6.1.1 Aromatic compounds
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molecular formualar of benzene
C6H6
what mechanism does benzene undergo
electrophillic substitution
how many bond lengths would benzene have to fit with kekule
2 different bond lengths due to double and single bonds
how many bond lengths does benzene actually have
one
what explains the anomalous properties of benzene
a ring structure where the spare pairs of electrons are delocalised around all 6 carbon atoms - delocalised electrons above and below the plane of atoms
bonding in benzene
each C has 4 outer electrons 1 used to bond to H 2 used to bond to adjacent carbons remaining 6 are delocalised in a cloud above and below the plane of the ring
what do the delocalised electrons in benzene cause
rise to extra stability called delocalisation energy
isomer of arene compound for benzene
if had 3 double bonds it should have 2 isomers but benzene only has one
enthalpy of hydrogenation for kekule structure to prove its wrong
it should undergo similar reactions to cyclohexene and cyclodihexene howeveer it doesnt as the enthalpy is lower
Halogenation of benzene
halogen carrier must be present - FeCl3,AlBr3,FeBr3
nitration of benzene
concentrated nitric acid with concentrated sulphuric acid - warm
alkylation of benzene
reacting benzene with haloalkane with presence of AlCl3
acylation of benzene
presence of AlCl3
Directing effect
presence of substituted groups on a benzene ring will have an effect on the substitution of further groups
what increase the electron density
releasing electrons
what decreases the electron density
withdrawing electrons
electron donating groups
-OH phenol -NH2 amine
electron withdrawing groups
• NO2 nitro
activating groups
side chains that increase electron density allow electrophiles to react faster than with benzene
what directing numbers are electron donating groups
2,4
oxygen as a donating group and how it happens
O is very electronegative has effect of pushing electrons forcing areas of charge over the 2,4,6 position causing negative dipoles that attract electrophiles more effectively
deactivating groups
side chains that decrease electron density slow electrophile reactions compared to benzene
NO2 directing numbers
3,5