Question

The Tabular data of unknowns 1 to 3 also show small peaks of masses above that corresponding to the molecular weight. These are due to the presence of less-abundant isotopes, the carbon-12 found in nature must be accompanied by 1.1% carbon 13. Thes isotopic peaks are particularly important for deducing the elemental composition of the molecule and its pieces displayed in the mass spectrum. Elemental compositions can also be determined from the exact mass of the peak, but the necessary high-resolution mass spectrometer is less commonly available. The measure spectra of these compounds contained additional peaks (not shown) due to the "Background" in the instrument arising from compounds desorbing from the walls of the instrument or leaking in from various sources. To avoid confusion, such a "background spectrum is usually run before the sample is actually introduced into athe instrument. Such a spectrum is shown as Unknown 4. Can you identify any of the components? Unknown 1.4 m/z Int. 100. 14 4.0 16 17 18 20 0.3 28 100. 0.8 1.0 5.0 0.8 32 23 34 40 2.0 1418 0.10

Answer 1

The given mass spectrum shows the base ion peak (most intense peak) at m/z 28. The peak at m/z 28 corresponds to the fragment C₂H₄. Therefore, the compound contains a C₂H₄ fragment. The compound also shows an intense peak at m/z 32. A peak at m/z can correspond to molecular oxygen, i.e, O₂. Therefore, the given molecule possibly contains C₂H₄ fragment and another fragment that can ionize to generate O₂.