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More than a thousand different chemical compounds have been isolated from coffee. Their structures were determined using various spectroscopic techniques.

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FIGURE 12-1 A representation of an electron-ionization, magnetic-sector mass spectro meter. Molecules are ionized by collision with high-energy electrons, causing some of the molecules to fragment. Passage of the charged fragments through a magnetic field then sorts them according to their mass.

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FIGURE 12-2 A representation of a quadrupole mass analyzer. Only ions of a certain m/z ratio will reach the detector; other ions with unstable trajectories will collide with the rods.

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FIGURE 12-3 Mass spectrum of propane (C3H8; MW 5 44).

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FIGURE 12-4 Mass spectrum of 2,2-dimethylpropane (C5H12; MW 5 72). No molecular ion is observed when electron-impact ionization is used. What do you think is the formula and structure of the M1 peak at m/z 5 57?

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FIGURE 12-5 Mass spectrum of hexane (C6H14; MW 5 86). The base peak is at m/z 5 57, and numerous other ions are present.

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FIGURE 12-6 Fragmentation of hexane in a mass spectrometer.

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FIGURE 12-7 Mass spectra of unlabeled samples A and B for Worked Example 12-1.

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FIGURE 12-8 Mass spectra for Problem 12-2.

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FIGURE 12-9 Mass spectrum of 2-pentanol.

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FIGURE Mass spectrum of triethylamine.

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FIGURE Mass spectrum of chloroethane.

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FIGURE Mass spectrum of 1-bromohexane.

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FIGURE Mass spectrum of butyrophenone.

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FIGURE Mass spectrum of 2-methyl-3-pentanol, Worked Example 12-2.

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FIGURE MALDI–TOF mass spectrum of chicken egg-white lysozyme. The peak at 14, daltons (amu) is due to the monoprotonated protein, M+H+, and the peak at 28, daltons is due to an impurity formed by dimerization of the protein. Other peaks at lower m/z values are various protonated species, M+Hnn+.

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FIGURE The electro-magnetic spectrum covers a continuous range of wavelengths and frequencies, from radio waves at the low-frequency end to gamma (y) rays at the high-frequency end. The familiar visible region accounts for only a small portion near the middle of the spectrum.

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FIGURE Electromagnetic waves are characterized by a wavelength, a frequency, and an amplitude. (a) Wavelength (λ) is the distance between two successive wave maxima. Amplitude is the height of the wave measured from the center. (b)–(c) What we perceive as different kinds of electromagnetic radiation are simply waves with different wavelengths and frequencies.

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FIGURE An infrared absorption spectrum for ethanol, CH3CH2OH. A transmittance of 100% means that all the energy is passing through the sample, whereas a lower transmittance means that some energy is being absorbed. Thus, each downward spike corresponds to an energy absorption.

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FIGURE The infrared and adjacent regions of the electromagnetic spectrum.

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FIGURE IR spectra of (a) hexane, (b) 1-hexene, and (c) 1-hexyne. Spectra like these are easily obtained from submilligram amounts of material in a few minutes using commercially available instruments.

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FIGURE The four regions of the infrared spectrum: single bonds to hydrogen, triple bonds, double bonds, and fingerprint.

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FIGURE C – H out-of-plane bending vibrations for substituted alkenes.

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FIGURE C – H out-of-plane bending vibrations for substituted benzenes.

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FIGURE IR spectrum of cyclohexanol.

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FIGURE IR spectrum of cyclohexylamine.

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FIGURE The IR spectrum of benzaldehyde.

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FIGURE IR spectrum for Worked Example 12-6.

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FIGURE The IR spectrum of phenylacetylene, Problem 12-9.

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The structure of human muscle fructose-1,6-bisphosphate aldolase, as determined by X-ray crystallography and downloaded from the Protein Data Bank, 1ALD.

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