Principles of Fourier-transform Nuclear Magnetic Resonance J. W. Blunt
University of Canterbury Christchurch, New Zealand
Figure 2. A screen display from MOVlT
There are several aspects of the teaching of Fourier-transform NMR theory and practice which call for the illustration of dynamic phenomena. Examples of this are nuclear precession, the response of the nuclear magnetization to the application of an r.f. pulse, and the subsequent behavior of the magnetization during relaxation. These topics may he illustrated very effectively by means of microcomputer-generated animated graphics. A series of such illustrations has been constructed for presentation on an APPLE I1 system. In addition, a number of units have been incorporated which permit the observation, in an interactive manner, of the way in which variations in the molecular and instrumental parameters, such as relaxation times, pulse width and repetition rate, affect the appearance of the free induction decay (f.i.d.1 spectrum and the subsequently derived frequency domain spectrum. The range of topics covered is seen in Figure 4, which is the menu displayed to the user. A typical example is shown in Figure 5, where the effect of applyingan exponential weighting
PRINCIPLES of TT NMR F r e c e s s i o n i n l a b o r a t o r y frame Magnetisation i n r o t a t i n g frame $ ; p l i c a t ~ s n of E l axat Ion e c q u i s i t i o n of f . i . ? . ateady s t a t e ma4netlsation Suninibt i o n of n o i s y t-. i . d . s I o u r -i e- r r r a n r f o r m 1 i from i n v e r s i o n - r e c o v e r y F o i d baf:k Re ?elution-sensitivity enhanceme Q ul. + ~
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Figure 3. A screen display from ROTATION. Figure 4. Menu display of FT NMR program
about the two other axes using the paddle controls and halt the rotation or chanre the axis of rotation any time. Some of the seventeen mole&les for which shape tables have been constructed are methane, isobutane, n-butane, cyclopentane, cyclohexane, the decalins, norbornane, phosphorus pentachloride, and sulfur hexafluoride. A hond rotation oroeram. ROTATION. allows the user to view any of six conformers (in steps of 60 degrees) about the 2,3 hond in n-butane (see Fig. 3). Again, each of the conformers can he rotated manually about any of the axes. The molecule can also he rotated manually while the internal rotation is proceeding automatically. The internal rotation gives the illusion of the dynamical aspects of hond rotation. This internal rotation is achieved by modifying the shape table by inserting new molecular coordinates for certain atoms, before calling on the 3-D driver routine. There are several ways in which the material can be extended. Using the EDIT program molecules of particular interest to the instructor can he entered for display. Also using the technique of shape table modification, as in ROTATION, it should be possible to illustrate the dynamical aspects of chemical reactions in three dimensions. The programs described are written in Applesoft BASIC with machine language subroutines. An Apple 11+ with 48K, a DOS 3.3 disk system, and installed paddle controls are reauired. A disk with all the Droerams and molecular shaoe tables plus documentation aregvailable for $25. A chick or money order made out to L. A. Hull should be sent to the above address.
Figure 5. Example showing improvement in FT NMR spectrum by application of exponential weighting factor.
Volume GO
Number 2
February 1983
97
factor to the experimental f.i.d. spectrum in order to improve the signal-to-noise ratio in the transformed spectrum may be observed. The consequent loss of resolution is readily seen. Other values for the parameter S E may be used to give resolution enhancement. This seauence of units has been used effectivelv during .ectures i n J course ,,ti principle> and applicariona or Feuritr-transiurm UhlH trc,hniuuc. The students then use the program in their own time to obtain more experience of the way in which the variations in parameters affect the experimental spectra. A single-page list of instructions is provided
theinstruction sheet, are available from the author upon request. A check for $10, made payable to the University of Canterbury, should b- included.
Drawing of Ball and Stick Type Molecular Models with Hidden Line Elimination Hidehiko Nakano, Osamu Sangen, and Yoshitake Yamamoto Himeji institute of Technology Shosha, Himeji 671-22, Japan Some programs have been reported for drawing of molecular structures by microcomputers (1,4) but these programs do not eliminate hidden lines. therebv increasing the realitv of drawings. Preparation of a with lhidden line elimination according to the same algorithms as are utilized " with mainframe computers is difficult due to the limitation of memorv size and calculation soeed. We have develo~eda simplified algorithm for drawing ball-and-stick m o l e h a r structures with hidden line elimination, and oreoared a oro. . Cram adaptable r u low cost m i c n ~ c ~ m p ustw~ er m s . This vrunram. written in 11.2SI
