4.2.4

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What does infrared radiation cause covalent bonds to do?
Causes covalent bonds to vibrate more and absorb energy; a bend or stretch.
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What is the effect of atmospheric gases containing C=O, O–H and C–H bonds absorbing infrared radiation?
Gases, for example H2O, CO2 and CH4, absorb the longer-wavelength IR radiation, the vibrating bonds then re-emit this energy as radiation that increases the temperature of the atmosphere close to the Earth's surface, causing global warming.
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Can you identify alcohols, aldehydes, ketones or carboxylic acids from their absorption peaks?
Different peak rates are given in the data sheet; don't forget that there will be a peak around 3000 cm^(-1) because of the C-H bonds.
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What is he fingerprint region?
An area of an infrared spectrum below 1500 cm^(-1) that gives a characteristic pattern for different compounds.
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What practical uses are there for infrared spectroscopy?
To monitor gases causing air pollution, eg. CO and NO from car emissions, and in modern breathalysers to measure ethanol in the breath.
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How do you find molecular mass from a mass spectrum?
The molecular ion peak (M+ peak) has to be located; the molecular ion peak is the clear peak at the highest m/z value on the right-hand side of the mass spectrum; the ion M+ is the positive ion when a molecule loses an electron.
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Why does the M + 1 peak occur?
Because 1.1% of carbon is present as the carbon-13 isotope.
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What is fragmentation?
Some molecular ions break down into smaller pieces known as fragments; fragmentation breaks the molecular ion into two species - a positively charged fragment ion and a radical; any positive ions will be detected.
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Can you identify parts of structures from fragmentation peaks?
Molecules fragment in slightly different ways depending on their structures; mass spectra can therefore be used to identify molecules.
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How can you identify the structures of organic compounds from different analytical data?
Elemental analysis - use of percentage composition data to determine empirical formula; mass spectrometry - use of the molecular ion peak from a mass spectrum to determine the molecular mass.
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How can you identify the structures of organic compounds from different analytical data? (continued)
Infrared spectroscopy - use of absorption peaks from an infrared spectrum to identify bonds and functional groups present in the molecule.
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Other cards in this set

Card 2

Front

What is the effect of atmospheric gases containing C=O, O–H and C–H bonds absorbing infrared radiation?

Back

Gases, for example H2O, CO2 and CH4, absorb the longer-wavelength IR radiation, the vibrating bonds then re-emit this energy as radiation that increases the temperature of the atmosphere close to the Earth's surface, causing global warming.

Card 3

Front

Can you identify alcohols, aldehydes, ketones or carboxylic acids from their absorption peaks?

Back

Preview of the front of card 3

Card 4

Front

What is he fingerprint region?

Back

Preview of the front of card 4

Card 5

Front

What practical uses are there for infrared spectroscopy?

Back

Preview of the front of card 5
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