Module 4.2 - Alcohols, Haloalkanes and Analysis

Question 1

What is the general formula of alcohols?

Answer 1

C(n)H(2n+1)OH

Question 2

Describe primary alcohols

Answer 2

Alcohol attached at the end of the chain with one alkyl chain attached.

Question 3

Describe secondary alcohols

Answer 3

Alcohol attached to 2 alkyl chains and a hydrogen atom.

Question 4

Describe tertiary alcohols

Answer 4

Alcohols attached to 3 alkyl chains

Question 5

Describe the trend in boiling points of alcohols.

Answer 5

> Increases as chain length increases.
More surface area contacts
Stronger induced dipole-dipole IMFs
More energy needed to overcome IMFs.

Question 6

Compare the boiling points of alcohols with their corresponding alkanes.

Answer 6

Alcohols have a higher boiling points than their corresponding alkanes due to hydrogen bonding in which are stronger than induced dipole-dipole interactions (London forces)

Question 7

What does the volatility of alcohols mean?

Answer 7

How easily alcohols evaporate at RTP.

Question 8

Describe the volatility of alcohols

Answer 8

Volatility increases as boiling points decrease. Therefore short chain alcohols are the most volatile.

Question 9

Compare the volatility of alcohols with their corresponding alkanes.

Answer 9

Alcohols have hydrogen bonding which means that they are less volatile than their corresponding alkanes as their boiling points are higher on average.

Question 10

Describe the solubility of alcohols

Answer 10

Alcohols are soluble in water as water molecules are polar and so is the functional group, therefore hydrogen bonds can be formed with the molecules.

Question 11

Define nucleophile

Answer 11

An electron pair donor.

Question 12

What happens as CFCs are exposed to UV light?

Answer 12

The C-Cl bonds undergo homolytic fission creating chlorine radicals.

Question 13

What is the problem with chlorine radicals being formed by CFCs in the environment?

Answer 13

They catalyse the decomposition of ozone. The chlorine radicals attack the ozone molecules and turns them into diatomic oxygen.

Question 14

What is the result of chlorine radicals converting ozone?

Answer 14

The ozone layer is shrinking and in some places there is no ozone in the upper stratosphere or low troposphere.

Question 15

What causes covalent bonds to vibrate more and absorb energy?

Answer 15

Infrared radiation

Question 16

Every bond vibrates at its own unique frequency. What does the amount of radiation depend on?

Answer 16

> Bond strength
Bond length
Mass of each atom involved in the bonds.

Question 17

How is the absorption of IR linked to global warming? What has this led?

Answer 17

Greenhouse gases often contain C=O, O-H and C-H which are very good at absorbing IR. This has led to the use of technologies and resources that do not emit greenhouse gases.

Question 18

How can you identify alcohols from an infrared spectrum?

Answer 18

> Alcohols show a key broad absorption peak between 3200-3600 cm^-1
Due to presence of O-H bond.

Question 19

How can you identify aldehydes and ketones from an infrared spectrum?

Answer 19

> Only peak at 1680-1750 cm^-1 in both aldehydes and ketones.
Represents the C=O bond

Question 20

How can you identify carboxylic acids from an infrared spectrum?

Answer 20

> Peak at 1680-1750 cm^-1 (also in aldehydes and ketones) - represents C=O bond.
Very broad peak at 2500-3300 cm^-1 - represents O-H bonds.

Question 21

What are the use of mass spectrometry?

Answer 21

> To identify the molecular ion peak.

> And hence to determine molecular mass.

Question 22

Briefly describe the process of mass spectrometry

Answer 22

1. Ionisation - atoms ionised to form positive ions called Molecular ions (M+)
2. Acceleration - ions are accelerated. Negatively charged plates attract M+.
3. Deflection - ions are deflected using a magnetic field. Most deflected have a higher m/z.
4. Detection - the beam of electrons are detected electronically.

Question 23

How and why does the molecular ion break up?

Answer 23

> As the molecular ion is unstable.
Will break into smaller pieces.
Due to excess energy from Ionisation.
Can be broken further.

Question 24

What does a molecular ion break up into?

Answer 24

A positive fragment ion and a neutral species - free radical.

Question 25

What are two uses of infrared spectroscopy?

Answer 25

> To monitor gases causing air pollution.

> In modern breathalysers to measure ethanol in the breath.