aromatic chemistry

Question 1

benzene

Answer 1

6 carbon structure with a delocalised ring
-each carbon atom joined to 2 hydrogen atoms
-aromatic hydrocarbon

Question 2

kekule model

Answer 2

ring of 6 carbon atoms with alternating double and single carbon bonds

Question 3

disprove kekule model

Answer 3

if benzene contained double carbon bonds it would decolourise bromine- but it doesnt
-benzene also does not undergo electrophilic reactions
Also kekule structure would be expected to have an enthalpy change of of hydrogenation that is 3 times that of cyclohexene

Question 4

naming aromatic compounds

Answer 4

short prefix if alkyl, halogens or nitro groups are added
ethyl,chloro.nitro

Question 5

delocalised model of benzene

Answer 5

each carbon atom has one electron in p-orbital at right angles to the plane of the bonded carbon and hydrogen bonds
-the overlapping of p-orbitals creates a system of pi bonds which spread over all six of the carbon atoms in the rings structure

Question 6

friedel crafts reactions

Answer 6

acylation and alkylation

Question 7

nitrating benzene

Answer 7

HNO3 + H2SO4 –> NO2 + + HSO4 - +H20 (generating electrophile)
H+ + HSO4- –> H2SO4
-mechanism
(regenerating catalyst)

Question 8

alkylation of benzene

Answer 8

adding alkyl group (halogen carrier)
CH3Cl + AlCl3 –> CH3+ AlCl4 - (generating electrophile)
-mechanism
H+ + AlCl4- –> AlCl3 +HCl

Question 9

halogenation of benzene

Answer 9

Br2 + AlBr3 –> AlBr4 - + Br+ (generate electrophile)
-mechanism
H+ + AlBr4 - –> AlBr3 + HBr

Question 10

naming acyl chlorides

Answer 10

longest carbon chain + ‘oyl chloride’

Question 11

acylation of benzene

Answer 11

CH3COCl + AlCl3 –> CH3CO+ + AlCl4 -
-mechanism COCH3
AlCl4- + H+ –> AlCl3 + HCl
phenyl ethanoate eg
-phenyl + carbon chain(oate)

Question 12

phenol

Answer 12

when the OH is directly bonded to the benzene
uses:
-antiseptics
-alkyl phenols-detergents
-salicylic acid- painkillers

Question 13

Bromination of phenol

Answer 13

reacts instantly with phenol with NO catalyst and room temp
phenol + 3Br2 with substitute 3 times at 2,4,6
(white ppt)

Question 14

reactivity of phenol

Answer 14

lone pairs on OH group are in p-orbitals
increases electron density
allows ring to induce dipole across halogens

Question 15

2,4 directing groups

Answer 15

electron donating
eg NH2,OH,F,Cl
increase electron density
easier to react

Question 16

3,5 directing groups

Answer 16

electron accepting
eg COOH,NO2
less electron density
harder to react

Question 17

naming directing groups

Answer 17

ortho- carbon 2
meta- carbon 3
para- carbon 4

Question 18

testing for alcohols

Answer 18

add acidified k2Cr2O7
orange to green

Question 19

Testing for aldehyde

Answer 19

Tollens reagent
-silver nitrate
-sodium hydroxide (brown ppt)
-dilute ammonia (colourless)
Silver mirror positive

Question 20

Testing for carbonyls (aldehyde or ketone)

Answer 20

Brady’s reagent
-2,4 DNP
-sulfuric acid
-methanol
Orange/yellow ppt