Exploring Infrared SpectroscopyThis experiment explores some features of infrared spectroscopy and intro-duces you to the use of the technique in identifying unknown compounds.Organization of the ExperimentBecause of the limitations on the infrared spectrophotometer, you will do thisexperiment in teams of three. Because most of you are in labs with three stu-dents on a bench side, this makes a logical team. Each team will have 15-20minutes to use the spectrophotometer. During that time your lab instructorwill demonstrate the infrared spectrometer and run three samples for you.When you are not working in the instrument room, you can be using the com-puters in the Chemistry Computer Lab to examine spectra and work on iden-tifying your unknown sample as well as describing the important features ofseveral other compounds (Part 4).Part 1. Identifying an UnknownExamine each of the four spectra on pages 3 and 4. On page 1 of the ReportForm you will find the structures of four different molecules. Match the mol-ecules and spectra and explain your reasoning in each case.Part 2. Spectra of CHCl3and CDCl3The tetrahedral molecule chlo-roform, CHCl3, has a C—Hbond that has a characteristicstretching vibration around2900 cm-1. The H can bereplaced by a deuterium atom togive CDCl3. Recall that theatomic weight of H is 1.008,whereas a D atom is twice as heavy; it has an atomic weight of 2.014. Yourinstructor will run the spectrum of one of these compounds for you, and thespectrum of the other will be posted in the instrument room and in the labo-ratory. Examine these spectra and answer the questions on page 2 of theReport Form.Part 3. Spectrum of a Packaging FilmPackaging film, the transparent film you use in the kitchen or around thehome — Saran wrap, plastic baggies, “cellophane”—is made of organic mol-ecules. Small molecules are joined together to produce polymers, and the poly-mers are fashioned into various materials such as the polyethylene squeezebottles we use in the lab. Each team will bring a piece of packaging film to laboratory and willobtain the infrared spectrum of the film. Spectra of different film will be post-ed in the instrument room and you will use these to attempt to identify yourunknown film. Write up your results on page 3 of the report form.Chemistry 112 Laboratory: Infrared Spectroscopy—Experimental Directions Page 75Because of the limita-tions on the infraredspectrophotometer, youwill do this experimentin teams of three.Because most of you arein labs with three stu-dents on a bench side,this makes a logicalteam. As you wait yourturn with the spectrom-eter, you can work onthe other parts of theexperiment (Parts 1 and4). You should be able tocomplete almost all ofthe work during the labtime.HCClClClDCClClClChloroformDeuterochloroformREMINDEREach team will bring asmall piece of packagingfilm — 2 inches square— to lab. This can be apiece of a sandwich bag,Saran wrap, or anyother transparent film.Be sure to record thesource and brandnameof your film!Revised: March 2001Part 4. Connecting IR Bands with VibrationsOne feature of the Saunders Interactive General Chemistry CD-ROM is themolecular modeling software. There are hundreds of molecules whose modelsare in the CAChe folder on the CD. Inside of that folder you will find a fold-er labeled MODELS and inside of that a folder labeled INFRARED. Inside ofthat folder are the models of 19 molecules or ions whose spectra have beencalculated using the CAChe software (as we have done for SO2in Figure 2 inthe introductory material). To examine a spectrum, proceed as follows:a) Double click on the icon for a molecule in the INFRARED folder. The filewill open in the Visualizer program. b) When the model appears on the screen, go to the ANALYZE menu andthen choose VIBRATIONAL SPECTRA. c) The vibrational spectrum will appear on the screen. You can deepen andwiden the display by holding the mouse key down on the small square atthe right hand end of the horizontal axis (just above the 0 marking).d) The main bands in a spectrum are denoted by small triangles (▲). Click ona triangle, and blue arrows will be superimposed on the model, the arrowsshowing the movement of atoms in the vibration that gives rise to thatband. Part 5. Mystery CompoundsIn this portion of the experiment you and your team will run the spectrum ofan unknown compound and attempt to identify it. Results are summarized onthe Report Form.Chemistry 112 Laboratory: Infrared Spectroscopy—Experimental Directions Page 76Revised: March 2001Note: This portion ofthe experiment can bedone at another time.For an illustration ofthe connection of thespectrum with thevibrations in the mole-cule see Figure 2 onpage 3 of the introduc-tory material.Note: The calculated IRspectrum on the CD-ROM can only be ob-served on the Macin-tosh computers. Usethe new iMac computersin the Chemistry Lab.Spectra for PART 1 — Identifying an UnknownUnknown AUnknown BChemistry 112 Laboratory: Infrared Spectroscopy—Experimental Directions Page 77Revised: March 2001Unknown CUnknown DChemistry 112 Laboratory: Infrared Spectroscopy—Experimental Directions Page 78Revised: March