C18 Organic Chem 3

Question 1

Formula for Benzene

Answer 1

C6H6

Question 2

Kekule Model for Benzene

Answer 2

Suggested that it was a planar ring of carbon atoms with alternating single and carbon bonds which constantly flipped

Question 3

How was Kekule Model for Benzene disproved

Answer 3

X-ray diffraction showed the carbon to carbon bonds were equal in length

Question 4

Delocalised Model

Answer 4

Each carbon atom has one p orbital which sticks above and below the plane of the ring.
These p orbitals overlap sideways, forming a ring of pi bonds that are delocalised around the carbon ring

Question 5

Evidence for Delocalised Model

Answer 5

Enthalpy changes of Hydrogenations show the differences in the predicted and actual as benzene is more stable than the Kekule Structure

Question 6

Why are electrophiles more susceptible to attack for alkenes that benzene

Answer 6

Alkenes have C=C bonds which have a high electron density which attracts electrophiles.
Benzene has a ring of delocalised electrons so the electron density / negative charge is more spread out so the attractions is reduced

Question 7

Combustion of benzene

Answer 7

Smoky flame due to lack of oxygen

Question 8

What reactions do arenes go under

Answer 8

Electrophilic substitution

Question 9

Benzene to halobenzene

Answer 9

Halogen
FeBr3
Electrophilic substitution

Question 10

Draw mechanism for
Benzene
Br2
FeBr3

Answer 10

search it up like fr fr fr

Question 11

Friedel Crafts Reactions

Answer 11

Alkylation
Acylation

Question 12

Friedel Crafts Alkylation Reactions

Answer 12

Haloalkane
AlCl3
Reflux

Question 13

Friedel Crafts Acylation Reactions

Answer 13

Acyl Chloride
AlCl3
Reflux

Question 14

Benzene to Nitrobenzene

Answer 14

Conc. HNO3 & Conc. H2SO4
Below <55 degrees Celsius

Question 15

Why is Phenol more reactive than Benzene

Answer 15

Lone pair of electrons on the oxygen atom is donated to the delocalised ring of electrons on benzene

which increases its electron density

so it’s more susceptible to attack by electrons.

Question 16

Haloalkane to Amine

Answer 16

Excess of ethanolic ammonia and heat in sealed tube under high pressure
Nucleophilic Substitution

Question 17

Nitrile to Amine 1

Answer 17

LiAlH4 in dry ether
Dilute Acid
Reduction

Question 18

Nitrile to Amine 2

Answer 18

Hydrogen
Ni cat.
High temp high pressure
Hydrogenation

Question 19

Nitrobenzene to Aromatic Amine

Answer 19

Sn
Conc. HCl
Reflux
NaOH
Reduction

Question 20

Order of strongest bases of:
phenylamine
ammonia
methylamine

and why

Answer 20

phenylamine
ammonia
methylamine

In phenylamine, the lone pair on N atom is donated to the delocalised ring of electrons so makes the lone pair less readily available

In methylamine, the alkyl groups are electron releasing so electron density on N atom increases making the lone pair more readily available to accept a proton

Question 21

Amine are good…

Answer 21

Bases

Question 22

Small Amine + water

Answer 22

+ and OH-

Question 23

Amine + acid

Answer 23

Ammonium salt

Question 24

Amine to N substituted Amide

Answer 24

Acyl Chloride
HCl
But Amine also reacts with HCl to form a salt
Solid white mixture of products form

Question 25

Acyl Chloride to Primary Amide

Answer 25

Conc. NH3

Question 26

Acyl Chloride to N substituted Amine

Answer 26

Primary Amine

Question 27

Polyamide

Answer 27

2 amino acids dicarboxylic acid and diamine diacyl chloride and di amine

Question 28

Protein to amino acids

Answer 28

6 mol/dm3 HCl heat under reflux NaOH

Question 29

Why are amino acids amphoteric

Answer 29

Contains basic amino group and acidic carboxyl group

Question 30

Amino acids normally exist as

Answer 30

zwitterions

Question 31

2-amino-acids

Answer 31

When their is 1 carbon attached to the c=o carboxyl and amino group

Question 32

Chromatography steps

Answer 32

Spot (of hydrolysate) on paper/tlc/thin layer chromatogram Marker spots of known aminoacids/measure Rf Run in (suitable) solvent/discussion of comparative solubilities in phases (Spray with) ninhydrin (and heat) Compare Rf values of marker spots with hydrolysate spots

Question 33

Grignard Reagent formula

Answer 33

R - Mg - X

Question 34

How to make a Grignard Reagent

Answer 34

Haloalkane Reagent : Mg in dry ether Conditions: reflux

Question 35

Grignard Reagents reactions

Answer 35

CO2 Carbonyls

Question 36

R-Mg-X to Carboxylic acid

Answer 36

CO2 in dry ether Dilute HCl

Question 37

R-Mg-X to Alcohol

Answer 37

Carbonyl in dry ether Dilute HCl

Question 38

When is Steam Distillation used

Answer 38

- organic liquids have very high BPs - some organic liquids decompose when heated

Question 39

What is the main concept of steam distillation

Answer 39

Presence of steam lowers the boiling point of the immiscible product so it can evaporate at a lower BP before it decomposes

Question 40

When do you use a separating funnel

Answer 40

If a product is insoluble in water, then you can use separation to remove any impurities that do dissolve in water

Question 41

Solvent extraction is used when

Answer 41

Compounds in a mixture are both soluble in water

Question 42

Process of solvent extraction

Answer 42

Add impure compound into separating funnel Add water Shake well Add an organic solvent so products will dissolve in it Add a salt so the organic product moves into the organic layer Separates into product and aqueous layer with the impurities Discard layers

Question 43

Drying agents

Answer 43

Add an anhydrous salt like CaCl2 or MgSO4 and filter it

Question 44

Hot filtration for when u want the solid

Answer 44

Place filter paper on Buchner funnel Wet paper with solvent Turn vacuum on and pour mixture into the funnel. Flask is under reduced pressure so liquid is sucked into the flask Rinse solid with solvent Wash off any of the original liquid

Question 45

Recrystillisation

Answer 45

Very hot solvent is added to the impure solid until it dissolves to give a saturated solution of the impure product Filter Let solution cool slowly Crystallises Remove crystals by filtration under reduced pressure

Question 46

Choice of solvent

Answer 46

Very soluble when hot Insoluble when cool

Question 47

Measuring Melting Points of an Organic Solid

Answer 47

Pack a small sample of the solid into a glass capillary tube Place into a heating element Increase temp so it melts Measure the melting range Compare with data book values

Question 48

Do impurities increase or decrease BP

Answer 48

INCREASE

Question 49

Do impurities increase or decrease MP

Answer 49

DECREASE

Question 50

Recrystillation

Answer 50

Insoluble impurities are removed by the hot filtration Soluble impurities are removed by the cold filtration