TOPIC 7: MODERN ANALYTICAL TECHNIQUES

Question 1

List the common fragments and their molecular Masses

Answer 1

1. CH3+=15
2. C2H5+=29
3. CH3CH2CH2+=43
4. CH3CHCH3+=43
5. OH+=17

Question 2

What does the M+ ion peak tell us

Answer 2

Tells us the relative atomic mass of the compound

Question 3

What causes the presence of an M+1 peak on the mass spectra of most organic compounds

Answer 3

For most organic compounds the M peak is the one with the second highest mass/charge ratio

The smaller peak to the right of the M peak is called the M+1 peak - it is caused by the Carbon isotope 13 C

Question 4

Describe what happens in infrared spectroscopy

Answer 4

1. A beam of infrared radiation is passed through a sample of a chemical.
2. The infrared radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy
3. Bonds between different atoms absorb different frequencies of IR radiation

Question 5

What does a infrared spectrometer show us ?

Answer 5

1. It produces a graph that shows what frequencies of radiation the molecules are absorbing.
2. The peaks show you where radiation is being absorbed
3. Transmittance is always plotted on the y-axis and wavenumber on the x-axis. Wavenumber is the measure used for the frequency (it is just 1/wavelength in cm)