organic analysis (3.3.6)

Question 1

what can mass spectrometry be used to do?

Answer 1

determine the molecular formula of a compound

Question 2

what is the difference between the Mr values derived from low resolution mass spectrometry and high resolution mass spectrometry?

Answer 2

the value from HRMS is given to 5 decimal places while the value from LRMS is given to the nearest whole number

Question 3

what do bonds in a molecule do?

Answer 3

absorb infrared radiation at characteristic wavenumbers (1/wavelength of light in cm)

Question 4

why do the bonds in a molecule absorb infrared radiation?

Answer 4

• the bonds are constantly vibrating (stretching and bending)
• the bonds absorb radiation with the same frequency as the bond vibration
• when a bond absorbs radiation the degree of stretching or bending increases

Question 5

how can you use infrared data to identify where a certain functional group is present on a spectra?

Answer 5

1. use the IR absorption data on the data sheet to check the wavenumber range for that functional group
2. identify where on the spectra that wavenumber range is and which peak corresponds to this (remember may be more than one peak eg. for an OH alcohol)

Question 6

what is the fingerprint region on a spectra?

Answer 6

a complex series of peaks specific to the molecule being studied

Question 7

what does fingerprinting allow?

Answer 7

identification of a molecule by comparison of spectra