Further Synthesis and Analysis

Question 1

What do chemists do to make synthesis routes safe and efficient?

Answer 1

• They use non-hazardous starting materials to limit the potential for accidents and environmental damage
• They try to make the process less wasteful by doing reactions with high atom economies and percentage yields.
• They also try to reduce waste by designing synthesis routes that have the fewest steps as possible

Question 1

What is the importance of synthesis routes?

Answer 1

It allows chemists to make desired compounds from another. It is useful for things like designing medicines and making imitations of natural substances when the real thing is hard to extract.

Question 2

What are the dangers/wastes of solvents in synthesis routes?

Answer 2

Avoiding using solvents wherever possible is one way of reducing both the hazards associated with a process and the amount of waste created by a synthesis route. Solvents are often flammable and toxic so can pose safety risks. If the solvent has to be disposed of after the reaction is complete, that can also create a lot of waste.

Question 3

What are the two types of NMR?

Answer 3

Carbon 13 NMR gives you information about how the carbon atoms in a molecule are arranged, and proton NMR tells you how the hydrogen atoms in a molecule are arranged.

Question 4

What causes a nuclear spin and why is it important in NMR?

Answer 4

Any atomic nucleus with an off number of nucleons in its nucleus has a nuclear spin. This causes it to have a weak magnetic field- a bit like a bar magnet. NMR spectroscopy looks at how this tiny magnetic field reacts when you put in a much larger external magnetic field.

Question 5

What happens to nuclei when exposed to a strong external magnetic field?

Answer 5

They will all align either with the field or against it.
The nuclei aligned with the magnetic field are at a slightly lower energy level than the opposed nuclei

Question 6

What do radio waves do to nuclei?

Answer 6

Radio waves of the right frequency can give the nuclei that are aligned with the external magnetic field enough energy to flip up to a higher energy level. The nuclei opposed to the ecternal field can emit radio waves and flip down to the lower energy level.

Question 7

Why will nuclei in different environments absorb different amounts of energy at different frequencies?

Answer 7

Nuclei are partially shielded from the effects of external magnetic fields by their surrounding electrons and the groups of atoms around a nucleus will affect its electron shielding.

Question 8

What is the reference molecule in NMR?

Answer 8

Tetramethylsilane (TMS)
It has 12 hydrogen atoms in identical environments, so it produces a single absorption peak, well away from most other absorption peaks.

Question 9

What do the peaks in carbon NMR mean?

Answer 9

Each peak on the spectrum corresponds to a different carbon environment

Question 10

What do the peaks in proton NMR mean?

Answer 10

Each peak on the spectrum corresponds to a different hydrogen environment

Question 11

What do the numbers above the peaks in proton NMR mean?

Answer 11

They tell you the ratio of the areas under the peaks. This relative area under each peak also tells you the relative number of H atoms in each environment.

Question 12

How do you work out splitting patterns in proton NMR?

Answer 12

Count the number of H atoms on neighboring carbons + 1
singlet
doublet
triplet
quartet
quintet

Question 13

Why must samples be dissolved in hydrogen free solvents in NMR?

Answer 13

• the H atoms would show up on the spectrum as they have a spin state
• instead should use deuterated solvents
• CCl4 can also be used as a solvent