Chem 440/540 Advanced Organic Spectroscopy
Introduction
What spectroscopic techniques
would be useful in determining
the structure of this compound?
H
H
OH
H
HO
• H-1 NMR
• C-13 NMR
• 2D NMR (COSY and HETCOR)
H
Betulin
• Mass spec (MS)
• Infrared (IR)
Other: Index of hydrogen deficiency
(IHD)
H-1 NMR Spectrum
H
H
OH
H
HO
4.8
4.6
4.4
4.2
H
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
C-13 NMR Spectrum
CDCl3
H
H
OH
H
HO
170
160
H
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
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
E2
Energy
E = E2 - E 1
E1
 = c
c = speed of light
E = h = hc/
Types of Spectroscopy
Radiation Type
E (kJ/mol)
Technique
Time (sec)
-rays, x-rays
105-103
X-ray diffraction
(nuclear transitions)
10-18
Ultraviolet-visible
103–101
UV-vis
(electronic transitions)
10-15–10-14
Infrared
101–10-1
IR
(vibrational transitions)
10-13
Microwaves
10-3
Electron spin resonance
(ESR- rotational motion)
10-4–10-8
Radiowaves
10-7
NMR (nuclear spin
transitions)
10-1-10-9
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 CnHm
IHD = n - m/2 + 1
Calculate the IHD for each of the following molecules:

-sitosterol: C29H50O

3-iodothiophene: C4H3IS

5-iodouridine: C9H11IN2O6

Chloramphenicol: C11H12Cl2N2O5
Steps in Determining a Molecular Structure







Determine the molecular formula (MS).
Calculate the IHD.
Identify the functional groups (IR, NMR, UV).
Establish proton connectivities (1H-NMR)
Establish carbon connectivities (13C-NMR).
Determine the positions of functional groups on
the carbon framework (IR, NMR, UV).
Confirm the structure by synthesis or X-ray
diffraction.