3.10 Benzene Flashcards
What are the features of benzenes structure?
Planar structure
Delocalised electrons form pi ring which spreads out electron density
This makes it stable
What is the hydrogenation values which prove kekule wrong?
Cyclohexane= -120
Benzene= -208
1,3,5-cyclohexene= -360
So cannot be the structure of benzene as benzene is more stable
What does the reaction between benzene and bromine suggest about the bonding?
No decolorisation so no double bonds present
What do the bond lengths of benzene tell us?
All the same length between c-c and c=c
What is the equation for the nitration of benzene?
C6H6 +HNO3 - —> C6H5NO2 + H2O
(in exam just draw benzene)
What reaction does benzene undergo and why?
Electrophilic substitution because addition would break delocalised electron system + high electron density which attracts electrophiles
Why is benzene not kept in schools?
Because it is carcinogenic
What are the reagents and conditions for nitration?
Concentrated HNO3 in presence of concentrated H2SO4 with temperature 60 degrees or lower to prevent further substitution
What are the reagents and conditions for reduction of nitrobenzene?
Sn and concentrated HCl which is heated
What are the reagents and conditions for friedel crafts acylation?
Acylchloride in presence of anhydrous AlCl3 heated under reflux
Why in friedel crafts acylation does AlCl3 need to be anhydrous?
Because water is a stronger electrophile and will undergo electrophilic substitution in its place
Why is the nitration of methyl benzene faster than the nitration of benzene?
Methyl group = alkyl groups so alkyl induction which means a greater electron density in the pi ring
