provocative opinion W(h)ither Organic Qual? J. W. Zubrick
Hudson Valley Community College, Troy, NY 12180 'I've got some good news and some bad news. The ~ m d newsis that thplahnrntnry gnadrs are all hi~herthis ypnr The had news 1 3 that the Increaseis all in the lnha eoneernmg identification of unlmowns."
It's not the pithiest good news-bad news joke ever written. I'm not even sure there's anv bad news in it. I am sure. however, of those grades. The organic unknowns are being correctlv identified at a sienificantlv. higher rate this vear than in past years. Ever the alert scientist, I searched for an explanation. Better students? No. The grades for other exercises didn't vary much from the past. You'd expect all the grades to improve. Better written materials? Again, why the improvement in only one class of experiment and not all? Better equipment? Come to think of it, the computer-controlled FTIR was installed last September, and it seems that all the students took advantage, not only of the more r a ~ i dFTIR scan over that of the dis~ersiveinstrument. b i t also of the built-in search libraries provided with the instrument. in an effort to match their unknown to an included standard spectrum. And match them, they did. The instrument, a Mattson Galaxy 2000, comes with three IR libraries: Environmental Protection Aeencv (EPA). Georeia Crime Laboratorv (GCL), and ~atGon';o&n 1 ~ 0 ~ - l , ; o n t a i n i na ~selectioh of soectra more suitable to the undereraduate oreanic laboraiory than the other two. After conversion of a transmission spectrum to absorbance (all spectral libraries supplied are recorded in absorbance mode), the appropriate library is searched and, by default, the instrument provides the top 20-a rogue's gallery as it w e r m f the best matches based upon a correlation coefficient (there are other selectable search criteria). The spectra of the three best matches, along with a n attenuated version of the student's sample are displayed simultaneously on the screen for comparison plotting. What does this do to-organic qualitative analysis? I can still tell students to distill their unknown liquids, a good practice in any case. But black furfural (yes, someone did this) matches about as well as the distilled (really!) and re-packaged benzaldehyde samples, taken from a year-old or so oDen bottle, are still benzaldehvde, air oxidation notwithstanding. I can still have them do the sodium fusion. But even without an exact match, if the first three "hits" are nitrobenzene. D-nitrotoluene. and o-nitrotoluene. how manv brain cefii does it take &conclude perhaps thkre's a nit& een and. ves indeed. a nitro e r o u ~in the samnle. So much Tbr a fi&ky wet-chkmical Gtroien test that'can't distinm i s h amines from nitriles from nitro com~ounds.The same might be said for the halogen tests. I can still tell my students they have to make a solid derivative or two and take the melting point to confirm the identity of their unknown, and, as it has heen pointed out, "get a chance to really learn the chemistry" of that unknown compound. But with a correlation u~rff~cient ofover
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0.900, peaks identified to fO.O1 cm-', and expanded-scale observations of what would have remained obscure features in earlier representations, how much confirmation does one need? I suomse helping someone s t r w d e to recrystallize an oil-fo-&ing phknghydrazone, orrecover a ~articularlvdiEcult urethane still has its merits, but the nature of ihe distribution of unknowns wonk necessarily guarantee that everyone gets these grand opportunities. Would i t be better to have the entire class diazotize pnitroaniline on the way to phenacetin (Tylenol) and experience and overcome the oil-forming tendencies of student preparedp-nitrophenol? Or would this be, as Pickering has pointed out, "mere cookbooking" ( I ) . As the new computer-controlled instrumentation appears in more a n d more undergraduate organic laboratories the rationale behind organic qualitative analysis will have to he re-thoueht. The Dresencc of readilv-available computer-searchage speetrh data bases para~els,in a rough way, the introduction of the electronic calculator, and presents us with many of the same problems and possible solutions. "My answer can't he wrong. . . . I got it off my calculator."
