Basic NMR Spectroscopy NMRTerminology The laboratory vs. rotating frame of reference Response of spins to pulsed magnetic field NMR pulse sequences The Fourier transform Measuring relaxation times 8. Imaging using the hack projection 9. Slice selection in MRI 10. Partial saturation Fourier transform imaging sequence I I . Imaging data and the iwo-dimensionalFourier transform 12. Additional MRI pulsesequences 13. l'hr magnetic resonance image 14. List oi rquations 15. Lirt of rrnding materials 1. 2. 3. 4. 5. 6. 7.
The package is suitable as a stand-alone teaching package or as part of a lecture presentation. Although the package was intended to introduce the principles of MRI, the first half is suitable for teaching the basics of modern NMR techniques. ~ a c k a e ehas been used at RIT at the underThis teachine-. graduate and introductory graduate levels with much success. Students may use the package a t RIT in our departmental computer room or check it out for use a t home. Students have found the seauences describine - the soin echo and two-dimensional Fourier transform imaging techniques esneciallvuseful. Thev have commented that the material is i k m e d i a k y comprehendible on viewing the sequences. From the instructor's point of view the time needed to explain the dynamic processes of MR is significantly reduced. The menu selection of topics allows the viewer to treat the material as a formal course by viewing topics in order or as a review by viewing individual topics. creation of this software was supported by the Rochester Institute of Technology under its productivity grant program. This software package is entitled "The Basics of NMR Imaging, A Computer Based Teaching Package" and is available from RIT Instructional Media Services for $50.
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EmerllencY Response J. Shofstahl, D. Jencen, G. Chansa, and J. Hardy The University of Akron Akron. OH 44325
Safetv in the chemical laboratorv is alwavs a concern. precautions to take ~ t u d e n i a a r einstructed as to the as to ~rotectiveclothine and safe handline of chemicals. ~ h e n ' s ~ e c i aprecautions l are required, this is also noted. However. i t is not alwavs oossible to nresent much information as to health hazids'and procedures in the event of a laree soill or fire. system has been developed t o provide information on over 1900 chemicals, mixtures, and general material classes in a form that is easy t o retrieve -and use. Students can rapidly locate hazard-related information on chemicals they will be using with little or no instruction. The system contains a range or information for each material where available and appropriate.
A
Name and up to four synonyms Formula Description Chemleal and storage incompatibilities Chemical Ahslracta Registry number (CAS) NlOSH Remtryof Tonic Effects of ChemicalSubstances (RTECS) number Environmental Protection Agency (EPA) Hazsrdous Waste Codes Department of Transportation (DOT) Numbers and Guides National Fire Protection Association (NFPA) values for Health, Flammability, and Reactivity hazards. Physical properties including: weight, vapor pressure, melting paint, boiling point, flash point, explosive limits, and solubility. 648
Journal of Chemical Education
All information has been taken from the following standard sources on hazardous materials. NFPA No. 49-Hazardous Materials, 1975. DOT-P 58000.2-Hazardous Materials, Emergency Response Guidebook. 1980. DHEW ~ubiicationNo. 78-210-NIOSH Pocket Guidebook to Chemical Hazards, 1985. Federal Register, Vol. 45, No. 229. The student can locate a chemical based on names. formula, or registry numbers. Wildcards may be used tb locate materials based on oartial entries. Once an entrv has been identified, the data screen is displayed withalldaro pertainine to the chemiral. Svecific definitions for the NFPA haza& values and a compiete DOT Emergency Response Guide can be obtained with a single key stroke. The Emergency Response Guide gives the student a list of any health, fire, and explosive hazards and corrective actions they can take in the event of a spill or fire. A second benefit of the system is that i t provides a crossreference of the various reeistrv numbers assiened to a chemical. This should prove-usef;l to stockroom-personnel faced with the res~onsibilitvof hazardous waste dis~osal. The program is h i t t e n incompiled BASIC and runsonan 1BM PC (orcomvatible) withal least 512 K RAMand a hard disk containing at least 2.5 MB of free space. The system is distributed on either two 360 K 5 W n . disks or one 720 K 3'f2-in. disk. A copy of the system and the 63-page user manual may be obtained by sending $50 (to cover postage and duplication costs) to J. K. Hardy, Department of Chemistry, The University of Akron, Akron, OH 44325. Please specify the disk format desired.
