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Structure determination of organic compounds by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic tech - Government Jobs PDF Download

Spectroscopy

Methods of structure determination

  • Nuclear Magnetic Resonances (NMR) Spectroscopy (Sections 13.3-13.19)
  • Infrared (IR) Spectroscopy (Sections 13.20-13.22)
  • Ultraviolet-visible (UV-Vis) Spectroscopy (Section 13.23)
  • Mass (MS) spectrometry (not really spectroscopy) (Section 13.24)

Molecular Spectroscopy: the interaction of electromagnetic radiation (light) with matter (organic compounds). This interaction gives specific structural information.

Mass Spectrometry:

Molecular weight of the sample → formula

The mass spectrometer gives the mass to charge ratio (m/z), therefore the sample (analyte) must be an ion. Mass spectrometry is a gas phase technique- the sample must
be “vaporized.”

Structure determination of organic compounds by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic tech - Government Jobs Structure determination of organic compounds by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic tech - Government Jobs

Structure determination of organic compounds by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic tech - Government Jobs

B= magnetic field strength
r = radius of the analyzer tube
V= voltage (accelerator plate)

Structure determination of organic compounds by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic tech - Government Jobs

The Mass Spectrometer

Exact Masses of Common Natural Isotopes

Isotope mass natural abundance Isotope mass natural abundance
1H 1.00782 99.985 19F 18.99840 100.00
2H 2.01410 0.015 35Cl 34.96885 75.77
12C 12.0000 98.892 37Cl 36.96590 24.23 (32.5%)
13C 13.0033 1.108 (1.11%) 79Br 78.91839 50.69
14N 14.00307 99.634 81Br 80.91642 49.31 (98%)
15N 15.00010 0.366 (0.38%) 127I 126.90447 100.00
16O 15.99491 99.763      
17O 16.99913 0.037 (0.04%)      
18O 17.99916 0.200 (0.20%)      

Molecular Ion (parent ion, M) = molecular mass of the analyte;sample minus an electron

Base peak- largest (most abundant) peak in a mass spectra; arbitrarily assigned a relative abundance of 100%.

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FAQs on Structure determination of organic compounds by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic tech - Government Jobs

1. What is the purpose of IR spectroscopy in the structure determination of organic compounds?
IR spectroscopy is used to identify the functional groups present in an organic compound. It provides information about the types of bonds and the presence of functional groups, such as alcohols, carbonyls, and amines. By analyzing the absorption peaks in the IR spectrum, chemists can determine the structure of the compound.
2. How does UV-Vis spectroscopy contribute to the structure determination of organic compounds?
UV-Vis spectroscopy helps determine the presence of conjugated systems in organic compounds. Conjugated systems absorb light in the ultraviolet and visible regions, resulting in characteristic absorption bands in the UV-Vis spectrum. By analyzing these absorption bands, chemists can infer the presence of double bonds, aromatic rings, and other conjugated systems, which aid in determining the compound's structure.
3. Why are 1H and 13C NMR spectroscopy important in the structure determination of organic compounds?
1H and 13C NMR spectroscopy provide valuable information about the connectivity and environment of hydrogen and carbon atoms in an organic compound. By analyzing the chemical shifts and coupling patterns observed in the NMR spectra, chemists can determine the number and types of hydrogen and carbon atoms present, as well as their arrangement within the molecule. This information is crucial for elucidating the compound's structure.
4. How does mass spectrometry assist in the structure determination of organic compounds?
Mass spectrometry helps determine the molecular weight and fragmentation pattern of organic compounds. It ionizes the compound, separates the ions based on their mass-to-charge ratios, and detects the resulting mass spectrum. The molecular weight obtained from the mass spectrum provides important clues about the compound's structure, while the fragmentation pattern helps identify the functional groups and connectivity of atoms within the molecule.
5. What are the advantages of using multiple spectroscopic techniques in the structure determination of organic compounds?
Using multiple spectroscopic techniques, such as IR, UV-Vis, NMR, and mass spectrometry, offers complementary information about the compound's structure. Each technique provides unique insights into different aspects of the molecule, such as functional groups, conjugation, connectivity, and molecular weight. By combining the data from these techniques, chemists can obtain a more complete picture of the compound's structure and increase the accuracy of their analysis.
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