Mass Spectrometry

Question 1

How do you know if you’ll be able to distinguish the difference between compounds depending on resolution?

Answer 1

Find the difference in ppm and see if it is higher than resolution

Question 2

How do you use relative abundance to find intensities of peaks

Answer 2

If F or I then ignore

If Cl or Br then consider how many there are and use binomial expansions to find it

Question 3

Explain alpha cleavage

Answer 3

When lp becomes a radical then cleavage is possible at the alpha site

Question 4

Explain the mclaferty rearrangment

Answer 4

hydrogens gamma to carbonyl can be exchanged. This causes a subsequent c cleavage

Question 5

Explain how H rearrangment takes place in the cleavage of a cyclic molecule.

Answer 5

Alpha cleavage. Resulting radical can exchange a proton neaby before radical performs a carbon cleavage

Question 6

What’s something special about an odd m/z

Answer 6

Compound likely contains nitrogen

Question 7

For a reverse diels alder reaction, which molecules will be charged and be radicals if EI is used?

Answer 7

The diene is favored due to higher conjugation and stability

Question 8

For the loss of

1, 15, 29, 31, 43 and 45 what

What are possible leaving groups?

Answer 8

1 = H

15 = CH₃

29 = .CH₂CH₂CH₃ or .CHO

31 = .OMe

43 = .CH₂CH₂CH₂CH₃

45 = Ac. or CO₂H

Question 9

For the loss of

18, 28, 44, 90

What are possible leaving groups?

Answer 9

18 = H₂O

28 = CO

44 = CO₂

90 = HO-Si-(CH₃)₃

Question 10

What is the natural abundance and molecular mass of all isotopes of Br?

Answer 10

Br, 79 & 81

50%, 50% abundance respectively

Question 11

What is the natural abundance and molecular mass of all isotopes of F?

Answer 11

F, 19

100%

Question 12

What is the natural abundance and molecular mass of all isotopes of I?

Answer 12

I, 127

100%

Question 13

What is the natural abundance and molecular mass of all isotopes of Cl?

Answer 13

Cl, 35, 37

75% and 25% respectively