1. Chem 440/540 Advanced Organic Spectroscopy Introduction What spectroscopic techniques would be useful in determining the structure of this compound? H-1 NMR C-13 NMR 2D NMR (COSY and HETCOR) Mass spec (MS) Infrared (IR) Other: Index of hydrogen deficiency (IHD)

2. H-1 NMR Spectrum

3. CDCl 3 C-13 NMR Spectrum

4. General Principles of Absorption Spectroscopy A spectroscopic transition converts a molecule from a lower to a higher energy state.  E = h = frequency of the electromagnetic radiation h = Planck’s constant = c c = speed of light  E = h = hc/

5. Types of Spectroscopy Radiation TypeE (kJ/mol)TechniqueTime (sec)  -rays, x-rays 10 5 -10 3 X-ray diffraction (nuclear transitions) 10 -18 Ultraviolet-visible10 3 –10 1 UV-vis (electronic transitions) 10 -15 –10 -14 Infrared10 1 –10 -1 IR (vibrational transitions) 10 -13 Microwaves10 -3 Electron spin resonance (ESR- rotational motion) 10 -4 –10 -8 Radiowaves10 -7 NMR (nuclear spin transitions) 10 -1 -10 -9

6. Index of Hydrogen Deficiency (IHD) The degree of unsaturation can be calculated for any organic compound containing C, H, N, O, S, or the halogens. Use three steps: 1. Using the molecular formula, replace all halogens with hydrogens. 2. Remove all oxygen and sulfur atoms. 3. For each nitrogen remove the nitrogen and one hydrogen. The molecular formula is now reduced to C n H m IHD = n - m/2 + 1

7. Calculate the IHD for each of the following molecules:  -sitosterol: C 29 H 50 O 3-iodothiophene: C 4 H 3 IS 5-iodouridine: C 9 H 11 IN 2 O 6 Chloramphenicol: C 11 H 12 Cl 2 N 2 O 5

8. Steps in Determining a Molecular Structure Determine the molecular formula (MS). Calculate the IHD. Identify the functional groups (IR, NMR, UV). Establish proton connectivities ( 1 H-NMR) Establish carbon connectivities ( 13 C-NMR). Determine the positions of functional groups on the carbon framework (IR, NMR, UV). Confirm the structure by synthesis or X-ray diffraction.