An X-ray Diffraction Pattern Simulator Gonzalo Rodriguez and Silvlo Rodrfguez University of the Pacific Stockion. CA 95211 Most textbooks on experimental physical chemistry include the analysis of an X-ray powder diffraction pattern from which students determine the cubic lattice type and the lattice constant of a crystalline substance. The density of the substance is then calculated from these data (12-15). Currently, structural determinations by X-ray diffraction are highly computerized, and powder pattern photographs are verv ~" rarelv used. Because manv educational institutions donot have X-ray equipment avaiiable, usually each student is eiven a neeative or nrint of a film and asked to oerform c e h n calcu~atioos. here is a clear pedagogical val"e in the determination o f a cwstal structure hv this method, and the experiment is usualiy included in experimental physical chemistry rourses. Although powder patterns for all alkali halides are available in the literature (16), it is desirahle to be able to eenerate the X-ray powder diffraction pattern of a substancefrom a knowledge bf its density and cubic structure. This increases the variety of "unknowns" available for student usage and allows a comparison of the diffraction patterns of a substance hypothetically crystallizing in a simple (primitive), face-centered, or body-centered cubic lattice. We have develooed a microcom~uteraroeram that simulates X-ray powder diffraction for many substances and oroduces realistic spectra from the input of (1) the atomic or ?ormula weight o f t h e compound, (2) the density of the compound, and (3) the lattice type. The program, written in Microsoft BASIC Version 1.31, for execution on the Sanyo MBC-555 microcomputer, consists of 85 lines, including 10 remark statements, and can be easily converted for use on any other version of BASIC. The program calculates the ~
~
~
~. ~~
leneth of the edge of the unit cubic cell from the densitv and thetype of cubic structure. Then it determines interplanar s~acinasdhaf,where h, k, and I are the Miller indices. Angles bktween the planes and the diffracted X-ray beams are Ealculated from Bragg's law, nA = 2d,, sin 0 where twicallv the value of X is 154.18 Dm, the weighted average-&avelLngthof the copper Kol radiation doublets. Distances for the lines in the forward and backward reflection parts of the film are obtained by assuming the value of the effective radius of the film in the camera to he 57.23 mm. For the sake of simplicity no attempt was made to make the spectrum more realistic by curving the lines around the collimator hole and beam stop. However, we have used the wavelengths of the doublets Karl = 154.056 pm and Ka2 = 154.439 om to orovide well-resolved doublets in the back reflection region. In a cubic lattice of unit cell dimension a. the interolanar distance is d,, = a/(h2+ k2 + P)ln
(2)
and the angles at which the (hkl) planes diffract are given by
+ +
+
sin28= (X2/402)(h2 + k2 1')
(3)
where h2 k2 12mustbe an integer. Because the sum of the sauares of the Miller indices cannot have the values 7.15.23. . . . 28, 31,. .. , the corresponding lines will be missing in the spectrum of a substance crvstallizing in a cubic lattice. The presence or absence of all other lines is given by the structure factor F, which is obtained by summing the atomic scattering factors fi over all the atoms in a unit cell. Line intensities are given mainly by IFI2 (17).The structure factor can be expressed in terms of the Miller indices and coordinates (xi,
For a simple (primitive) cubic structure the atoms are located a t (O,O, 01, (a, 0, O), ... ,(a, 0, a), . ,(a, a, a); therefore,
..
