Question

4) Both methylbenzene (toluene) and 1,6-heptadiyne have molecular formulas of C7Hz and molecular masses of 92. Which of the two mass spectra shown below corresponds to which compound? Explain your reasoning [6 marks] 607 MS 100 MS Relative abundance 40 80 100 100 0 ТТТТТТТТ 20 40 60 80 m/z. 100 m/z

Answer 1

Let us study the fragmentation of toluene as below-

• In the case of toluene, the two fragments at
  m/z = 92
  (Molecular ion peak) and
  m/2 = 91
  (base peak) are of intensity 75 and 100 respectively. This means in the case of toluene, two peaks of intensities 75 and 100 are beside one another. In spectra A only, you can observe such TWO peaks beside one another one at m/z 91 (100) and to its right the peak with m/z = 92 (75). Hence, spectra A corresponds to TOLUENE and spectra B corresponds to 1,6-heptadiyne.
• 
  4) Both methylbenzene (toluene) and 1,6-heptadiyne have molecular formulas of C7Hz and molecular masses of 92. Which of the two mass spectra shown below corresponds to which compound? Explain your reasoning [6 marks] 10 TMS 100 7 MS Toluene 1,6-heptadiyne Relative abundance TTTTTTTT 40 ' 60 80 100 0 ТТТТТТТТ 20 40 60 80 m/z. 100 m/z
  

The complete fragmentation of toluene is given below-

molecular ion peak | 1 Base Peak fragment ॥ 4 m|x = ੧੨ . ragment + m/7 –੧ most stable : unaitable / - ਅ - ਅਦ = 11 unstable E) m/ = 5।