10O- Aromatic Chem

Question 1

What’s the molecular formula for benzene

Answer 1

C6H6
Hexagon with a circle inside

Question 2

Bonding and structure of benzene

Answer 2

Each C atom is bonded to two other C atoms and a H atom by single covalent bonds
There is 1 unused electron on each C atom in the p orbital, 6 delocalised electrons are in a ring structure above and below the plane of carbon atoms

Question 3

What is the shape of a benzene molecule and bond length

Answer 3

Planar
Same C-C bond length between that of a single C-C bond and a double C=C bond due to

Question 4

Why does benzene prefer substitution reactions over addition

Answer 4

Addition reactions would involve breaking apart the the delocalised system
Most reactions involve substitution of hydrogen, benzene has a high electron density so attracts electrophiles, usually reacts through electrophilic substitution

Question 5

What mechanism is benzene involved in

Answer 5

Electrophilic substitution

Question 6

What’s nitration used for

Answer 6

A step in the synthesis of explosives and amines

Question 7

Equation for generating a nitronium ion (nitration) NO2+

Answer 7

HNO3 + 2H2SO4 —> NO2+ + 2HSO4- + H3O+

Question 8

Electrophillic substitution mechanism (nitration)

Answer 8

1. Arrow from benzene ring onto nitronium ion
2. Benzene ring is only partial it should be drawn further than the sub group and the two carbon atoms either side.
   +ve charge inside benzene ring, arrow from C-H bond into ring
3. Draw benzene with sub group on it

Question 9

Equation for friedel crafts acylation

Answer 9

AlCl3 + R-COCl —> AlCl4- + R-CO+

R is the alkyl group, rest of the acyl chloride depending on which it is

Question 10

Naming benzene

Answer 10

1 sub group- name of sub group/molecule, benzene eg chlorobenzene
If a carboxyl or aldehyde group is present they take priority taking the suffix eg benzaldehyde

2 or more sub groups- same priority rule as naming chains, use lowest numbers, name in alphabetical order
eg 2-methyl-1,3,5-trinitrobenzene
Aldehydes and carboxylic acids take priority and have root name

Benzene regarded as sub group C6H5 group is phenyl group, used if attached to amines, alkenes, middle of alkane chain, ketone, ester
eg phenylamine