1. Identification of Organic Compounds. - Separation of pure samples. - Structure
assignment using analytical methods. Analytical techniques: 1.
Identification of Organic Compounds - Separation of pure samples - Structure assignment using analytical methods
Analytical techniques: 1.
Mass spectrometry
(MS)
2.
Infrared spectroscopy
(IR)
3.
Ultraviolet/Visible spectroscopy
(UV/Vis)
4.
Nuclear Magnetic Resonance
(NMR)
1
Mass Spectrometry 1.
Molecular ion (M+ ) gives molecular mass
2.
Fragmentation pattern gives information about structure
3.
M+ +1 peak gives the number of carbons
4.
Precise molecular weight allows for distinguishing between molecular compositions: (C5H12 = 72.0939
C4H8O = 72.0575)
2
Spectroscopy Electromagnetic wave
Energy of photon
E = hn
h = Planck’s constant 6.62 x 10-34 J s
(or 1.58 x 10-34 cal s)
n = c/l = frequency (in hertz) (Hertz = 1/s) l = wavelength (in m) c = speed of light (3.0 x 1010 cm/s) n = 1/l = wave number
3
Infrared Spectroscopy wavenumber (cm-1) 4000
2500
N H
2000
C C C N
O H C H 2.5
4
1500
600
C O C C
C O C C
C N
C N
5
Fingerprint region
7
16
wavelength (mm)
Frequency depends on the mass of atoms and the strength of the bond (like a spring with weights) light atoms
high frequency
multiple bonds
high frequency
4
13
C NMR Spectroscopy - Simplified Degree of Unsaturation (DU)
DU = carbons -
Code:
(4o) C
(hydrogens + halogens) 2
(2o) (3o) CH2 CH
+
nitrogens 2
(1o ) CH3
Filter (DEPT 135)
Filter (DEPT 90) LOW
FIELD
5
HIGH
+1
Nuclear Magnetic Resonance (NMR) 1
H or 13C
(19F, 31P, 2H, 15N ....)
1. Chemical shift - electronic environment 2. Integration - relative amounts of different H’s or C’s 3. Number of lines - number of different H’s or C’s (excluding coupling) 4. Coupling patterns - nearest neighbor (other nuclei with spins) 1
