Spectroscopy and the Electromagnetic Spectrum

Mass spectrum of 2-methyl-3-pentanol, Practice Problem 12.3. 

Solution 2-Methyl-3-pentanol, an open-chain alcohol, has = 102 and might he expected to fragment by a cleavage and by dehydration. These processes would lead to fragment ions of m/z = 84, 73, and 59. Of the three expected fragments, dehydration is not observed (no m/z = 84 peak), but both possible a cleavages do take place (m/z = 73, 59). 

Loss of C3H7 (M - 43) by alpha cleavage gives a peak of mass 59. 

Problem 12.4 What are the masses of the charged fragments produced in the following cleavage pathways  

Methods other than electron bombardment (EI-MS) can be used to obtain mass spectral data. In chemical ionization-mass spectrometry (CI-MS), the sample is sprayed with a pre-ionized gas such as methane or ammonia that causes the sample to ionize by electron transfer or proton transfer from the gas to the sample. Because the molecular ions produced by this technique are less apt to undergo fragmentation, the ability to obtain the molecular mass (and therefore the molecular formula) of the sample is enhanced. 

Forensic science is the application of science for the purpose of answering questions related to a civil or criminal case. Mass spectrometry is an important tool of the forensic scientist. It is used to analyze body fluids for the presence and levels of drugs and other toxic substances. 

It can also identify the presence of drugs in hair, which increases the window of detection from hours and days (after which body fluids are no longer useful) to months and even years. It was employed for the first time at an athletic event in 1955 to detect drugs in athletes at a cycling competition in France. (Twenty percent of those tests were positive.) Mass spectrometry is also used to identify residues of arson fires and explosives from post-explosion residues, and to analyze paints, adhesives, and fibers. 

Cosmic rays 7-rays X-rays Ultraviolet light Visible light Infrared radiation Microwaves Radio waves NMR 

The various kinds of electromagnetic radiation can be characterized briefly as follows  

Infrared, ultraviolet, and nuclear magnetic resonance spectroscopies differ from mass spectrometry in that they are nondestmctive and involve the interaction of molecules with electromagnetic energy rather than with an ionizing source. Before beginning a study of these techniques, however, let s briefly review the nature of radiant energy and the electromagnetic spectrum. 

Multiplying the wavelength of a wave in meters (m) by its frequency in reciprocal seconds (s ) gives the speed of the wave in meters per second (m/s). The rate of travel of all electromagnetic radiation in a vacuum is a constant value, commonly called the speed of light and abbreviated c. Its numerical value is defined as exactly 2.997 924 58 x 10 m/s, usually rounded off to 3.00 X 10 m/s. 

Just as matter comes only in discrete units called atoms, electromagnetic energy is transmitted only in discrete amounts called quanta. The amount of energy e corresponding to 1 quantum of energy (1 photon) of a given frequency V is expressed by the Planck equation 

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Visible light, X rays, microw aves, radio waves, and so forth, are all different kinds of electromagnetic radiation. Collectively, they make up the electromagnetic 

Which is higher in energy, EM radio waves with a frequency of 1.015 X 10 Hz (101.5 MITz) or visible green light with a frequency of 5 X 10 llz  

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The analyzer is an electrically grounded tube that detects the molecules by velocity. Spectroscopy and the electromagnetic spectrum (Section 12.5). 

As with UV-vis spectroscopy, IR and NMR spectroscopy are based on the interaction of electromagnetic radiation with molecules, whereas MS is different in that it relies on high-energy particles (electrons or ions) to break up the molecules. The relationship between the various types of spectroscopy and the electromagnetic spectrum is shown in Table 28.1. 

Spectroscopy and the Electromagnetic Spectrum Infrared Spectroscopy Interpreting Infrared Spectra... 

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