Unformatted text preview: .3 Two mass spectra are shown below. One spectrum
corresponds to 2-methyl-2-pentene and the other to 2-hexene. Which is which?
B+ = 41 F+ = 69 -mass 15 M+ = 84 C3 H C3C2C=C HHH
bond cleavage C3 H Cleavage occurs at the weakest bond, which is due to the stability of a resulting allylic radical cation. Resonance stabilization.
B+ = 55 - mass 29 F+ = 69 - mass 15 M+ = 84 C3C2C 2C=CC 3 H H H H HH
bond cleavage Fig. 12-7, p. 415 23 12.3 Mass Spectrometry of Some Common Functional Groups
Alcohols: Alcohols undergo -cleavage (at the bond next to the C-OH) as well as loss of H-OH to give C=C 24 Mass Spectral Cleavage of Amines Amines undergo -cleavage, generating radicals 25 Fragmentation of Carbonyl Compounds A C-H that is three atoms away leads to an internal transfer of a proton to the C=O, called the McLafferty rearrangement Carbonyl compounds can also undergo cleavage 26 12.4 Mass Spectrometry in Biological Chemistry: Time-of-Flight (TOF) Instruments Most biochemical analyses by MS use: - electrospray ionization (ESI) - Matrix-assisted laser desorption ionization (MALDI) Linked to a time-of-flight mass analyzer (See figure 12.9) 27 12.5 Spectroscopy and the Electromagnetic Spectrum Radiant energy is proportional to its frequency (cycles/s = Hz) as a wave (Amplitude is its height) Different types are classified by frequency or wavelength ranges 28 Oscillating electric field Fig. 12-11, p. 419 29 IR Theory Discussed on Board in Class Electromagnetic Radiation produce an oscillating...
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- Spring '08
- Mass Spectrometry, Molecular Ion, Mass Spectrometry and Infrared Spectroscopy, mass spectra, peak Peak, Mass Spectrometers