Yr 2 Organic chem

Question 1

What is the molecular formula for benzene?

Answer 1

C6H6

Question 2

What is the experimental evidence for the delocalised structure of benzene?

Answer 2

Bond lengths - All the same, when C=C bonds are shorter than C-C bonds. all somewhere between the bond length of a single and double carbon-carbon bond
Enthalpy change of hydrogenation - for Cyclohexene is -120kJ per mole, in Cyclohexadiene it is -240kJ per mole, meaning for the Kekule structure the expected enthalpy change would be -360kJ per mole, but it is actually much less exothermic (-208kJ per mole) - actual structure of benzene is more stable than the Kekulé structure
Resistance to reaction - if contained C=C bonds would decolourise bromine water, but it does not - more resistant to reaction than alkenes, does not react by electrophilic addition

Question 3

What is a substituent group?

Answer 3

An atom or group of atoms that takes the place of another.

Question 4

What are benzene and substituted aromatic hydrocarbons called?

Answer 4

Arenes

Question 5

What conditions are required for the nitration of benzene and what is the reaction mechanism?

Answer 5

50C, conc sulfuric acid catalyst and conc nitric acid

Electrophilic substitution

Question 6

What is used as a catalyst for the halogenation of benzene?

Answer 6

A halogen carrier, e.g. AlBr3

Question 7

When an acyl chloride reacts with benzene by electrophilic substitution what is formed?

Answer 7

An aromatic ketone

Question 8

Explain how phenols are weak acids

Answer 8

They partially dissociate in water to form phenoxide ions and protons. They are more acidic than alcohols but less acidic than carboxylic acids

Question 9

How can you distinguish between a carboxylic acid and a phenol?

Answer 9

Add sodium carbonate - carboxylic acids react to form carbon dioxide gas, phenols do not react and no effervescence occurs

Question 10

What type of reaction is the reaction of phenol with sodium hydroxide?

Answer 10

Neutralisation

Question 11

What is used to reduce carbonyls?

Answer 11

NaBH4 (H- hydride ion)

Question 12

What are used to produce HCN?

Answer 12

NaCN and H2SO4

Question 13

What is used to detect the presence of the carbonyl group and what is observed?

Answer 13

2,4-DNPH, orange precipitate forms

Question 14

How can the 2,4-DNPH derivative be analysed to identify the carbonyl compound?

Answer 14

Impure orange solid is filtered then recrystallised to produce a pure sample of the 2,4-DNPH derivative. The melting point of the purified 2,4-DNPH derivative is determined. The melting point is matched to a database of melting points for 2,4-DNPH derivatives of carbonyl compounds

Question 15

What is used to determine the presence of an aldehyde? What is observed?

Answer 15

Ammoniacal silver nitrate (Tollens’ reagent)

Silver mirror on inside of boiling tube

Question 16

Why do ketones not form a silver mirror when reacted with tollens’ reagent?

Answer 16

They cannot be reduced any further (by Ag+ ions in this case), whereas aldehydes can (to carboxylic acids)

Question 17

What are the reagents and conditions for esterification?

Answer 17

Concentrated sulfuric acid, warm

Question 18

Acid hydrolysis of esters

Answer 18

Reflux with dilute sulfuric acid - reverse reaction to esterification

Question 19

Alkaline hydrolysis of esters

Answer 19

Reflux with aqueous alkali - forms carboxylate ion and alcohol - irreversible

Question 20

How are acyl chlorides prepared?

Answer 20

By reacting carboxylic acids with thionyl chloride (SOCl2)

Question 21

What can acyl chlorides be used to produce?

Answer 21

Esters (aliphatic and aromatic), carboxylic acids, primary and secondary amides

Question 22

How do you produce a carboxylic acid from and amide?

Answer 22

React it with water (HCl is second product)

Question 23

How do you form a primary amide from an acyl chloride?

Answer 23

React with ammonia

CH3COCl + 2NH3 –> CH3CONH2 + NH4+Cl-

Question 24

How do you form a secondary amide from an acyl chloride?

Answer 24

React with an amine

CH3COCl + 2CH3NH2 –> CH3CONHCH3 + CH3NH3+Cl-

Question 25

Why would an acid anhydride be used over an acyl chloride?

Answer 25

Less reactive so are useful for laboratory reactions where acyl chlorides may be too reactive

Question 26

Give an example of a tertiary amine

Answer 26

Trimethyl amine

Question 27

How do amines act as bases?

Answer 27

The lone pair on the N atom can accept protons (H+ ions) in aqueous solution to form dative covalent bonds (___ammonium ions)

Question 28

Show the reaction of ethylamine with hydrochloric acid. What type of reaction is this?

Answer 28

CH3CH2NH2 + HCl --> CH3CH2NH3+Cl- | Neutralisation reaction

Question 29

How are primary amines prepared?

Answer 29

CH3CH2Cl + NH3 --> CH3CH2NH3+Cl- CH3CH2NH3+Cl- + NaOH --> CH3CH2NH2 + NaCl + H2O Ethanol is used as a solvent to prevent substitution of haloalkane by water to produce alcohols - excess ammonia in ethanol

Question 30

How are aromatic amines produced?

Answer 30

C6H5NO2 + 6[H] --> C6H5NH2 + 2H2O 1 Sn/conc HCl (reducing agent) 2 excess NaOH(aq)

Question 31

What do you need to remember when amino acids are esterified?

Answer 31

The NH2 amine group is protonated, so a proton must be involved in the reactants of the equation

Question 32

Where are optical isomers found in organic chemistry?

Answer 32

In molecules that contain a carbon atom that is a chiral centre you fucking moron bitch. A chiral carbon atom is bonded to four different atoms or groups of atoms

Question 33

What are optical isomers?

Answer 33

Non-superimposable mirror images with a chiral centre

Question 34

What does acid hydrolysis of polyamides produce?

Answer 34

Dicarboxylic acid and diammonium salt

Question 35

What does alkaline hydrolysis of polyamides produce?

Answer 35

Dicarboxylate salt and diamine

Question 36

How do you calculate number of optical isomers?

Answer 36

2 to the power of n (n being the number of chiral carbon atoms)

Question 37

What is the reaction mechanism for the conversion of haloalkanes into nitriles and what is required?

Answer 37

Nucleophilic substitution | Ethanol is required as a solvent

Question 38

How are nitriles reduced (to amines) and what is the catalyst?

Answer 38

By reacting them with hydrogen in the presence of a nickel catalyst

Question 39

How are nitriles hydrolysed to carboxylic acids?

Answer 39

Heating with dilute aqueous acid (HCl)

Question 40

Minimum volume of hot solvent added (recrystallisation)

Answer 40

Yes.