Spectroscopy questions-2008

Question 1

Pyrethrins belong to a naturally occurring group of insecticides produced by the chrysanthemum daisy. The
formula of one such compound, pyrethrin I, is C21H28O3.
The analytical technique that would not provide information that is useful in determining the structure of
pyrethrin I is
A. mass spectroscopy.
B. infrared spectroscopy.
C. atomic absorption spectroscopy.
D. nuclear magnetic resonance spectroscopy.


Question 2

A sample of a hydrocarbon for analysis is placed in a strong magnetic fi eld and irradiated with electromagnetic
radiation of radio wave frequency.
This is most likely to result in

Answer is C

Answer is D

Radio wave frequencies are used in nuclear magnetic resonance spectroscopy in which the nuclei of C or H atoms are promoted to higher energy levels (option D). Option A indicated mass spectroscopy, option B indicated IR spectroscopy, and option C indicated atomic absorption or UV-Visible spectroscopy

A. ionisation and fragmentation of molecules.
B. an increase in bond vibrations of molecules.
C. the promotion of electrons to higher energy levels.
D. a change in the energy of the nuclei of the hydrogen atoms.


Question 3

The mass spectrum of ethanol is given on the right.
What fragment must have been lost from the molecular ion to account for the high peak at m/z 45?


Click to see the spectrum.