Chapter 17 - Analytical Techniques
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What are the key features of a mass spectrum?
The molecular ion peak, M, for determination of the molecular mass of the compound. Fragment ions for determination of parts of the structure. (e.g. CH3+)
The molecular mass has the same value as the __ _____.
The molecular mass has the same value as the M peak.
In the mass spectrum of organic compounds, the M+1 peak exists because 1.1% of carbon is present as carbon-13.
In the mass spectrum of organic compounds, the M+1 peak exists because 1.1% of carbon is present as carbon-13.
What effect does infrared radiation have on covalent bonds?
Infrared radiation causes covalent bonds to absorb energy and vibrate more.
How does infrared radiation affect global warming?
IR radiation is absorbed mainly by gases containing C=O, O-H and C-H bonds and re-radiated as heat energy. Increased emissions of CO2 from fossil fuel usage increases the absorption of IR radiation and global temperature during re-radiation.
What is the fingerprint region?
The region between 400cm-1 and 1500cm-1 on an infrared spectrum which is unique to every compound.
How can an unknown sample be identified using its infrared spectrum?
The infrared spectrum can be compared to a database of known IR spectra to find a match in the fingerprint region.
State two applications of IR spectroscopy.
• Monitoring gases causing air pollution (e.g. CO and NO from car emissions). • Measuring ethanol in breath using breathalysers.
How can the exact identity of a compound be found from mass composition, mass spectrum and infrared spectrum?
• Elemental analysis to determine empirical formula from percentage composition by mass of each element in a compound. • Mass spectroscopy to identify molecular mass of a compound using the molecular ion peak and empirical formula. • Fragmentation patterns to deduce structure of molecule. • IR spectroscopy to identify bonds and therefore functional groups in molecule.