Mass Spec and IR
Mass spec practice: 2,2-diethylpentane; benzaldehyde
benzaldehyde
What is m/z for the parent peak of benzaldehyde? _______ 106
What is m/z for the major positively charged fragment? ________ 105
Draw the expected structure of the major positively charged
fragment
+ go through 1-3 and explain 7 together
(plus resonance structure)
1. Define:
a. Molecular ion – ion formed by taking away one electron from the molecule
b. Parent peak – the peak on the mass spectrum corresponding to the molecular ion
c. Base peak – most abundant ion (probably not the same as the parent peak)
2. What is on the x-axis of a mass spectrum?
a. m/z (mass/charge; charge is always +1)
3. Which of the following peaks does not appear in the mass spectrum of hexane? Draw the ions
corresponding to the other three peaks.
a. m/z = 57
b. m/z = 86
c. m/z = 36
d. m/z = 43
4. Which of the following regions in the electromagnetic spectrum corresponds to the radiation
with the highest energy?
a. Ultraviolet
b. Infrared
c. Visible
d. Radio waves
5. Which of the following is associated with absorption in the infrared region?
a. Bond vibration (IR)
b. Rotation of molecules (microwave)
c. Electron excitation (visible)
d. Nuclear spin flip (NMR)
6. What is the x-axis of an IR spectrum and what are its units? Wavenumber, in cm-1
7. Draw the bond which gives the following IR absorptions:
a. 1100 cm-1
(C-O)
-1
b. 1700 cm
(C=O)
-1
c. 3500 cm
(O-H)
8.
Which of the following are the expected products of the cleavage of 2pentanone (shown here) in mass spec?
1
9. Which of the following has a strong peak at 1720 cm-1 on its IR spectrum?
2
10.
a. Which of the above gives an IR spectrum with a strong broad peak at 2500-3100 cm-1
and a strong peak at 1712 cm-1? (3)
b. Which of the above gives an IR spectrum with a strong peak at 1715cm-1 but no peaks
at 1050-1150cm-1 and no broad peak at 2500-3100cm-1? (2)
11.
t-butane
a. What is m/z for the parent peak?
b. What is m/z for the major positively charged fragment?
c. Draw the expected structure of the major positively charged fragment
12.
13.
acetone
a. What is m/z for the parent peak of acetone? ______ 58
b. What is m/z for the major positively charged fragment? _____ 43
c. Draw the expected structure of the major positively charged fragment:
acetophenone
a. What is m/z for the parent peak of acetophenone? _____
b. Give the structure and m/z value for the lower molecular weight positively charged
fragment:
c. Give the structure and m/z value for the higher molecular weight positively charged
fragment:
14. Which of the following compounds is most likely to correspond to the mass spectrum below?