Aromatics
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Describe Benzenes Structure (7 Points)
• Planar -Hexagon (6-Carbon Ring) • Rings of delocalised electrons above and below the planar molecule -120 Degree internal bond angles -All c-c bonds are equal in length -c-c bond lengths are between that of a saturated and unsaturated bond -Each carbon has 3 covalent bonds
What is the most common reaction type for aromatic compounds
Electrophilic substitution of a H for a different compound
what is the shape of benzene?
Planar, Hexagonal. Interior bond angles of 120 degrees
What is the bond length between adjacent C atoms in a benzene ring/
That of between saturated and unsaturated carbon bonds
What happens to the 4th electron in the p orbital of each carbon atom in benzene?
They delocalise Forming Rings of Overlapping pi clouds of electron density above and below the planar molecule
Explain benzenes stability
Rings of electron density above and below the planar makes Benzene very stable. More energy needs to be put into to break it
Draw the skeletal structure of cyclohexa-1,3,5-triene
what is the evidence that benenze is more stable then cyclohexa- 1,2,5 triene
Hydrogenation of cyclohexane = 120kJmol-1 Cyclohexane-1,3,5-triene = -360kJmol-1 Benzene is 152kJmol^-1 more endothermic and therefore more stable As it would take more energy to break its bonds due to the rings of electron density above and below the planar molecule.
why is cyclohexa- 1,2,5 triene not a suitable model for benzene
All bonds wont be at equal length yet benzene is proven to have such quality Would easily undergo addition reactions across the double bonds which benzene wouldn’t
What is the appearance of benzene at 298K
colourless liquid
Why does benzene have a relatively high melting point
Close packing of planar hexagonal molecules when solid
Explain benzenes solubility?
Isn’t soluble in polar solvents as its a non polar molecule
What is benzene not used in schools?
It is a carcinogen
How do you name compounds containing a benzene ring
-Benzene or phenyl-;
Why is Benzene attacked by electrophiles
High electron density above and below the right readily attracted possible;y charged electrophiles
What is seen when benzene is combusted?
Smokey flames due to soot from unhurt carbon From the high C:H ratio within the molecule
Draw a general electrophilic substitution mechanism, for benzene.
Which ion (namer and formula) is used to nitrate benzene>
NO2 + Nitronium Ion
Write the equations for the formation of the the nitronium ion to react with benzene to nitrobenzene
How is the H2SO4 catalyst regenerated in the nitration of benzene
Draw the mechanism for the reaction and general equation for the nitration of benzene
What are the uses of nitrated arenes.
Productions of explosives eg. TNT
How do substituents with a positive inductive effect affect futher substitution in aromatic rings?
They push electrons towards the electron density rings increasing the electron density and making further substitution reactions acts more readily
How does the negative induction effect affect further substitution
They attract electrons away from the electron density rings decreasing the electron density and making further substitution reactions less readily