pole moment. (Transfer can be either by printing the data file and re-entering the coordinates manually, or more conveniently by a file transfer program). The results, 4.89 D for the "cis", and 1.8 D for the "trans" conformations are realistic, while the energy difference provides a quantitative explanation for the expected predominance of the "trans" form. (The experimental dipole moment is 1.78 D (7).)Requirements for running these programs, an IBM-PC with 512 K memory and an 8087 coprocessor, are not excessive, while SERAPHIM programs themselves are available at nominal cost. Typical time requirements have been 2 h for a given conformation. Although we employed the SERAPHIM programs initially and found them to be useful, we have now switched to a faster and more convenient, although more expensive, program, PCMODEL from Serena Software2 (academic price $200). In addition to the results eiven bv the SERAPHIM disks, this program readily additional information, such as plots of enerw as a function of rotation about a bond. that permits the student easily to explore the details of conformational changes and rotational barriers. Figure 6 illustrates one type of information that can be displayed. This shows the variation in energy on rotation about the CH&-OCH3 bond. This program also gives a simple readout of the structural parameters of the conformation. Students find the data input easy and the entire exercise fast enough to permit extension to other molecules in a reasonable time period. This approach provides a useful linkage of experiment to theorv,as well asa valuableop~ortunitvLO link this material further to lecture topics deaiing with molecular conformations and theoretical chemistry. It is important to make clear the approximations and limitations of the calculations to show that they are not a replacement for experiment, but a guide and supplement.
Microcomputer Interfacing Programs Shahmkh Ghaffarl Mount Marly College Yankton, SD 57078 With recent emphasis on computer interfacing and automation of chemical techniaues and instruments it is inevitable for chemists, especialliin the field of analytical chemistrv. to overlook the application of computers and their place iiboth undergraduate teaching and research. To extend the capabilities of our instruments such as DBG Beckman spectrophotometer and Gow-Mac gas chromatograph and to introduce students to the applications and the advantages of microcomputers in analytical laboratories, Microcomputer Interfacing Programs were developed. These programs are designed to work with most instruments, and required no computer programming or electronic experiences. The package consists of three programs. The first program is desimed to work with spectrophotometers. In the first section-of this program students are able to scan for sample cell comparisons (in double-beam instruments) andlor find the maximum absorbance. Data are plotted on the screen as they are collected and the program finds the wavelength of maximum absorbance (Fie. 7). Then the snectrum and other information can be stor& on a disk an'dlor printed on a printer. Scanning can be done in two ways, automatically or Available from Serena Software, Box 3076, Bloomington, IN '47402.
Figure 6. -gy
Screen display from the FCMODEL (Serena) program. as a function of mtation about CH3-OCHs bond.
0
7 b
600
500
400
showing
300
Wavelength (nm) Flwe 7. Wavelengm scan for (a) sample cell comparison, (b) finding the wavelength of the maximum absotbance.
manually, from low wavelength to high wavelength or vice versa. Further scanning is possible using the same plot or selecting different conditions. The second part of the program is designed to collect data from the instrument through an A D for a set of standards and unknown(s). Data are collected and saved as both absorbance and percent transmittance. Results are tabulated, and the best fitted line is plotted. Also other statistical information such as slope, least-square line equation, etc., are presented (Table 1). This program is able to calculate the concentration of one or more unknowns using the same set of standards. If more than one unknown is run, average or separate values for concentration of unknowns can be obtained. Table of data, result of calculations, and calibration curve (Fig. 8) are printed on the printer. Also a simple interface circuitry for Spectronic-20 is available in the supplementary material. The second program, which is developed to work with a Gow-Mac gas chromatograph, also can be used with most other chromatographs. This program can be used to obtain a simple chromatogram for a single injection or to run standardlunknown solutions for a quantitative and/or qualitative experiment. In the latter case after initialization, which includes entering the operation conditions, the computer Volume 66 Number 10 October 1989
837
Table 1. C o l l ~ e Slgnal, d Statlrtkal, Data, and Conceniratlon of Unknown Wed Jun 29 3:39:22 PM Concentration mg/L
Data # 1
1
2 3 4
3
1
Std.
