Mass Spectra Interpretation: ALCOHOLS
Quiz Instructions:
Electron impact Mass Spectrometry produced the spectra below. Many Peaks are labelled to aid interpretation: M/Z (relative abundance). Look at the Hints for help. You will need a Periodic Table, a Table of Common Isotopes, a calculator, and scratch paper to work the quiz.
No. of Questions = 9
1. Identify the molecular ion in this spectrum.
WRONG --> this is the molecular ion less 1 hydrogen
CORRECT --> the isotope peak for 46 is 47, and the relative ratio of 47 to 46 is 2.4, which is reasonable
WRONG --> this is the isotope peak for the molecular ion
2. For this same spectrum, choose the compound that the spectrum represents.
WRONG --> in this compound (HCOOH), the 31 peak is not possible
WRONG --> MW is too high (60)
CORRECT --> MW is 46, 31 formed by loss of 15 (CH3) from 46
WRONG --> MW is too low (32)
WRONG --> MW is too high (60)
3. Find the alkyl ion series in the spectrum below. (Check the Hint)
CORRECT --> CH3, CH2CH3, CH2CH2CH3, CH2CH2CH2CH3
WRONG --> this is formed by alkyl LOSS
WRONG --> there are patterns
4. Find the alkyl LOSS ion series in the same spectra shown below. (Check the Hint)
WRONG --> this is the alkyl series
CORRECT --> this is the loss series observed in the spectrum: 74-43=31, 74-29=45
WRONG --> there is a series
5. For the same spectrum shown in the previous two questions, choose the compound that the spectrum represents.
WRONG --> in this compound, the tert-carbon would stabilize a fragment at 59, reducing other intensities
CORRECT --> MW is 74, 56 is formed by loss of 18 (H2O) from 74
WRONG --> in this compound, substitution would increase one or two fragments, and you would not observe a lot of intense fragments.
WRONG --> MW is too high (88)
WRONG --> in this compound, substitution would increase one or two fragments, and you would not observe a lot of intense fragments.
6. Identify the molecular ion in this spectrum.
WRONG --> this is the fragment from the molecular ion less water (88-18=70)
WRONG --> this is an alkyl ion series ion
WRONG --> this is the molecular ion less one hydrogen (88-1=87)
CORRECT --> MW is 88, 70 formed by the loss of 18 (H2O) from 88
7. For the same spectrum, choose the compound that the spectrum represents.
WRONG --> MW is too high (102)
CORRECT --> MW is 88, 42 is formed by loss of 18 (H2O) and 28 (CH2CH2) from 88
WRONG --> in this compound, the tert-carbon would stabilize a fragment at 59, reducing other intensities
WRONG --> in this compound, the substitution would increase the intensity of 45
WRONG --> MW is too low (74)
8. Choose the compound that this spectrum represents.
WRONG --> MW is too high (88)
CORRECT --> MW is 74, 59 formed by loss of 15 (CH3) from 74
WRONG --> branch at 2nd position would increase the intensity of 45 (not 59)
WRONG --> no branching would increase the intensity of other peaks (not just 45)
WRONG --> alpha cleavage would increase 31 relative to other fragments.
9. Choose the compound that this spectrum represents.
WRONG --> MW is too high (88)
WRONG --> in this compound, the high intensity peak would be 59 (not 45)
WRONG --> in this compound, no branching would increase the intensity of other peaks (not just 45)
WRONG --> in this compound, tert-carbon would stabilize m/z 59, reducing other intensities
CORRECT --> MW is 74, 45 formed by loss of CH2CH3 (29) from 74