Unknown 1 Report: Spectroscopic Identification of an Unknown

Formula Analysis

1. According to your mass spectrum, does your unknown contain bromine? Chlorine? Answer briefly but specifically how you know for each element, using only the most-reliable/guaranteed indicator of each as discussed in class (e.g., do not assume a C–X bond will fragment if it is present). [1 pt]

2. Calculate the empirical formula, using only your elemental analysis. If you have a halogen (element “X”), you may also use your previous answer regarding which halogen it is. [1 pt]

3. Determine the molecular formula. Briefly explain how you arrived at your answer, specifically mentioning any relevant spectral data and other numerical analysis. [1 pt]

 
4. Using the molecular formula, calculate the mass its molecular ion would be expected to have on the mass spectrum. Pay close attention to units and precision as appropriate for MS mass calculations. [1 pt]

5. Based on your molecular formula, calculate the degrees of unsaturation (index of hydrogen deficiency) that the compound has. [1 pt]

MS Analysis

Write all answers for these questions directly on the MS page. Be sure it is clear which one specific signal on the graph or entry in the data table each answer refers to (the grader will not guess when there are several signals in close proximity to an answer).

6. Find the molecular ion signal. Clearly label it “M+”. Draw the structure of the ion corresponding to it. Remember to include the net charge for the structure; you do not need to label a formal charge on any specific atom. [1 1/2 pt]

7. Find the base peak signal. Clearly label it “base peak”. Write the molecular formula (with correct isotopic notation and net charge) corresponding to it. Remember that a molecular formula does not contain any structural detail. [1 1/2 pt]

8. Pick any one other signal (not M+ or base-peak) corresponding to a fragment ion. Clearly label it “fragment”. Draw the structure of the ion corresponding to it (this is a substructure or portion of your compound’s whole structure). Remember to include formal charge on the specific atom(s) rather than a net charge. [1 pt]

 
IR Analysis

9. On your IR graph, label all the relevant signals using the three-part labeling scheme (“functional group; specific bond or substitution pattern; stretch vs bend motion”; for example “alkyl; sp3 C-H; stretch” or “aromatic; 1,3,5-trisubstitution; bend”). Double-check that your analysis here is specific to and consistent with your proposed structure and completely supports all details of the structure to the extent visible on the graph. [4 pts]

1H-NMR Analysis

10. Complete the following table, tabulating the information from the 1H-NMR spectrum. List the chemical shift of each signal, along with the actual number of hydrogen atoms the signal represents in the structure and the name of its splitting pattern. Remember that a chemical shift is a single number (middle of the splitting pattern) as best you can estimate it from the graph, not a range. For the splitting patterns, you are welcome to use their appearance as best the given graph can be read in cases of undecipherable multiplets (don’t worry if it’s imperfect compared to the structure itself). Add rows to this table as necessary. [3 pts]

Chemical shift
δ (ppm) Integration
(# H in structure) Splitting Pattern

11. On your graph page, draw the structure with all hydrogens clearly labeled HA/HB/etc. according to which ones are equivalent. Double-check that you have explicitly included the correct number of hydrogen atoms on each carbon. [2 pts]

12. Place HA/HB/etc. labels on the graph signals to match them to your labeled structure. Remember that every H in the structure must be represented on the graph. [2 pts]

 
13C-NMR Analysis

13. On your graph page, draw the structure with all carbons clearly labeled CA/CB/etc. according to which ones are equivalent. [2 pts]

14. Place CA/CB/etc. labels on the graph signals to match them to your labeled structure. Remember that every C in the structure must be represented on the graph. There might be cases where you cannot make a definitive match, so it’s okay to label a pair of signals together as corresponding to two different C when there is not enough information to determine exactly which is which. [2 pts]

Summary

15. Write the serial-number of your unknown (the full “Q2P...” identifier):

16. Identity of compound. Draw the structure of your unknown (any implicit/explicit style from our course is okay). [4 pts]

17. Complete the following chart with the number of carbon atoms in your structure for each description. [2 pts]

Description: sp sp2 sp3
non-chiral sp3
chiral
#C: