ir spectroscopy Flashcards
What is infrared in terms of molecules ?
A pair of atoms that constantly vibrates
> infrared radiation can be absorbed by molecules causing them to vibrate more meaning their covalent bonds also vibrate
How can covalent bonds vibrate ?
They either stretch or bend
At what frequency(s) do the covalent bonds vibrate at?
Usually between 300-4000cm-1
What does the degree of vibration depend on?
The bond strength ( stronger bonds vibrate at a higher frequency)
Bond length
Mass of atoms (heavier atoms vibrate at a lower frequency)
What do green house gases do in relation to infrared radiation?
They absorb the IR that is given off by the earths surface the heat would otherwise be lost to space
What does infrared radiation do in relation to global warming?
It contributes to it as it is absorbed by greenhouse gases .
>contributes to the increasing temperature of our planet
> increasing levels of greeenhouse gases may result in further global warming
How do you make an IR spectrum?
A beam of IR is passed through the sample
{this beam will have a frequency in the infrared region of the EM spectrum}
Molecules of the sample will absorb some of the frequencies
The beam that passes through Is analysed
We can plot a graph of transmittance against frequency
We can analyse the spectra formed
{the peaks in the spectrum represent the vibration caused by the abundance of the IR radiation by a specific bond in the molecule
What is the similarities/difference of the IR of ethanoic acid and ethanol?
Carboxylic acid (C=O) -> peak at 1700-1725 sharp peak caused by the C=O, par at 2500-3300 very broad peak caused by O-H
Alcohol-> peak at 3200-3750 , broad peak caused by O-H
What is the applications of IR spectroscopy ?
Breathalysers
> IR spectroscopy can be used to identify the -OH functional group that is indicative of alcohol.
> the level of absorption that is observed on the spectrum is related to the concentration of alcohol in the blood . ( UK/Wales: 80mg/100ml)
Air quality
> IR spectroscopy can be used to monitor the levels of pollutants (CO,NO)
Forensics
> IR spectroscopy can be used to identify the chemicals that are present at crime scenes
-fuels,accelerants,plastics etc
What is the finger print region?
This is the region between 500cm-1 to 1500 cm-1
The absorptions within this range is interesting as they are mainly caused from bending . Together they are largely unique to the specific molecule like a fingerprint. This region can be used to identify chemicals s
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