Long before I began teaching the undergrad orgo labs full-time, I was a TA for this course when I was a chemistry graduate student at UIC. At the time, there were few analytical techniques available for the characterization of organic molecules: no melting point apparatuses, no IR, no TLC and a sporadically functional GC with an unbearably slow analog plotter. A typical synthesis lab was often concluded by the students proudly shoving a yellow powder at me exclaiming, “See, I did it.” Sadly, I would acknowledge their accomplishment with a solemn nod, after which they would chuck their powder into the waste container with a strange jubilation. What was the point, I wondered. That yellow powder could have been anything. After about three years as a teaching assistant for this course, I was shocked one day when I found an infrared spectrometer in what is now the instrument room. I couldn’t believe we weren’t using this equipment in our labs. When I was hired as the full-time instructor, I made utilizing the IR my first priority. Of course, I quickly realized why this technique had been left by the wayside for such a large class: time. Time training TA’s and students, time creating instructional handouts, and time maintaining the spectrometer were all factors, but the time that it took students to acquire a decent spectrum was the most formidable challenge of all—primarily because of the difficulty students had with sample preparation. For liquid samples, students sandwiched a thin film between two NaCl plates. After the tenth plate was ruined by accidentally washing with and thereby dissolving in water, we switched to disposable PTFE cards. These worked well enough, but it was difficult to get spectra of volatile samples.

Solid samples had to be ground with anhydrous KBr and pressed with a die into a transparent disc. While seemingly straightforward, a number of conditions had to be met precisely right in order to obtain a disc of sufficient transparency and with a high enough sample concentration to acquire a spectrum in less than 5 minutes. The tension was palpable during these labs, especially when time was running short and the line for the IR wound outside the instrument room like a snake threatening to choke the sanity out of student and TA alike.

I’m happy to say, those days are over. The attenuated total reflectance (ATR) accessory, which I have fought to acquire since I began teaching this course, has arrived thanks to the differential tuition money that was made available to the Chemistry Department this year. After several tedious hours of tuning, aligning and swearing, the Pike Technologies GLADiATR was successfully installed. Then came the time of reckoning. After acquiring 64 background scans, I nervously applied a small amount of solid acetanilide to the 2 mm2 diamond crystal, lowered the pressure clamp and then turned the clamp dial clockwise until the pressure tip had pressed the solid into the diamond at 40 pounds of force. I clicked the scan icon on the screen and one minute later I was looking at my first successful ATR spectrum. The results were amazing. The total acquisition time from start to print was 3 minutes—a far cry from the 20 minute average for the KBr technique. Could it really be this easy? After twenty or so spectra later, the answer was a resounding yes. I was ecstatic. It’s a great feeling to know that this technology will radically change how IR is approached in CHEM 233 and I am anxiously awaiting to see how it will be received by the CHEM 233 students this semester.

Please click here for a full-color version of the instructions for using the GLADiATR accessory.

Tags: IR, ATR

The latest spectra are now posted online.  The lidocaine specs look pretty good!!  The final product, lidocaine bisulfate, is not very soluble in CDCl3, which is why some of you may have observed cloudy NMR sample solutions.  The book uses dimethyl sulfoxide (DMSO) for the NMR sample, which is much more polar and better able to dissolve your final product.  We don't have any DMSO currently, so CDCl3 will have to do; Navid's spectra turned out great in CDCl3 anyway.  Just be aware that the chemical shift values (ppm) for each proton signal will be slightly different than those reported in your textbook since chemical shift is solvent dependent.

Tags: NMR, Lidocaine, CDCl3, DMSO

The slides for Friday's (Feb. 15) lecture are now posted. Also, I updated the slides with each student's synthetic target assignments for Project Two. Plan your syntheses so that you will obtain approximately 200 mg of product. Because deciding on a recrystallization solvent system can be time consuming, I will tell you what system works best for the final product: water/ethanol.

Tags: 333, LFER, Hammett

NMR spectra for CHEM 333 will be acquired by Maria or Brooke each week. These spectra are later processed with iNMR and saved as a pdf file, which will be posted on this website. Each student is responsible for downloading and printing their own spectra each week. If you would like your spectra reprocessed, expanded, etc., send me an email and I'll get right on it. Free versions of iNMR are available (MAC only). If you'd like to upload your own data from the server and process it yourself with iNMR, stop by my office and I'll show you how.

All of your 1H-NMR spectra for benzocaine looked excellent. Great job on your Fischer esterification. We'll discuss the interpretation of 1H-NMR in class on Friday. See you then.

Tags: 333, NMR