4.2 aromacity Flashcards
benzene shape and bond angle
Hexagonal planar with 120° bond angles.
C-C Bond Lengths
All C-C bonds in benzene are equal.
benzene bonds are
Benzene has 6 sigma bonds in total.
Pi Bonds
Benzene has 3 delocalized pi bonds.
benzene has a
Sideway overlap of P orbitals forming pi bonds resulting in an electron cloud above and below the plane of carbon . Ring of delocalised electrons so it’s very stable
Why is benzene so stable
Delocalised Electrons spread above and below the plane
Stability of Benzene
Stable due to delocalized electron system.
Addition Reactions
Benzene resists addition to maintain stability.
Electrophilic Substitution
Reactions where electrophiles replace hydrogen in benzene.
Nitration of Benzene
Uses conc HNO3, heated to 50°C.
DINITROBENZENE PRODUCED
if over 50*c then 1-3 dinitrobezene will be produced
Halogenation
Requires a halogen and catalyst for substitution.
Bromination
Involves Br2 and FeBr3 as an anhydrous catalyst.
Friedel-Crafts Alkylation
Alkyl groups added via electrophilic attack on benzene.
Acyl Chlorides
React with benzene in Friedel-Crafts alkylation .
negative inductive effect in benzene
The overlap of the orbitals of the lone pair on the halogen and the delocalised PI system of the benzene increases the bond strength and makes it harder to break and less likely for a reaction to occur
Electronegativity Influence
Decreasing electronegativity affects bond strength.
Negative Inductive Effect
Substituents withdraw electron density from benzene.
Why is benzene susceptible to electrophillic substitution
Benzene is susceptible to electrophilic substitution because of its delocalized π-electron system, which creates a region of high electron density above and below the ring. This makes benzene attractive to electrophiles (electron-pair acceptors).
