INFRARED SPECTROSCOPY

Question 1

How does infrared spectroscopy work? (1)

Answer 1

when you shine a beam of infrared radiation (heat energy) through a sample, the bonds in the sample can absorb energy from the radiation and vibrate more. However any particular bond can only absorb radiation that has the same frequency as the natural frequency of the bond.

Question 2

what is the first stage of the process within a infrared spectrometer? (1)

Answer 2

1. a beam of infrared radiation containing a spread of frequencies is passed through a sample.

Question 3

what is the second stage of the process within a infrared spectrometer? (1)

Answer 3

2. the radiation that emerges is missing the frequencies that correspond to the types of bonds found in the sample.

Question 4

what is the third stage of the process within a infrared spectrometer? (1)

Answer 4

3. the instrument plots a graph of the intensity of the radiation emerging from the sample, called the transmittance, against the frequency of radiation.

Question 5

what is the fourth stage of the process within a infrared spectrometer? (1)

Answer 5

4. the frequency is expressed as a wavenumber, measured in cm-1

Question 6

IN ALCOHOLS
what is the wavenumber peak for the O-H bond? (1)

Answer 6

produces a broad peak at about between 3230 and 2550cm-1

Question 7

IN CARBOXYLIC ACIDS
What is the wavenumber peak for the O-H bond? (1)

Answer 7

a very broad O-H peak between 2500 and 3000cm-1

Question 8

what is the wavenumber peak for the C=O bond? (1)

Answer 8

produces a peak between 1680 and 1750cm-1 this is found in aldehydes, ketones and carboxylic acids.

Question 9

what is the wavenumber peak for the C-O bond? (1)

Answer 9

produces a peak between 1000-1300cm-1 this is found in alcohols and esters.

Question 10

what is the wavenumber peak for the N-H bond? (1)

Answer 10

produces a peak between 3100-3500cm-1 this is found in primary amines