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Interpretation:
The reason for the statement “The mass spectrum of 3-methylpentane has a peak of very low relative abundance at
Concept introduction:
Mass spectrometry involves formation of ions in a mass spectrometer followed by separation and detection of the ions according to mass and charge.
The mass spectrum is a graph with mass (
One of the highest value m/z may or may not represent the molecular ion, that is, the ion with the formula weight of the original compound. When present, the molecular ion is usually not the base peak because the ions from the original compound molecule tend to fragment, thereby resulting in the other m/z peaks in the spectrum.
Small peaks having m/z values 1 or 2 higher than the formula weight of the compound are because of 13C and other isotopes.
Molecular ions formed by EI mass spectrometry are high-energy species and these are called radical cations because it contains both an unshared electron and a positive charge. Fragmentation of molecular ion means that a complex molecule is broken into smaller molecules and these fragments can undergo more breaking and so on.
Cleavage of a single bond produces a cation and a radical. The cation can be detected using positive ion mass spectrometry and because the radical is not charged, it will be undetected.
Chain branching or cleavage of a single bond at branch points will occur such that the carbocation formed is more stable. In simple words, the stability of carbocation determines the fragmentation pattern.
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Chapter 9 Solutions
Organic Chemistry, 12e Study Guide/Student Solutions Manual
- Following is the mass spectrum of an unknown compound. The two highest peaks are at m/z 120 and 122. Suggest a structure for this compound. (Data from http://webbook.nist.gov/chemistry/.)arrow_forwardQ.5. What is the most likely molecular formula of a compound with m/z of 101 for its molecular ion, and m/z of 30 for its base peak in its EI mass spectrum. Write two isomers of this compound (more isomers are possible).arrow_forward2-Methylpentanal and 4-methyl-2-pentanone are constitutional isomers with the molecular formula C,H,,0. Each shows a molecular ion peak in its mass spectrum at mlz 100. Spectrum A shows significant peaks at mlz 85, 58, 57, 43, and 42. Spectrum B shows significant peaks at mlz 71, 58, 57, 43, and 29. Assign each compound its correct spectrum. `H 2-Methylpentanal 4-Methyl-2-pentanonearrow_forward
- 1 (c) 2-Methyl-3-pentanol reacts with PCC to form compound F. (i) Draw the structure of F. (ii) In the mass spectrum, identify the m/z value of the molecular ion peak for compound F. (ii) Fragmentation of radical cation F exhibits two fragment ion peaks at m/z 57 and m/z 71. Propose the structures of these two fragments. (iv) Draw the resonance structure for each of the cation in (iii).arrow_forward8. a) Use the mass spectrum to determine the identity of the halogen atom (X) in the following molecular formula. 100 - C3H5XO2 80- 60 40 20- 152 154 20 40 60 80 100 120 140 160 180 200 m/z Relative Intensityarrow_forwardPropose a molecular formula for a compound that has one degree of unsaturation and a mass spectrum that displays a molecular ion signal at m/z = 86. Complete the molecular formula C₂HNcOd by entering the numeric subscripts below (enter "O" for any element that is not in the molecular formula, d#0). # of C atoms (a): # of H atoms (b): # of N atoms (c): # of O atoms (d):arrow_forward
- The molecular ion peak in a mass spectrum of compound W appears at m/z = 107. Predict the molecular formula of compound W. (Hint: Compound W contains a heteroatom, not only carbon and hydrogen).arrow_forwardPredict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds. (a) 2-methylpentane (b) 3-methylhex-2-enearrow_forwardThe two mass spectra below correspond to two isomers of C13H20O. Match the spectrum with the compound and explain your choice.arrow_forward
- Propose a molecular formula for cedrol, an alcohol found in cedar oil. Cedrol has three degrees of unsaturation and a molecular ion in its mass spectrum at m/z = 222.arrow_forwardPredict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds. (a) cyclohexyl isopropyl ether (b) tert-butyl propyl aminearrow_forwardPropose a molecular formula for rose oxide, a rose-scented compound isolated from roses and geraniums, which contains the elements of C, H, and O, has two degrees of unsaturation, and a molecular ion in its mass spectrum at m/z = 154.arrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning
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