17.2 - Infrared Spectroscopy

Question 1

How are atoms in a molecule joined?

Answer 1

Atoms in a molecule are joined by covalent bonds, which possess energy and vibrate naturally around a central point.

Question 2

What happens when the bonds absorb IR radiation?

Answer 2

the bonds stretch and bend more.

Question 3

What type of IR radiation do bonds absorb?

Answer 3

Any bond can only absorb radiation that has the same frequency as the natural frequency of the bond.

Question 4

Why does water vapour, CO2 and methane absorb longer-wavelength IR radiation re-emitted from the Earth’s surface?

Answer 4

It has the same frequency as the natural frequency of their bonds.

Question 5

Why do organic chemists use infrared spectroscopy?

Answer 5

It is used to identify bonds and functional groups present in organic molecules.

Question 6

How does infrared spectroscopy work?

Answer 6

Beam of IR radiation in the range 200-4000 cm -1 is passed through the sample.

The molecule absorbs some of the IR frequencies
and the emerging beam of radiation is analysed to identify the frequencies that have been absorbed by the sample.

Question 7

What are the dips in an IR spectroscopy graph called?

Answer 7

Peaks

Question 8

What is the fingerprint region?

Answer 8

Below 1500 cm-1 on the spectrum.
The fingerprint contains unique peaks which can be compared to a database of spectra
to identify the particular molecule under investigation.

Question 9

What type of peak does a carboxylic acid have?

Answer 9

Broad peak

2500-3330 cm-1

Question 10

What type of peak does an alcohol have?

Answer 10

3200-3600 cm-1

Question 11

What are the applications of IR spectroscopy?

Answer 11

Used in breathalysers

Used to monitor car pollution levels