18%20Ch12 - CHAPTER 12 Mass Spectrometry, Infrared...

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356 CHAPTER 12 Mass Spectrometry, Infrared Spectroscopy, and Ultraviolet/Visible Spectroscopy Important Terms absorption band a peak in a spectrum that occurs as a result of absorption of energy. auxochrome a substituent that when attached to a chromophore alters the λ max and intensity of absorption of UV/Vis radiation. base peak the peak in a mass spectrum with the greatest intensity. Beer-Lambert Law relationship between the absorbance of UV/Vis light, the concentration of the sample, the length of the light path, and the molar absorbtivity. bending vibration a vibration that does not occur along the line of the bond. α cleavage homolytic cleavage of an alpha substituent. chromophore the part of a molecule responsible for a UV or visible spectrum. electromagnetic radiation radiant energy that displays wave properties. electronic transition promotion of an electron from its HOMO to its LUMO. fingerprint region the right-hand third of an IR spectrum where the absorption bands are characteristic of the compound as a whole. frequency the velocity of a wave divided by its wavelength. (It has units of cycles/second.) functional group region the left-hand two thirds of an IR spectrum, where most functional groups show absorption bands. highest occupied molecular the highest energy molecular orbital that contains electrons. orbital(HOMO) Hooke's law an equation that describes the motion of a vibrating spring. λ max the wavelength at which there is maximum UV/Vis absorbance. infrared radiation electromagnetic radiation familiar to us as heat. infrared spectroscopy spectroscopy that uses infrared energy to provide a knowledge of the functional groups in a compound. infrared spectrum a plot of relative absorption versus wavenumber (or wavelength) of (IR spectrum) absorbed infrared radiation. lowest unoccupied the lowest energy molecular orbital that does not contain electrons. molecular orbital(LUMO)
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Chapter 12 357 mass spectrometry provides a knowledge of the molecular weight and certain structural features of a compound. mass spectrum a plot of the relative abundance of the positively charged fragments produced in a mass spectrometer versus their m/z values. McLafferty rearrangement of the molecular ion of a ketone that contains a γ -hydrogen; rearrangement the bond between the α - and β -carbons breaks, and a -hydrogen migrates to the oxygen. molar absorptivity the absorbance obtained from a 1.00 M solution in a cell with a 1.00 cm light path. molecular ion (M) the radical cation formed by removing one electron from a molecule. nominal molecular mass mass to the nearest whole number. radical cation a species with a positive charge and an unpaired electron. spectroscopy study of the interaction of matter and electromagnetic radiation.
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This note was uploaded on 03/29/2010 for the course CHE 118A 118a taught by Professor Kent during the Spring '10 term at UC Davis.

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18%20Ch12 - CHAPTER 12 Mass Spectrometry, Infrared...

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