PL.9

Question 1

To what accuracy can modern high-resolution mass spectrometers measure the relative molecular masses of ions?

Answer 1

To four decimal places.

Question 2

What about a molecule can be directly worked out using high-res mass spectrometers?

Answer 2

Its Mr to four decimal places, therefore its molecular formula.

Question 3

Can the structural formula be determined with the Mr determined by high-res mass spectrometers?

Answer 3

No, other methods have to be used.

Question 4

For each fragmentation, do both fragment products have a positive charge?

Answer 4

No, only one fragment keeps the positive charge, meaning that although the positive charge is normally given to the most stable ion, there are always the possibility of two different ions.

Question 5

What are the two most common types of NMR spectrometry?

Answer 5

C13 NMR and H1 NMR.

Question 6

What does an atom have to have to be able to be used in NMR?

Answer 6

It must have an odd number of protons or neutrons in its nucleus, they can able to behave like little magnets when placed in a strong magnetic field.

Question 7

What is zero set to in the NMR spectrums?

Answer 7

TMS peak, given by the absorption of C13 or H1 in tetramethylsilane, Si(CH3)4. This molecule gives one peak as all C13 or H1 are in the same environment.

Question 8

Why is TMS chosen as a standard reference in NMR?

Answer 8

Because it gives a single sharp peak that is away from most peaks of interest to chemists.

Question 9

What is the extent to which a signal differs from TMS (0) known as?

Answer 9

The chemical shift.

Question 10

What are two things that C13 NMR can be useful for?

Answer 10

1. Used to work out the number of carbon environments in the molecule which corresponds to the number of peaks.
2. Used to roughly identify the groups the carbon atoms are attached to.

Question 11

Why does the splitting pattern in H1 NMR depend on?

Answer 11

The number of hydrogen atoms on the adjacent carbon atom by the n+1 rule.

Question 12

A singlet peak indicates how many adjacent hydrogen atoms?

Answer 12

No adjacent hydrogen atoms.

Question 13

A doublet peak indicates how many adjacent hydrogen atoms?

Answer 13

1

Question 14

A triplet peak indicates how many adjacent hydrogen atoms?

Answer 14

2

Question 15

A quartet peak indicates how many adjacent hydrogen atoms?

Answer 15

3

Question 16

What are four things that H1 NMR can be useful for?

Answer 16

1. Used to identify the number of hydrogen environments in the molecule.
2. Used to identify the number of hydrogen atoms in each environment. (If given integrated data)
3. The nature of the environments. Such what groups are connected to the carbon carrying the hydrogens.
4. How many hydrogen atoms are in adjacent environments using the n+1 rule and splitting patterns.