Experiment 14:

1. Experiment 14: IR AND NMR IDENTIFICATION OF AN UNKNOWN

2. Objectives: • To learn how to interpret IR and NMR spectra. • To use IR and NMR spectra to propose a structure for an unknown, given the molecular formula.

3. Before coming to lab… • Go to the website: www.ochem.com • From the left menu, select TUTORIALS. • From the right column, PRELECTURES, scroll ¾ of the way down the page. • Watch the following: • SPECTROSCOPY (Part 3 of 4) • SPECTROSCOPY (Part 4 of 4) (YOU’LL BE GLAD YOU DID! )

4. IR SPECTROSCOPY • THINGS TO CONSIDER… • What kinds of bonds do I have? • If they appeared in the IR spectrum, where would they be? • Now, look at the spectrum. Are they there?

5. IR SPECTROSCOPY

6. IR SPECTROSCOPY Full IR Absorption Correlation Table in Appendix J

7. CALCULATING DEGREE OF UNSATURATION CcHhNnOoXx DU = (2c + 2) – (h – n + x) 2 • 1o unsaturation = 1 C=C or 1 ring • 2o unsaturation = 2 C=C, 2 rings, or CΞC, or combination of C=C & rings • 3o unsaturation = combination of double bonds, triple bonds, rings • 4o unsaturation = typically indicates an aromatic ring

8. 13C-NMR SPECTROSCOPY • Information provided: • Functionality (Chemical Shift) • tells the type of carbon • via position of signal on x-axis • Presence of symmetry • via # of signals • Presence of non-protonated carbons • via small signals • sometimes useful, not always!

9. TYPICAL CHEMICAL SHIFTS • 190-220d • aldehydes, ketones • 160-190d • esters, amides, carboxylic acids, acyl halides • 110-160d • arenes, alkenes • 50-110d • alkynes, sp3C attached to functional groups • 0-50d • sp3C-Csp3, where 4o>3o>2o>1o

10. 13C NMR CHEMICAL SHIFT CORRELATION CHART p. 118 in lab manual

11. 1H-NMR SPECTROSCOPY Information provided: A. Functionality • chemical shift • tells the type of hydrogen • Via position on x-axis B. Presence of symmetry • via the # signals C. Number of protons of each type per signal • Integration D. Number of neighboring protons per signal • via the splitting patterns • n+1 rule, where n=# of protons on neighboring carbons

12. TYPICAL CHEMICAL SHIFTS • 10-12d • carboxylic acid • 9-10d • aldehyde • 6.5-8.5d • aromatic • 5.0-6.5d • alkene • 2.0-4.5d • alkyne, hydrogens on carbons attached to functional groups • 0-2.0d • sp3C-H, typically 3o>2o>1o

13. 1H NMR CHEMICAL SHIFT CORRELATION CHART

14. SYMMETRY & EQUIVALENCE • Notice that there are 8H according to the MF, but we only see 3 signals. • This is because some of the hydrogens are equivalent. • Number of signals = number of different types of hydrogens present • There are 3 different signals because the hydrogens are in 3 different environments. C4H8O2

15. INTEGRATION • The integration is proportional to the # hydrogens causing that signal. • There are 3 Ha protons • There are 2 Hb protons • There are 3 Hc protons 2H 3H 3H C4H8O2

16. SPLITTING s • Splitting of a signal occurs b/c the chemical shift of a signal can be affected by neighboring protons. • Splitting = n + 1, where n = # neighboring protons. Must be within 3 bonds or less. • Equivalent hydrogens DO NOT split each other, so Ha would not split each other. • Protons cannot “see” through atoms such as oxygens or nitrogens. t q n=3, so n+1 = 4 (quartet) n=0, so n+1 = 1 (singlet) n=2, so n+1 = 3 (triplet)

17. TABLE 14.1

18. COMBINED SPECTRAL PROBLEMS • Once you have completed Table 14.1, you will notice 3 questions, followed by 3 sets of combined spectral problems. • Each page contains a 1H NMR spectrum, a 13C NMR spectrum, and an IR spectrum pertaining to one of the compounds in Table 14.1. • You must identify which set of spectra belong to which compound, and complete the tables by recording actual chemical shift values and IR absorptions.

19. EXAMPLE TABLE H3 C1 C5 H4,5 C2 H6 C6 C3 C4 Enter ACTUAL IR frequencies from spectra…NOT base values! Enter ACTUAL NMR chemical shifts from spectra…NOT base values! Do not include integration or multiplicity!

20. PROPOSING A STRUCTURE • The final part of the experiment is to practice the ability to propose a structure, given only the molecular formula (MF) and a set of IR and NMR spectra. • The best place to start is to calculate the degree of unsaturation using the provided MF, and use this information as a starting point in the proposal of possible structures.

21. PROPOSING A STRUCTURE • Using the MF, calculate the degrees of unsaturation. • Propose possible structures based on the MF and information gathered from the degrees of unsaturation. • Identify how many signals would appear in the spectra of each of the possible proposed structures based on symmetry and equivalent protons. • Identify approximate chemical shifts where these types of carbons/protons would appear based on correlation tables. • Identify splitting patterns of each type of proton present in each of your proposed structures. • Observe the spectra. Using the information you have, eliminate possible structures until you have identified the actual structure.

22. For next lab… • The FINAL LAB REPORT for Experiment 14 will be due at the beginning of class! • The PRE-LAB notebook entry for Experiment 15 will be due at the beginning of class! • Safety goggles and closed toe shoes are MANDATORY!