3.3.6 Organic Analysis

Question 1

Explain how mass spectrometry can be used to determine the molecular formula of a compound

Answer 1

Using the peaks in mass spectrum
Heaviest ion is likely to be the molecular ion
Smaller ones could be from molecular ions breaking into fragments

Question 2

Explain how bonds in a molecule absorb infrared radiation at characteristic wavenumbers

Answer 2

Vibrating bonds absorb infrared energy at a frequency that corresponds to the vibrational frequency of the bond.
Each trough is caused because energy is being absorbed from that particular frequency of infra-red radiation to excite bonds in the molecule to a higher state of vibration - either stretching or bending.

Question 3

Describe how ‘fingerprinting’ allows identification of a molecule by comparison of spectra

Answer 3

The pattern of absorbance peaks in the fingerprint region is unique to every molecule, meaning that the data from an unknown sample can be compared to the IR spectra of known standards in order to identify