Chemistry 2301
Thursday, December 5
At-Home Exercise:
IR Spectroscopy and MS Fragmentation Patterns
Cladosporium resinae, sometimes called “fuel fungus”, colonizes aircraft fuel lines in
wet climates. To use aircraft fuel as food, the fungus must first oxidize the fuel’s
component hydrocarbons. To better understand this process, C. resinae was grown on
n-pentane and oxygen, and initial metabolites were collected and analyzed by IR and
MS. In this problem, you will try to determine the structure of one metabolite from IR and
mass spectra.
a. The IR spectrum of one pentane metabolite is shown below.
Transmittance (%)
100
50
0
4000
3000
2000
1500
1000
500
Wavenumbers (cm-1)
Hydrocarbon oxidation could presumably generate any of the functional groups
shown below. Based on the IR spectrum, which would you predict to find in this
metabolite? Circle all answers that apply.
H
C
(sp)
C(sp 2)
H
H
C(sp 3)
H
O
C
C
O
C
b. Let’s assume that the metabolite still has the linear, five-carbon skeleton of npentane. Given your answers to part (a), what are some possible structures for the
molecule?
c. The mass spectrum of the metabolite is shown below.
Relative Intensity
100
45
80
60
40
88
20
73
0
10
20
30
40
50
60
70
80
90
100
m/z
Let’s assume that the parent mass for [M+] has m/z = 88. Is this consistent with any
of the structures you drew in part (b)? (Do any of them have mass 88 amu?)
d. Which of your proposed structures is also consistent with fragment masses of m/z =
45 and 73 amu? How would your molecule have to fragment to generate these
masses?
e. In the mass spectrum, the peak at m/z = 45 is much taller than the peak at m/z = 73.
Why do you suppose the m/z = 45 fragment is produced so much more than the m/z
= 73 fragment?