% Tranamiltance 90 70.3 60.3 30.2
5
10 Unknown's slgnal
1 Slope of line = -6.41 Conelallon coeniciem = -0.993 Y intercept = 93.2 Least-square line: Y = 93.2 (-6.41)X Std. Dev. for residuals = 3.58 Std. DBV.of slope = 0.54 Conc. of unk. X1 = 7.96 mg/L
42.2
+
loof
M n calibration c u r v e
0
0
2.5 5 7.5 Concentration ( m g / ~ )
10
Figure 8. Calibration curve. The unknown is marked with "r"
Table 2. Llrt of Peak Heights, Retention Times, Peak Names, and Operation Condnlons of Standard Mixture Solution
0
.5
1.5
i
2
Time (min) Figure 9. Chramatogams of (a) standard solution. (b) unknown Solution overlapped wilh standard solution. (c)u n k m solutim.
mu oec 03 3:04:10 PM Peak X
Height %
Rei. Time min 8 s
1 2 3 4 5
48 94 80 8 40
0:24 0:32 0:40 1:2 1:7
Outlat temp. = 155 'C Deteclor temp. = 170 OC BrMg c w e m = 160 mA Gas carrier = He Recording renge = 50 mV Sample size = 1.2 micro L Injection port = B
Comp. Name Methyl a1 Pmpyl a1 l~obutyle Namyl ai
Column temp. = 132 'C lnjenion temp. = 160 OC Polarity = Gas flow rate = 65 mLlmin Recordingtime = 2 mi"
draws axes of the chromatogram and waits for injection of the standard mixture solution. As soon as the injection is completed the computer is activated by pressing the "return" key. After the last component emerges from the detector and its peak is plotted, the operator has the option of either getting a copy of chromatogram (Fig. 9a) or repeating the process under the same set of conditions or a different set of conditions. Then the computer advises the operator to save the chromatogram for the next step. The peak heights and retention times are printed on the screen, and the opera-
838
Journal of Chemical Education
tor can type in the name of each peak. This information and other o~erationconditions are run off on the printer (Table 2). ~ e x the t unknown mixture solution is injected as described above for standard solution. The unknown chromatogram can be overlapped by a standard chromatogram for identification of unknown peaks (Fig. 9b) or can be plotted- senaratelv. In the former case. after the unknown Deaks are identified the unknown chromatogram is separated from standard (Fie. 9c). In either case the o ~ e r a t ocan r t. w.e in the name of each peak and run off a printed copy. The third oromam, which is designed for a conductivity . .. measurement experiment, after the initialization simply collects data from a conductance meter. This program use3 a set of standard solutions to plot a calibration curve and the best fitted line and then measures the conductance of unknown solutionW and calculates the concentration(sJ. An Apple lle microcomputer with 64 K memory wad t.111ployed for this project. The chart recorder output of instrument is used LO direct signals into a 12-bit analogue-todieital converter (. A D .) interface card (ADDlied Engineering c;.). To print the screen, a Grappler interface iard (0; ange Micro, Inc.) is used in conjunction with an Imagewriter printer (Apple Co.). A Timemaster I1 H.O. card (Applied Engineering Co.) is placed in slot #4 of Apple computer to print the date and time of experiment (optional).
+
The program is written in Applesoft Basic language. I t is very easy t o make any changes in these programs in order to work with other interface systems. A free copy of Microcomputer Interfacing Programs may be obtained by writing t o the author. These programs and three sample experiments, ones used to obtain the data presented here, are also available on disk for $12 (including manual).
Searching the Chemical Literature: An Individualized Librarv Exercise using a SERAPHIM
Give at least three names for your compound (i.e., generic, brand name, IUPAC, ete.), and cite the sources for your information, Give a complete citation for at least one paper on the synthesis of this compound, and attach a photocopy of the CA abstract to your pet a copy paper? report. Where and how could .you . ~.of the . Give a complete citation for a paper about the pharmacological activity of this eompound. Where could you get a copy? Attach a copv .. of the ahstract to your rewrt. Using the Science Citation Index (SCI) find out how many times the pharmacology article was cited in 1964. Give a full citation for at least one pamr that cites the phmacolow -.article, and attach a photowpioithe SCZ page to ;our report. (For extracredit, obtain copies of both your cited papers and write a 1-page summary of their contents. Attach the original papers to your report also.)
