Chapter 12 - Structure Determination: Mass Spectrometry and Infrared Spectroscopy
Mass Spectrometry Assignment
1. Give the formula for each of the following compounds with the mass spectral data below: SHOW
WORK/EXPLAIN
a) A hydroca
on with M+ at m/z = 86.
) A compound that is an unsaturated ketone that contains three double bonds and one ring and with M+ at
m/z = 150.
c) A compound with a degree of unsaturation of 8, that contains C, H, and O and with M+ at m/z = 360.
C21H28O5.
d) M+ at m/z = 101 with a minor M+1 peak. Select from these: C5H6Cl; C5H12N2; C6H15N; C9H12O
e) M+ m/z = 136 and M+ at m/z = 138 of approximately equal intensity. Select from these: C6H13OCl;
C4H9Br; C10H16; C9H12O
2. The mass spectral analysis of a compound shows M+ at m/z = 382 and M+ at m/z = 384 in an approximate
atio of 3:1 in intensity. Use the data below to answer the following question(s).
a) Which halogen does the mass spectral data indicates that the compound contains?
) This compound is known to contain nitrogen. What is the minimum number of nitrogens in this
compound?
c) The compound also contains oxygen. What is the molecular formula of the compound?
3. Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s).
a) What peak represents M+?
) What peak represents the base peak?
c) Propose the mechanism that produce the fragment ions at m/z = 57, 43, and 29.
Mass Spectrometry Assignment
4. Consider the following mass spectrum
a) Which of the following compounds might have been used to produce this spectrum?
C6H14; C6H12; C6H10; C5H12O. Explain your answer.
) Show the mechanism for all the fragmentations of this compound.
5. Could you distinguish 2,2-dimethylbutane from 2-methylpentane using mass spectrometry? Explain
showing mechanisms for fragmentation to support your answers.
6. Both methylcycloheptane and ethylcyclohexane have the same molecular mass. Explain how it is possible
to distinguish between the two compounds by studying and comparing both their mass spectra. Show
mechanisms for fragmentation to support your answers.
7. Two mass spectra are shown in the figure below. One spectrum is that of 2-methyl-2-pentene, the other is
of 2-hexene. Which is which? Explain. Show the mechanism for all the fragmentations for each compound.
Mass Spectrometry Assignment
8. The following question(s) refer to the mass spectrum shown below.
a) This compound contains C, H, and one other atom. Identify the other atom from the mass spectrum
and explain your reasoning.
) Calculate a possible molecular formula for this compound.
c) Propose a structure for this compound.
9. For each compound below, what are the masses of the charged fragments produced by the indicated
cleavage pathways? Show mechanisms.
a) Alpha cleavage of
) Alpha cleavage and dehydration of
10. For each compound below, what are the masses of the charged fragments produced by the indicated
cleavage pathways? Show mechanism
a) Alpha cleavage of 2-pentanone
) Dehydration of cyclohexanol
c) McLafferty rea
angement of 4-methyl-2-pentanone
d) Alpha cleavage of triethylamine