Esters, Optical Isomerism and Aromatic Hydrocarbons

Question 1

What do we use as a reference for NMR Spectroscopy? What is the structure of this?

Answer 1

TMS - a Si atom with 4 methyl groups attached.

Question 2

What properties of the reference for NMR Spec. make it appropriate? (5)

Answer 2

It is inert, non-toxic, volatile (so you can easily remove it), same environment and it is found to the far right of the spectrum so it is easy to distinguish.

Question 3

What solvents do we use for NMR Spectroscopy? When would we use each one?

Answer 3

CDCl₃, CCl₄ or D₂O (each of these have even mass numbers so they won’t show up). Esters are not water soluble, so CCl₄.

Question 4

How can we measure if a compound is an optical isomer?

Answer 4

We can use a polarimeter.

Question 5

What is a racemic mixture (also known as a racemate)?

Answer 5

A 50/50 mixture of the R and S enantiomers.

Question 6

Can a molecule with a C=O from the chiral centre be an enantiomer?

Answer 6

Yes.

Question 7

Why do we do melting point synthesis?

Answer 7

It is quick and simple and does not use any specialist equipment (like mass spectrometers would).

Question 8

How does the melting point of an impure product compare with that of a pure product?

Answer 8

The melting point of an impure product happens at a lower temperature, and also occurs over a range of temperatures.

Question 9

What is a carbonyl group?

Answer 9

C=O

Question 10

How can we oxidise a ketone?

Answer 10

Using a stronger oxidising agent; potassium manganate solution (we need a stronger oxidising agent because C-C bonds need to be broken).

Question 11

How do we represent a reducing agent in chemical equations?

Answer 11

[H]

Question 12

Give the molecular formula of our reducing agent that we commonly use.

Answer 12

NaBH₄

Question 13

What is the general name given to molecules with a C≡N and an O-H group?

Answer 13

Hydroxynitride.

Question 14

What is the catalyst for forming an ester from a carboxylic acid?

Answer 14

A concentrated acid, like sulphuric acid or phosphoric acid.

Question 15

What is acylation?

Answer 15

Where an acyl group (R-C=O-R’) is attached to a molecule.

Question 16

Give the general mechanism for nucleophilic addition with a ketone.

Answer 16

Question 17

Give the name and the mechanism for the reaction of ammonia with ethanoic anhydride.

Answer 17

Nucleophilic Addition Elimination

Question 18

Why can potentially bad nucleophiles, such as water, be used with certian molecules like ethanoic anhydride or an acyl chloride?

Answer 18

Because the carbon is surrounded by more electronegative groups (such as an oxygen and a carbon), which makes them have a larger δ+ charge, so they’re more susceptible to attack.

Question 19

How do we synthesise an acyl chloride?

Answer 19

We react a carboxylic acid with phosphorous (V) chloride, PCl₃, or use P₄O₁₀. The image attached shows PCl₃.

Question 20

How is aspirin formed?

Answer 20

Via an esterification reaction from sacylic acid (an acid anhydride) using ethanoic anhydride (and then it is purified by dissolving it in ehtanol, crystallising it in cold water and filtering it under reduced pressure).

Question 21

Why do we use an acid anhydride (salicylic acid) rather than an acyl chloride? (4)

Answer 21

• Acid anhydrides are cheaper than acyl chlorides;
• Acid anhydrides are less corrosive (HCl is a by-product of using acyl chlorides) so equipment is cheaper as it need not be glass-lined;
• Acid anhydrides do not react as readily with water;
• The by-products of acid anhydrides are safer to handle.

Question 22

What is an amine and how are they categorised?

Answer 22

A molecule which has had its hydrogens replaced by hydrocarbon groups. They can be categorised as primary (RNH₂), secondary (RNHR’) and tertiary (RR’NR’’) amines.

Question 23

How can we make an aromatic amine?

Answer 23

Using hydrogen and a tin cayalyst after the nitration of benzene. This forms C₆H₆NH₂.

Question 24

Give an application of nitration.

Answer 24

To make TNT, which is where methylbenzene is nitrated.

Question 25

Give a use of benzene compounds in the clothing industry.

Answer 25

Icedyes.

Question 26

How do we produce a nitronium ion for use in nitration?

Answer 26

Two steps (both the sulphuric acid and the nitric acid need to be concentrated):

H₂SO₄ + HNO₃ → H₂NO₃⁺ + HSO₄^-

H₂NO₃⁺ + H₂SO₄ → NO₂⁺ + H₃O⁺ + HSO₄^-

Question 27

Give the “proper” name of the mechanism for nitration and outline it.

Answer 27

Question 28

Give the name of the process and the mechanism for the reaction of benzene with H₃C-+C=O.

Answer 28

Friedel-Crafts Acylation

Question 29

What is the transesterification process used for and what is the catalyst?

Answer 29

To produce biodiesel from oils.

Question 30

Give the reaction for the transesterification of a triglyceride with methanol (name of product, displayed formula and balanced).

Answer 30

Question 31

Give the name and the use of the by-product of transesterification.

Answer 31

Glycerin. This heavier product can settle off and be removed and can be sold off to be used in the pharmaceutical industry.

Question 32

Under what conditions does addition polymerisation occur?

Answer 32

High pressure and a catalyst (no name needed).