ANALYTICAL APPROACH ences in ΤΊ can cause the novice to make serious errors when reporting quantitative data. The T\ of a nucleus is affected not only by the atoms bound directly to it, but also by surrounding paramagnetic species (i.e., oxygen or iron in whole blood cells). Similarly, T-i values for different nuclei in the same molecule can vary widely if only one region of the molecule is bound or re stricted in its mobility.
polyiriers
k
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times are zero. In 2D NMR spectrosco py, the evolution-mixing period is used to perform spin gymnastics on inter acting nuclei. The second dimension is generated by sampling this interaction as a function of time in exactly incre mented times, ii. Fourier transforma tion in both time domains (Î2 and ii) then gives the 2D NMR spectrum. Three-dimensional NMR spectroscopy develops by adding a second evolutionmixing period and sampling it as a function of a third time, ta. The only requirements for successful multipledimension NMR spectroscopy are the interaction of the two nuclei of interest through one or two of the NMR parameters discussed above and selection of the appropriate spin gymnastics in each i 2 and Î3 to demonstrate these interactions. For example, MRI is a type of multidimensional NMR spectroscopy in which field gradients are changed during ti and (3. The correlation spectroscopy (COSY) technique is a 2D experiment that relies on the spin-spin coupling between two nuclei. Figure 2 shows the proton COSY spectrum of a colon tu-
Multidimensional NMR
Sound and Vibration Damping with Polymers
N
ever before has a book on vibration damping contained so much information from very different specialties. Empha sizing the state of the art, this new volume looks at damping materials from the view points of polymer scientists, physicists, and acoustical engineers. Presenting the viewpoints of both science and engineering, this modern text examines blends and interpenetrating networks for their ability to damp over broad temperature and frequency ranges. Background material is pre sented, as well as information on fillers, plasticizers, additives, new instrumentation, and theory. With 25 chapters, this unique text cov ers these topics: • definitions and concepts • dynamic evaluation • acoustic attenuation • polymeric materials
A better separation of species detect able by NMR spectroscopy is often achieved using multidimensional spec troscopy (2D and 3D). Although the basic concepts of these methods are rel atively simple, implementation can be complicated. An excellent introductory article on 2D NMR spectroscopy by Tom Farrar has appeared in this JOURNAL
(2).
Two-dimensional NMR spectrosco py can be defined using the following time domains: preparation, evolution (ii), mixing, and acquisition ((2). Onedimensional NMR spectra are ob tained when the evolution and mixing
J
CHjr™CH3 -
CH2—CH3
• vibration damping
• advanced materials The treatment is well balanced, offering mate rial needed in industry, government laborato ries, and academia. Authors are drawn from among the international leaders in the field. Robert D. Corsaro, Editor, Naval Research Laboratory L. H. Sperling, Editor. Lehigh University Developed from a symposium sponsored by the Divi sion of Polymeric Materials: Science and Engineering of the American Chemical Society ACS Symposium Series No. 424 469 pages (1990) Clothbound ISBN 0-8412-1778-5 LC 90-325 $99.95 0
•
R • D • Ε • R
F • R • 0
•
• CHg—CH3
2.6
2.4
1.2
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0.8
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Aromatic
7.0 6.5 6.0
1.0
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5.5
5.0
4.5 4.0
3.5
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5CH2 2.5 2.0
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1.5
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American Chemical Society
Distribution Office, Dept. 68 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE
800-227-5558 (in Washington, D.C. 872-4363) and use your credit card!
Figure 1. Proton NMR spectrum at 360 MHz of ethylbenzene, 0.1 % in deuterochloroform. Insets are expansions of the multiplets for the CH3 and the CH2 moieties to illustrate scalar (J) couplings: The CH2 and CH3 resonances are split into multiplets by the J coupling between them. Coupling to the three protons of the CH3 group results in a quartet structure for the CH2 resonances, whereas the two protons of the CH2 group result in a triplet for the CH3 resonances. The chemical shift (δ) is the frequency (with respect to an internal standard, in parts per million relative to the frequency of the spectrometer) characterizing the particular proton species. For further explanation of these parameters, see Reference 1. (Courtesy of J. K. Saunders, NRC, Canada.)
854 A · ANALYTICAL CHEMISTRY, VOL. 62, NO. 15, AUGUST 1, 1990
