Further synthesis and analysis

Question 1

Explain why chemists aim to design processes that do not require a solvent and that use non-hazardous starting materials

Answer 1

Avoiding solvents is a way of reducing the hazards associated with a process and the amount of waste created. solvents are often flammable and toxic. if the solvent has to be disposed of, this can create a lot of waste.

Question 2

Explain why chemists aim to design production methods with fewer steps that have a high percentage atom economy

Answer 2

Waste can be reduced by designing synthesis routes that have as few steps as possible.
They also try to design non-hazardous starting materials to limit the potential for accidents and environmental damage.

Question 3

What happens to nuclei when an external magnetic field is applied?

Answer 3

The nuclei align either with the field or opposed to it. The nuclei aligned with the external field are at a slightly lower energy field than the opposed nuclei.

Question 4

What does an NMR spectroscopy show?

Answer 4

• Nuclei in different environments absorb different amounts of energy at different frequencies.
• the differences in energy absorption between environments are shown on NMR spectroscopy

Question 5

What is the standard substance used in NMR and why?

Answer 5

TMS- tetramethylsilane

it is inert, non toxic and volatile

Question 6

What does a C-13 NMR show?

Answer 6

It shows how many different carbon environments are present

Question 7

What does a proton NMR show?

Answer 7

It shows how many environments are present and the relative area under each peak tells you the relative number of H atoms in each environment.

Question 8

What solvents are used in proton NMR?

Answer 8

deuterated solvents

hydrogen free solvents such as CCl4

Question 9

What are the two phases present in chromatography?

Answer 9

Mobile phase- the molecules can move and it is always a liquid or a gas
Stationary phase- the molecules can’t move. This must be a solid or a liquid on a solid support.

Question 10

What is the basic principle of chromatography?

Answer 10

• the mobile phase moves through or over the stationary phase
• the distance each substance moves up the plate depends on its solubility in the mobile phase
• components that are more soluble will travel further up the plate
• the differences in solubility and retention by the stationary phase separate out the different substances

Question 11

What is used to reveal colourless chemicals?

Answer 11

UV light
-many TLC plates have a special fluorescent plate that glows under UV light

Iodine
-iodine vapour is a locating agent that sticks to the chemicals on the plate and they’ll show up as brown/purple spots

Question 12

What property is used to identify substances using their position on a plate?

Answer 12

Rf values

Question 13

What is thin layer chromatography?

Answer 13

A plate is coated with a solid and a solvent moves up a plate

Question 14

What is column chromatography?

Answer 14

A column is packed with a solid and a solvent moves down the column

Question 15

What is gas chromatography?

Answer 15

A column is packed with a solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature

Question 16

What is the advantage of gas chromatography-mass spectrometry?

Answer 16

The components separated out by the chromatography can be positively identified which would be impossible with the chromatography alone.