure
Arenes or aromatic compounds
Compounds that contain benzene as part of their structure
Delocalised ring in benzene
Area of high electron density making it susceptible to attack from electrophiles
Benzene undergoes…
electrophilic substitution
Electrophile to form nitrobenzene
NO2^+ ion
Equation for generation of NO2^+ electrophile
H2SO4 + HNO3 –> H2NO3^+ + HSO4^-
H2NO3^+ –> H2O + NO2^+
Temperature for mono-substitution
55ºc, any greater than this and multiple substitutions occur
Friedel-Crafts acylation
The delocalised electron ring in benzene can also act as a nucleophile, leading to the attack on acyl chlorides
In order for freidel-crafts acylation to take place…
A reactive intermediate must be produced from the acyl chloride and an aluminium chloride catalyst
Equation for the generation of reactive intermediate and catalyst for freidel-crafts acylation
R-COCl + AlCl3 –> R-CO+ + AlCl4-