+
+ ...+ ewchtr)+ . ..+ e2nchtktn)
Fhkl = 1/8f,(l ezSih
(5)
The value of the structure factor can be easily determined by taking into consideration that enri= cos nn i sin n?r.. and. ~~, because h, k, and 1are integers, sines of multiples of n are zero, while the cosines are equal to one. In a face-centered cubic lattice the atoms are located a t (O,O,O), (a, 0, O), . . . , (aI2, a, O), .. . ,(a, a, a!, and it can be shown that diffraction will be observed only if h, k, and 1 are either all even or all odd, making !PI2> 0. A body-centered cubic unit cell has atoms at (O,O, O), (a, 0, a), . . .,(al2, a12, a/2), and absences will be observed whenever the sum of h k 1is odd. In the program, values for the allowed sums of the squares of the Miller indices are contained in DATA statements for each cuhic lattice -.-. ~-~~~ ~ - - ~ Figure 4 shows the original film and a printout of the diffraction pattern of aluminum as obtained with an Olym-
+
+ +
~
oia NP dot-matrix orinter. This ~rinter.as most dot-matrix printers, allows a p;ogrammable n1216-in. forward line feed, which oroduces a minimum separation of 0.12 mm for the diffraction lines. Of course the program is not restricted to real substances, and any combination of formula weight, density, and lattice type providing an interplanar distance greater than 77.03 pm will produce a simulated X-ray powder diffraction pattern of the hypothetical substance. A listing of the program and accompanying instructions are available from the authors. Requests should include a stamped, self-addressed envelope.
Multiple-choice Self-lest James F. Nugent Salve Regina College Newport. Ri02840
Students taking beginning chemistry courses are often unaware of their lack of basic knowledge until it shows up in their first examination. The goal of this computer appication is to help chemistry students tent themselves and also be instructed. Specifically, I wanted to help students in a one-semester course in oreanic chemistrv to test themselves in the areas of reactions and nomenclature. I wrote a file called ALKENE.BAS in Advanced IBM Basic on an IBM PC with a Color Graphics Adapter and color monitor. The student who runs the file sees an alkene reaction question where the starting material and reaction conditions are given, but the product is a question mark. On the same screen the student sees five possible answers labelled "A" through "E". The program congratulates students who choose the correct answer and ins&cts them to go on to the next question. Students who choose an incorrect answer are given a brief explanation of why that specificanswer is incorrect and told to try again. After writine one or two other files on other oreanic functional groups, i realized that there were many pr&ramming steps that were indeoendent of the chemical subiect matter. I t was only necessaiy to delete all specific textual lines to obtain a file called SKELETON.BAS. As new text was added, it became "flesh and blood" on the skeleton and led to the creation of additional files. In this wav, 12 basic files were written on organic reactions and nomenclature. Each file contained from four to 10multiole-choice questions. The files were put together with a menu program so that the student could move between files at will. The SKELETON.BAS file can be used to generate multiple-choice questions in any field. Remark (REM) statements are placed at the Basic line numbers where text should be placed. The instructor can choose wrong answers that illustrate common student misconceptions in the specific subject areas. Then, these misconceptions can be cleared up by the wrong answer explanation screens. I modified SKELETON.RAS to allow a maximum of 25 questions per file and to permit the letters of the correct answers to be scrambled for-each new file. I have also included a blank menu programand adocumenration file saved in ASCII text called SKELWON.DOC to explain fully how to make selftest files from SKELETON.BAS. Copies of all the tiles t'or the IRM PC can be obtained from Project SERAI'H1.M. Literature Clted 1. Bww,
F. Chnin Struecur. ond
Cmfarmotwn of M~eramolsculas;Academic: New
York, 1982.
2. Odian. 0.P~incipleaof Polymorirolion, md ed.; Wiley: New York, 1981:h m p p . P.: Mmrill, E. W . Polymer Synfhe&: HWhigk Wepf: Heidelbeq, 1986.
3. Wehdi, F. W.; WirMin, T Intrrprefolion of Corbon-I3 NMR Spectra: Heyden:
F l g m 4. (A) The X-ray diffractionpowder spechum computer-simulated spsmum.
of aluminum: (6) the
.....
D!.n0.,d"hb ""u.F... ", ,O"R
C. Ed. NMR ond Moemmolecules; ACS Symp. Series 247: American Chemical Soeiaty: Washington, DC,.,l984.
I . Randall. J.
Volume 66 Number 8 August 1989
649