I have already seen correct identifications based upon the FTIR s ~ e c t r alibrarv l match. even when a Dre~aredderivative, apparently of Goor quaiity, had a meking point a t variance with literature values: or a microboiline t -.~ o i ndetermination, done too quickly and without correction, failed to conform to accepted values. Yes. The students should have learned to perform these techniques correctly; yes, perhaps they should lose credit for these poor results. But what, again, was the purpose of the exercise? To correctly identify the unknown. Recrystallization and boiling point determination could be taught elsewhere, no? "They should learn their times tables before we let them use calculators."
Perhaos so. The reeular seauence of oreanic laboratorv affords ;any opport&ities fo; students td'perform recry;. tallizations. microbo~line~ o i n tdeterminations. distillaz has tions, investigation of reiciions, and so on. ~ i m i t (2) students prepare isolate, and characterize the oxime of benzil as a microscale reaction in ordinary test tubes never once mentioning this is a classic organic qua1 reaction. The difference-the unknown is a known, and the entire class gets the experience. If our students have already learned the times table, what is the point of denying the use of calculators. In some instances, in fact, this denial would be contrary to the stated mission of many institutions. Members of the advisory committee of our Chemical Technology Program, all drawn from local industry, applaud our recent acquisition of an FTIR and have strongly suggested we upgrade t the "state of the art." some of our other e a u i ~ m e n to Should we then handiiap our students and the community by ins~stingthey not use the technolo~ywe have acquired? Volume 69 Number 5 May 1992
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"Why do we do these things? I don't know! It's aTradition!"-
...%ye,
the milkman.
I'm getting very close now to what I wnsider to be the most unsettling point in this entire discussion. Do we keep organic qual because it's really useful, or do we keep it because we've always had it? After nostine the basic onestion in the chemistrv forum on ~um'puserve,'the preli;ninary, meager unscieitific results are in and aooear to be more of the"When I was a bov we walked bar26ot to school in the snow-uphill botK wavs" ohilosonhv. rather than an embrace of the latest in teckmoiogy. he& reports stress that the easiest thing to do is to limit use of the state-of-the-art equipment by fiat, and that performing the qual scheme needs to be done just in case the other technolow is not available (Translation: the instrumentation is down.). With that in mind, perhaps we ought to re-introduce sections on learning the slide rule into the chemistry cnmcnlum, just in casethe calculator technology is not &ailable. (Translation:the batteries are dead.) Yes. I am aware that the introduction of calculators has not been without its own problems-the proliferation of extra nonsignificant figures and the investment of faith in the calculator result often to the exclusion of reasonamong them. Yet, we don't limit their use. We just try to
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warn our students not to fall into these traps. And, as far as I can tell, this Journal is in the forefront of pushing computers into all aspects of chemistry, routinely singing the praises of Hypertext and CD-ROMs as improvements over your basic &&book, with nary a thoughtas to what happens should the technology fail. So I don't wnsider an appeal to tradition to make the best of arguments for keeping things as they are. When the exnerimental seauence runs again. , we will have an FTNMR joining the F+IR (and perhaps soon, with a bit of oraver and luck. low-maintenance GC-MS). These instruments, computer-controlled, will have searchable data bases for organic unknowns. and. with nnerades in software, there isno reason to suspect that the generation of nossible structures directlv h m suectra will not become available, even for the less e-&ensiv; models. As for the organic unknowns, in the face of all this mntinely available analytical power, I'm going to try a different tack. Perhaps polyfnnctional single componnds and more mixtures of singly functional componnds to be separated, before spectral identification. And I'll use the wet chemical tests to c~nfirmthe functionality, mostly as an afterthought. Or not. And as this kind of instrumentation becomes more and more available we may all have to give serious thought to the double-edged question: W(h)ither organic qual?
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Literature Cited
'CornpuSewe lnc., 5000 Arlington Centre Blvd., Columbus, OH 43220. Once connected, type GO SCIENCE.
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Journal of Chemical Education
1. Pickenng, M. J. Chem. Educ. 1991,88,232. 2. Nimitz, J. 5. Ewerimants in Ogonle Chemiatw:Rentia-Hall: N w Jusey, 1992,p 273.