After a brief library orientation, the students were allowed eight weeks t o complete the report, including time necessary for interlibrary loans t o be processed. University of Wisconsin-Parkside The amount of library time actually spent on a typical 3Kenosha, WI 53141 page report ranged from about 5 h to more than 50 h; the Organic chemistry students are often introduced to the averaee time was between 10 and 15 h. About half the stuchemical literature through exercises in their laboratory dengworked on the extra credit assignment. The students manuals; these exercises generally consist of a series of unreenjoyed working with the program and worked hard a t getlated questions that briefly expose the students to a large ting a compound with "good" activity, then expended serinumber of chemistw sources. However, these exercises do ous effort working on a good report. They were especially not really resemble a t r u e literature seareh, and the students attracted hy the iaea of &signing their own molecule. tend to share data, minimizing their actual exposure to the In the initial run of this exercise the Design-A-Drug proliterature. Later courses that require detailed literature gram generated a numher of compounds with no literature searches also need t o review the basics. references, yet high reported hiological activity. The probSeveral criteria can be established for a better introduclem was traced 6 the manner in which the promam calcutory exercise. I t should provide each student with a series of lates activity: it is a weighted calculation based on substituauestions about a uniaue com~ound.so that students need ent position and structure but is not directly related to tb use the literature i n a manner moie consistent with typireported activity. Modifications to the program were made cal research ~roblems.Such individual, but related.. assignthat minimized this problem; we were also able to speed ments would avert the pooling of specific information to student use of the program with code changes tbat facilitatsolve auestions but would allow the students to help each ed data retention between trials and eliminated timed waits. other &th general research techniques if necessary and a t A few other problems appeared as well. In their eagerness the same time would give the students a sense of having a to get a "good" compound, students often duplicated each coherent, realistic prol&m tosolve for themselves. However, other's results; instructor review of the compounds chosen the problems assigned should not be toodifficult since these minimized this. Students also sometimes wanted to count students are just beeinnine their serious study of chemistry for extra credit articles in foreien lan~uapestbat they could -.~~-~~~~ of the and have not previously been exposed to the chemical literanot read, but the student summat$ ( n i t a ture a t all. Enelish abstract) was reauired for any extra credit. This paper reports an individualized literature exercise Evaluation of'the student work was based on complete that fulfills these criteria and has been used successfullv for and reasonable answers to the questions, judged with referseveral classes of organic chemistry laboratory student;. ence t o the photocopied materials included. Summaries for Molecules for each report were generated by the students extra credit could usually be evaluated in comparison with themselves, using the SERAPHIM program i ) e s i g n - a - ~ r u ~ the abstract of the pape; in question and were counted less (SERAPHIM Disk IR 701). 1)esign-a-Drug investigates the heavilv if they merely copied an abstract or other sections of pharmacological activity of a number of tricyclic aniidepresa pap& writing stile, grammar, spelling, and effort were sants by allowing the operator to build u p a specific molecule also given some weight. The exercise has been found narticularlv suitable for an on a tricyclic base; variations in substituents can be made a t ---. ----five different positions, and for each specific molecule made organic chemistry course since i t relates t o organic synthesis the Dromam returns a calculated bioloeical activitv. Thus of comoounds relevant t o the "real world" and allows the the operator can examine a large number of molecules for student t o relate biological activity t o molecular structure. activity and build up a body of information from which Copies of the program can be obtained from the author, structure-activity relationships can be determined. For this along with a more detailed discussion and a list of successful librarv exercise. each student was reauired to use the proreferences. g r a m t o design' a molecule for investigation that had an activity of a t least 75 on the promam's rating scale of 1-100. This activity waschosen in oidei to minimize false starts for the students; the hope was that any compound with activity Huckel Molecular Orbitals that great would b e a well-known, easily found compound John J. Farrell and Harry H. Haddon with commercial application and many references. Franklin and Marshall College The students were asked to answer nine questions about Lancaster, PA 17604 their compounds: G. Lynn Carlson and Erlk Womeldorl
~
~
~~~~
.
~
-
What is the structure of your pharmacologically active compound? What type of biological activity does it have? What is the correct numbering system for the ring system in your compound? What is the CA registry number far this eompound?
Program Huckel Molecular Orbitals (Version 2.3) calculates energy eigenvalues, eigenvectors, pi-electron charge densities, and pi-electron bond orders for conjugated and aromatic molecules using the assumptions of simple Huckel molecular orbital (HMO) theory. Each of these parameters Volume 66
Number 10 October 1989
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