Unknown Identification Reports

These instructions also appear in the Lab Manual section on" Laboratory Reports". The instructions below are similar, but take precedence.

The unknown identification report consists of several sections: 1) a Report Form cover sheet, 2) spectroscopic data, 3) qualitative analysis data (for some experiments), and 4) a written report section. Please follow all the instructions on this page.

Report Form Cover Sheet:
The Report Form for the experiment is found in the Lab Manual. If you choose not to use that form, you can construct a facsimile with your word processor. Draw (do not copy and paste a structure from the internet) an expanded structural formula for the identified unknown. Also, give both its systematic name and any synonym names. Remember to include the experimental and the temperature-corrected refractive indexes (with temperatures explicitly noted as superscripts). Be sure to cite references properly. See the Citation section in the Lab Manual.

Spectroscopic Data:
Draw the structure of your identified unknown on both your experimental IR and NMR (NMR only in Chem 318) spectra. In a clear and obvious way, label each important absorption on the spectrum with a structural feature of your unknown (see linked example). Make sure you use a pen that will show up clearly on the spectrum.

For NMR (Chem 318), include the complete calculation of the peak integration and splitting patterns. If you obtained the experimental spectrum from the Bruker 400 mHz NMR, remember there is an impurity peak at 3.4 ± 0.2 ppm.

Find the IR and NMR (Chem 318) spectra for your identified unknown from the literature -- either print or on-line source. The best sources for finding matches to your experimental spectra are the Aldrich compilations in the library and the SDBS on-line site. (Do not use the NIST IR's -- most are taken in the gas phase -- your IR's are liquid phase. For any database, try to find the IR spectrum as a liquid, not in CCl4 solution.) Cite the source of your literature spectrum directly on the spectrum. If your experimental and literature spectra don't substantially match, peak for peak, especially in the fingerprint region, you have not identified your unknown.

Qualitative Analysis:
At the end of the semester in CHEM 315, you will perform qualitative analysis tests on your unknown. (Qualitative analysis is not part of the 315 Spectroscopy Unknown experiment.)

Fill in the blank cells in the table in the manual. Give the test result (positive or negative) and brief statement of your experimental observation (e.g. yellow ppt.; no color change). This table will be turned in with the report.

Prepare a separate page of balanced chemical equations showing the reactants and products for a positive test. (Organic compounds are to be shown as structures, not formulas.) This page should be a continuation page in your lab notebook. If your unknown gave a positive test, use the unknown compound structure (now identified) for the equation; if your unknown did not give a positive test, choose one of the known compounds that tested positive to illustrate the reaction. Every qual test must be included on this page.

Analysis of Data and Written Report:
In order to identify your unknown, you had to make some deductions about the data you gathered. It is the sequence of observations and conclusions (the analysis) that you will write about. Use the section headings below in your report. Your report should be typewritten, double-spaced, 1-inch margins, 12 pt. font, printed on one side only. Steps for identifying an unknown appear at the bottom of this page.


Write a few sentences of introduction (no flowery phrases about the importance of spectroscopy in modern chemical analysis) -- just a few simple, to-the-point sentences explaining the goal of the experiment and the general procedure.

Explain what data you amassed and how you acquired it. Since the experimental data is included in the Report Form, you do not need to repeat it here in detail -be brief. Do your analysis in the next section, not in the Data section.

You must incorporate your findings as part of your analysis. (See the section below on "Steps in Identifying an Unknown".) Your audience is a chemist who is familiar with all the procedures and wants to know where your data came from and the conclusions you drew during its analysis. (The chemist-reader does not need to know how you set up a simple distillation or how you read the refractometer.)


Steps in Identifying an Unknown

Although there is no one correct approach to identifying an unknown, the following is "tried and true". If you deviate from this method substantially, you should justify doing so in your written Analysis Section. If you have identified your unknown in some unorthodox way (e.g. by "intuition", finding it in the text, or examining every spectrum in a database, or guessing), you should include a comprehensive retro-analysis of all your data in compensation.

  • If the laboratory included qualitative analysis, the preliminary identification of functional groups will have been made at this stage. Begin your discussion with these results. You can then discuss how the IR and NMR (Chem 318) either supported or refuted your preliminary identification.

  • Examine the IR, following the steps recommended in the text or in class. Explicitly state what functional groups you think might be present and what functional groups are absent. If you have some conflicts or uncertainties, that is alright -- make a statement to that effect. This comprehensive IR analysis must be included in the Analysis section of the written report. The analysis must be consistent with the marked-up experimental IR.

  • If you have an NMR, draw conclusions about the structure by explicitly considering the chemical shifts, splitting patterns, and integration. You might or might not have tentatively identified the compound at this point. Either way, state so in your analysis report.

  • If there is a short list of unknowns to consult, eliminate all those that cannot be your unknown on the basis of the structural groups that you know are absent. Take into account the water-solubility test to further narrow the list.

  • From the narrowed list of possible unknowns, find their b.pt/ref. index in the literature. You probably will have identified the unknown at this point. (Remember, the boiling point is not as reliable a measurement as melting point. A temperature-corrected refractive index should match the literature to two decimal places.) Make sure to mention these properties in your discussion.

  • If you have tentatively identified your unknown after considering all your data, or if you have narrowed the list to a few possibilities, examine spectra databases (print or on-line) for final confirmation of identity and to obtain a copy to submit with your report. Cite the source of the spectrum directly on the spectrum.

  • If you narrowed down the possible unknowns by a property such as boiling pt. or refractive index, state what source you searched.

In your written analysis, explicitly comment on the correspondence (match or not match) between your experimental and literature IR. If they do not match and you say they do, or if you say they "resemble" or are "similar" (or you do not comment on the non-match), 50% of the written report grade will be deducted. If you say they do not match (and they do not), but you make no further effort, 50% of the written report grade will be deducted.

Assemble your report in this order:

  • Report form
  • Experimental IR; NMR (NMR for Chem 318 only);
  • Lliterature IR and NMR (NMR for Chem 318 only);
  • Qualitative analysis table and equations page (where applicable)
  • Calculations
  • Written report with a title and subheadings Introduction, Data, Analysis, and Conclusion.

Staple the complete report in the upper left corner.

You will be graded for adherence to these instructions.