organic spectroscopy

1. CHEMY 323, (2023-24)
Timetable (MW, 08:00-09:15 am)
Section; -----
Building; S41-0031
Instructor; Dr Javed Iqbal
Office; S41-1035
Mobile; 34432280
E. mail; Jiqbal@uob.edu.bh

2. Introduction to Spectroscopy
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3.  What is Spectroscopy?
 Measurement of the amount of radiations absorbed by a substance at various
wavelengths is called spectroscopy.
OR
 Spectroscopy is the study of interaction of electromagnetic radiations with
matter and measurement of absorption of radiations of various frequencies
upon interaction with the matter.
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4.  Wavelength, λ: Distance between two adjacent crests and troughs of the wave
in the beam of electromagnetic radiations.
 Units; angstrom, nanometer, micrometer and meter.
 Frequency, v: Number of waves passing a fixed point on the path of a beam of
radiation per unit time.
 Units; Hertz (Hz) or cycle per second.
 Wavenumber, ῡ: Number of waves per centimeter. Its unit is cm-1.
 Energy, E: Every photon of specific radiation possesses exactly the same
amount of energy which is, however different from the energy possessed by the
photon of different radiations. The unit of energy commonly used is Joule.
 Parameters to characterize Electromagnetic radiations:
 Electromagnetic Radiation:
 From of energy: commonly known as radiant energy.
 Ordinary light: more visible form of radiant energy.
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5. Electromagnetic Spectrum:
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7.  Relation between Energy, frequency, wavelength and
wavenumber.
E = hv = hc/λ = hcῡ
E = Energy
h = planks constant
v = frequency
c = velocity of radiations
λ = wavelength
ῡ = wavenumber
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8. Spectroscopic techniques
Techniques Underlying principle Information obtained
UV (200-400
nm)
VIS (400-800
nm)
Quantized absorption of UV/VIS
radiations leading to electronic
excitations.
Presence and nature of unsaturation,
particularly conjugation.
IR (2.5-16 µm or
4000-625 cm-1)
Quantized absorption of IR
radiations leading to vibrational
excitations.
Presence and environment of
functional groups, especially those
containing X-H type bonds such a C-
H, O-H and N-H or multiple bonds.
NMR
(60-6000 MHz)
Quantized absorption of radio
waves leading to transitions
between different spin orientations
of nuclei in the magnetic field.
Environment of magnetically active
nuclei, such as 1H, 13C etc., and
number of nuclei of each type.
MS (~70 eV ) Determination of mass-to-charge
ratio and relative abundance of the
ions formed on electronic
bombardment of molecules.
Molecular weight, molecular formula,
molecular structure and isotopic
abundance.
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10. Elemental Analyzer
Carbon Hydrogen & Nitrogen Analyzer can be used to
determine the carbon, hydrogen and nitrogen content in
coal, coke, food, soil, fertilizer, etcin the fields of power
plant, coal mine, metallurgy, steel factory and so on.

11. Mass spectrometry
Mass spectrometry (MS) is the study of ions created as a result of ionization/fragmentation as determined
electrically in the gas phase (neutral molecules are not observed)
Mass spectrometer

12. UV Spectrophotometer
 UV-visible spectrophotometer uses light over the ultraviolet range (185 - 400 nm) and visible range (400 -
700 nm) of electromagnetic radiation spectrum.

13. IR Spectrophotometer
 IR spectrophotometer: uses light over the infrared range (700 - 15000 nm) of electromagnetic radiation
spectrum.

14. NMR Spectroscopy
 Nuclear magnetic resonance (NMR) spectroscopy is the study of molecules by recording the interaction of
radiofrequency (Rf) electromagnetic radiations with the nuclei of molecules placed in a strong magnetic field.
NMR machine

15. 15  Instrumentation:
Detector
 Although different instruments are used for measuring absorbance in different
spectral regions, in their simplest form they all consist of five main
components: (1) source of electromagnetic radiations, (2) monochromator, (3)
sample cell, (4) a detector and (5) readout device.

16. Elemental analysis
 Elemental Analysis is a process where a sample of some material (e.g., soil, waste, minerals, chemical
compounds) is analyzed for its elemental and sometimes isotopic composition.
 Elemental Analyzers are used to determine the elemental or isotopic composition of a test sample.
 An elemental analyzer can determine what elements are present, known as qualitative analysis, or how much
of each element is present in a sample, known as quantitative analysis.
 The most popular type of elemental analysis - CHNS analysis - involves burning the sample, followed by the
collection of the individual products of that combustion.
 The products are then weighed to determine composition by mass. Instead of using mass, some elemental
analyzers use spectroscopy to determine composition.
The purpose of elemental analysis is to determine the quantity of a particular element within a molecule or
material. Elemental analysis can be subdivided in two ways:
•Qualitative: determining what elements are present or the presence of a particular element.
•Quantitative: determining how much of a particular or each element is present.

17. The classical procedure for determining the molecular formula of a substance involves three steps:
1. A qualitative elemental analysis to find out what types of atoms are present . . . C, H, N,
O, S, Cl, and so on.
2. A quantitative elemental analysis (or microanalysis) to find out the relative numbers (percentages) of
each distinct type of atom in the molecule.
3. A molecular mass (or molecular weight) determination
The first two steps establish an empirical formula for the compound. When the results of the third procedure
are known, a molecular formula is found.
Elemental Analysis and Calculations

18.  All organic compounds contain carbon and hydrogen.
 In most cases, it is not necessary to determine whether these elements are present in a sample: their
presence is assumed.
 However, if it should be necessary to demonstrate that either carbon or hydrogen is present in a compound,
that substance may be burned in the presence of excess oxygen.
 If the combustion produces carbon dioxide, carbon must be present; if combustion produces water,
hydrogen atoms must be present.
 Today, the carbon dioxide and water can be detected by gas chromatographic methods.
 Sulfur atoms are converted to sulfur dioxide;
 nitrogen atoms are often chemically reduced to nitrogen gas following their combustion to nitrogen oxides.
 Oxygen can be detected by the ignition of the compound in an atmosphere of hydrogen gas; the product is
water.
 Currently, all such analyses are performed by gas chromatography, a method that can also determine the
relative amounts of each of these gases.
 If the amount of the original sample is known, it can be entered, and the computer can calculate the