lab 1(2) - Characterization of Organic Solids and Liquids...

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Characterization of Organic Solids and Liquids by Elemental Analysis, Mass Spectrometry, Melting Point, Boiling Point and Infrared Spectroscopy Mayank Kumar February 9, 2007 Methods and Background The purpose of the experiment was to determine the structures of an unknown organic solid and liquid using the analytical techniques of elemental analysis, mass spectrometry, melting point (for the solid) and boiling point (for the liquid) determination and infrared spectroscopy. Elemental analysis is used to determine the empirical formula of a compound by comparing the relative abundances of the elements which comprise the compound. The relative abundances of the elements are assumed to be masses (% → g); thus the molecular mass of the compound (hypothetically) becomes 100 g, which allows for conversion of the relative elemental abundances into molar quantities that can be compared to yield ratios of the elements in the compound. Mass spectrometry is used to determine the mass-to-charge ratio ( m/z ) of ions. Mass spectrometers ionize samples by hitting them with high-energy electrons as well as through irradiation and chemical techniques. The ions are then sorted according to their m/z ratio by a magnetic field in the mass analyzer. Mass spectra display the intensity of ion signals versus the m/z . The molecular ion peak provides the mass of the compound. Source: http://www.asms.org/whatisms/p5.html
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Given the molecular mass of a compound through mass spectrometry, the molecular formula can be determined. The molecular mass of the compound is compared to the molecular mass calculated from the empirical formula to provide a multiplication factor, which is applied to the empirical formula to yield the molecular formula. The index of hydrogen deficiency (IHD) is used to determine the total number of double bonds, triple bonds, and rings in a compound by comparing the number of hydrogens present in the compound were it saturated with the actual number of hydrogens present in the compound; there can be any combination of the aforementioned functional groups and attributes contributing to the IHD. Infrared (IR) spectroscopy is used to determine the presence of functional groups in compounds by the characteristic transmittance of IR light through the compound. The transmittance is unique to different functional groups because of specific stretching vibrations of atomic bonds attained at certain energy levels (corresponding to particular wavelengths of light). IR spectra display the percent transmittance of IR light versus the wavenumber (10,000/λ), and peaks correspond to particular functional groups. Source: http://orgchem.colorado.edu/hndbksupport/irtutor/tutorial.html Melting point and boiling point determination are used to choose the true structures (from the possible structures) of unknown solids and liquids, respectively, as these properties are physical constants.
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lab 1(2) - Characterization of Organic Solids and Liquids...

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