aromatic compounds

Question 1

name given to family if chemicals that benzene belongs to?

Answer 1

arenes

Question 2

Kekele structure

Answer 2

cyclohex w 3 db

Question 3

proof of delocalised pi bond

Answer 3

• unable to undergo electrophilic addition
• in x ray christollography, all bonds are the samel length.
• hydrogenation energy lower than expected
• one positional structural isomers of 1,2 dichlorobenze

Question 4

explain the lack of isomers (to disprove kekule)

Answer 4

If benzene was a triene with alternate C-C and C=C bonds, then
some molecules would have a double bond and some molecules would not in 1,2 dichlorobemzene. different positional structural isomers of 1,2 dichlorobenzene.

Question 5

explain the wierd hydrogenation enthalpy of benzene

Answer 5

the hydrogenation enthalpy of benzene is less exothermic.

More energy required to break delocalised pi bond than released when bonds with hydrogen form.

Benzene simply more stable.

Question 6

electrophilic substitution of benzene

Answer 6

• nitration of benzene
• alkylation of benzene
• halogenation of benzene
• acylation of benzene

Question 7

what electrophile do we add in nitration?

Answer 7

NO2+

Question 8

what electrophile do we add in alkylation

Answer 8

a carbocation (e.g CH4 +)

Question 9

what electrophile do we add in acylation?

Answer 9

CH3CO+ to form an aromatic keytone

Question 10

In the nitration of benzene, above…. Celsius … will occur

Answer 10

50 degrees, further substitution

Question 11

acetylation of benzene and conditions

Answer 11

makes an aromatic keytone
(acyl chlorides are used with general formula of R-COCl)
conditions- halogen carrier

Question 12

phenol dissociates into…

Answer 12

a phenoxide ion and a proton

Question 13

phenol dissociates into…

Answer 13

a phenoxide ion and a proton

Question 14

phenol vs carboxylic acid

Answer 14

phrnol reacts only with strong bases. carboxylic acids react with weak bases like carbonates as well, producing effevescence

Question 15

electron donators… the delocalised pi bond

Answer 15

activate

Question 16

explain delocalised pi bond in benzene

Answer 16

p orbitols overlapp sideways above and below benzene. 3 electrons shared above and below (delocalised ring of electron density).

Question 17

when a benzene ring has 1 substituent that his a halogen, nitro or small alkyl group, its called?

Answer 17

prefix…benzene
e.g nitrobenzene

Question 18

when benzene is attatched to an alkyl group of 7 or above carbon atoms?

Answer 18

phenyl- prefix

Question 19

benxene with carboxyl group

Answer 19

benzoic acid

Question 20

benzene plus amine group

Answer 20

phenylamine

Question 21

benzene plus aldehyde group

Answer 21

benzaldehyde

Question 22

phenol + bromine water

Answer 22

• electrophilic substitution
• bromine decolorised
• ppt forms
• smell of antiseptic
• 2,4,6 tribromophenol

Question 23

temperature of Friedel-crafts acylation?

Answer 23

60 degrees

Question 24

temperature of nitration of benzene

Answer 24

50 degrees, above 50 degrees, further substitutions occur.

Question 25

2 isomers produced when phenol reacts with nitric acid?

Answer 25

2nitro phenol, 4 nitro phenol

Question 26

how does activation and deactivation affect substitution of groups?

Answer 26

activated groups- reacts more readily, can produce a multisubstituted product.

Deactivated groups- react less readily, produce usually only a monosubstituted product.

Question 27

What is the name of the electrophile N02+?

Answer 27

nitronium ion

Question 28

3,5 directing, electron withdrawing examples?

Answer 28

-CHO
-NO2
- COOH
-CN

Question 29

2,4,6 directing, electron donating examples?

Answer 29

• OH
  -NH2
• I, Cl,F