Topic 18 Organic III

Question 1

What did Kekule suggest the benzene structure to look like?

Answer 1

Cyclohexa1,3,5-triene

Question 2

How was Kekule’s benzene structure suggestion proved/disproved?

Answer 2

Supported by
- very sooty after combusting (due to low C:H ratio)
Disproved by
- bromine water does not react, so no C=C bonds
- regular bond lengths
- enthalpy of hydration values

Question 3

What are chemical evidences for the structure of benzene?

Answer 3

1. Bromine water doesn’t decolourise, so no C=C present
2. X-ray crystallography, equal bond lengths so same bonds between each C
3. Enthalpy of hydration data - much lower than expected

Question 4

What do you see with HCl / HBr/ HI?

Answer 4

WHITE MISTY FUMES

Question 5

benzene + O2 →
(complete)

Answer 5

6CO2 + 3H2O

Question 6

benzene + O2 →
(incomplete)

Answer 6

3H2O + 6C
or
6CO + 3H2O
depending on Q - always 2 products

Question 7

benzene + bromine with catalyst →

Answer 7

catalyst FeBr3
bromobenzene + HBr

Question 8

what are the 4 stages of electrophilic substitution?

Answer 8

1. formation of electrophile
2. attack of electrophile
3. reformation of π system
4. reformation of catalyst

Question 9

benzene + conc nitric acid + catalyst →

Answer 9

catalyst conc H2SO4
nitrobenzene + H2O

Question 10

benzene + halogenoalkanes + catalyst →

Answer 10

catalyst AlCl3
alkyl benzene (or phenyl alkane) + halogenoalkane
in reflux

Question 11

benzene + acyl chloride + catalyst →

Answer 11

catalyst AlCl3
phenyl ketone + HCl

Question 12

what are methyl benzene’s properties?

Answer 12

alkyl group is e- pushing
so pushes e- density into pi system
so more easily attacked by electrophiles

Question 13

what’s another name for methyl benzene?

Answer 13

toluene

Question 14

is benzene or methyl benzene more reactive?

Answer 14

methyl benzene
has lower activation energy
e- pushing properties

Question 15

what is a phenol?

Answer 15

benzene with OH attached to one of the C

Question 16

phenol + bromine/bromine water →

Answer 16

2,4,6-tribromophenol + 3HBr
white ppt
no heating, no catalyst

Question 17

phenol + dil HNO3 →

Answer 17

2
DNF

Question 18

pH of phenol?

Answer 18

weak acid
reacts like alcohol
but more stable
due to resonance stability (feeing e- into delocalised pi system)

Question 19

what is the amine functional group?

Answer 19

N with lone pair

Question 20

What is the amide functional group?

Answer 20

-C=O
|
N

Question 21

How to identify amino acids?

Answer 21

Most have chiral C
Has amino group
and COOH group

Question 22

Butyl amine + water →

Answer 22

Butyl ammonium
+ OH-
OH- released makes alkaline solution!!!
as N in Butyl amine has lone pair

Question 23

Butyl amine + acid →

Answer 23

salt (+ water sometimes, not necessarily be in eq)

Question 24

1° amine + acyl chloride →

Answer 24

2° amine + HCl

Question 25

butyl amine + bromomethane →
if excess amine

Answer 25

single substitution
methyl butylamine + HBr / butylammonium bromide

Question 26

butyl amine + bromomethane →
if excess halogenoalkane

Answer 26

multiple substitutions

Question 27

butyl amine + copper(II) ions

Answer 27

form complex ions
has central metal ion with its covalently bonded ligand
Amines have a lone pair so can make dative covalent bonds

Question 28

What are the techniques to prepare and purify organic compounds?

Answer 28

1 reflux
2 purify by washing
3 solvent extraction
4 recrystallisation
5 drying
6 distillation
7 bp / mp determination

Question 29

Why is suction filtration good to purify organic solids?

Answer 29

Quicker and more dry than using just filter paper

Question 30

How to recrystallise to purify organic compounds?

Answer 30

1. Dissolve in minimal volume (so max mass of product recrystallised) of hot solvent (so solubility is higher)
2. Hot filtration using hot glass funnel and heated filter paper
3. cool solvent in ice
4. suction filtration 5 wash solid with ice cold water
5. Leave to suck dry
6. Transfer to warm oven

Question 31

Why is heated funnel and filter paper used in recrystallisation?

Answer 31

Prevent product from crystallising to maximise yield

Question 32

How to remove water?

Answer 32

Anhydrous sodium/magnesium sulphate (very fine powder)(so when water absorbed, will stay solids, won’t dissolve)

Question 33

Why is the thermometer bulb located at the sidearm in distillation?

Answer 33

It must read the temp of substance, gas collected

Question 34

What does steam distillation do?

Answer 34

Heating lots of water into steam
To change the environment so reaction mixture agitated by steam
lowers bp of organic substance that’s likely to decompose

Question 35

How does steam distillation lower bp of organic substance?

Answer 35

Reaction mixture agitated by steam
Changing the atmosphere and IMFs of environment ( from London to H bonds in water)
To its lowest decomposition point

Question 36

How to use melting temperature determination?

Answer 36

Use mp apparatus
To measure the temp of solid
If pure substance, all melt at one temp
If impure, will melt at a range of temps

Question 37

Is primary or tertiary amine more basic?

Answer 37

Tertiary
Because it is more e- pushing
Since it has most alkyl groups

Question 38

How to make primary amines from Halogenoalkane?

Answer 38

NH3 + R-X -> R-NH2 + HX or NH4X
(Excess NH3, sealed tube)

Question 39

How to make primary amines from nitriles?

Answer 39

Add reducing agent
LiAlH4 in dry ether // H2 + Ni catalyst

Question 40

Benzene + HNO3 ->

Answer 40

H2SO4 heat under reflux 50C
Makes nitrobenzene
+ 6[H] reflux in conc HCL + Sn
Make phenylamine + water

Question 41

How to make amides from acyl chloride?

Answer 41

Acyl chloride + primary/secondary ammonia -> HCl + amide

Question 42

What reaction is the formation of polyamides?

Answer 42

Condensation

Question 43

How to polyamide reaction?

Answer 43

H and Cl react like H and OH in esters

Question 44

Amino acid with carboxylate on the side refluxed in excess acid will make

Answer 44

Amino acid
But N has 3 H bonded to it, + charge
COOH on C2