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Spectroscopic Identification of Organic Compounds

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Kevin Buckley

on 22 May 2017

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Transcript of Spectroscopic Identification of Organic Compounds

Spectroscopic Identification of Organic Compounds
Table of Contents

1. IDH - Index of Hydrogen Deficiency
2. IR - Infrared Spectroscopy
3. MS - Mass Spectroscopy
4. H NMR - Proton Nuclear Magnetic Resonance Spectroscopy
5. IB Questions
6. Sources
Application and skills:
1. Determination of the IHD (Index of Hydrogen Deficiency) from a molecular formula/ structure

2. Deduction of information about the structural features of a compound from MS and IR graphs
1
Index of Hydrogen Deficiency
Degree of Unsaturation
can determine the number of rings/ multiple bonds in a molecule from a molecular formula/structure
The IHD is used to calculate the number of rings and bonds present, where:
a double bond = 1 degree
a triple bond = 2 degrees
a ring = 1 degree
an aromatic ring = 4 degrees
}
degrees of unsaturation
IHD can be worked out from:
molecular formula
structure of the molecule
IHD - Structure
Aspirin
Benzene
(Examples)
1 ring = one degree
3 double bonds = 3 x 1 degrees
IHD
= 3 +1 =
4
5 double bonds = 5 x 1 degrees
1 ring = one degree
IHD
= 5 + 1 =
6
IHD - Molecular Formula
Generic molecular formula:
C H N O X
c
h
n
o
x
IHD formula :
(0.5)(2c+2-h-x+n)
Example:
Cocaine -
C
17
H
21
NO
4
c = 17
h = 21
n = 1
o = 4
x = 0
IHD = (0.5)(2
c
+2-
h
-
x
+
n
)
IHD = (0.5)(2*
17
+2-
21
-
0
+
1
)
IHD = (0.5)(34+2-21-0+1)
IHD = (0.5)(16)
IHD = 8
Infrared Spectroscopy
IR region of the EMS - light with longer wavelength and lower frequency than visible light.
IR Spectroscopy can identify various
functional groups
in a molecule.
What is spectroscopy???
It is the study of the way matter and radiation interact.
IR Spectroscopy uses the fact that molecules absorb specific frequencies that are characteristic of their structure.
some frequencies are absorbed when IR lights is put through any sample
y-axis: transmitance (%)
x-axis: wavenumber/cm^-1
100
50
0
transmittance(%)
wavenumber/cm^-1
4000
2000
500
100% transmittance means no light was absorbed
the lower the transmittance %, the more light is absorbed>>this energy can cause a bond to stretch or "
vibrate
" - easier to identify bond type
IR Spectroscopy Example
Simplified Chart

Bond
Wavenumber
C - Cl
C - O
C = C
C = O
C = C
O - H (in carboxylic acids)
C - H
O - H (in alcohols)
600-800
1050-1410
1620-1680
1700-1750
2100-2260
2500-3000
2850-3090
3200-3600
Anyways...
Butanoic Acid
MS - Mass Spectrometry
analytical technique that helps identify the amount and type of chemicals present in a sample
measuring mass-to-charge ratio
A mass spectrum is a plot of the ion signal as a function of the ratio
the spectra are used to determine the elemental or isotopic signature of a sample, masses of molecules, etc.
MS - Mass Spectrometry
It works by ionizing chemical compounds to generate charged molecules or fragments.
A mass spectrometer consists of
3
components:
an ion source, a mass analyzer, and a detector
The ionizer
converts some of the sample into ions.
An
extraction system
removes ions from the sample, are then targeted through the
mass analyzer
and onto the
detector
.
The differences in masses of fragments allow the mass analyzer to sort the ions by their mass-to-charge ratio.
The
detector
measures:
- value of an indicator quantity
- provides data for calculating the abundances of each ion present
Analysis of MS spectra
Question time!
ZANAMIVIR
Sources
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtjml/Spectrpy/Images/masspec1.gif
https://en.wikipedia.org/wiki/Infrared_spectroscopy
the chemistry book
msjchem.com
http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Nuclear_Magnetic_Resonance/Nuclear_Magnetic_Resonance_II
http://www.chem.ucla.efu/harding/ec_tutorial78.pdf
Patty Kronert Prezi slides
NMR Spectroscopy
Proton Nuclear Magnetic Resonance
Index of Hydrogen Deficiency
The IHD for a hydrocarbon with x Carbon atoms and y Hydrogen atoms is given by the following equation:
Key idea: Area under the peaks is proportional to the ratio of Hydrogen in each environment
HL!
Why use TMS as the reference point?
High Resolution Proton NMR
Key idea: Looking on the adjacent Carbon to the one whose Hydrogen Environment we are looking at, +1 to its number of Hydrogens to get number of peaks!!!!
Putting it all together!!!
Full transcript