Question

The low‐resolution mass spectrum and m/z data obtained for an unknown compound seized during
the raid on a clandestine laboratory are provided. Ignore the signals below m/z 70 and the small
clusters of signals at about m/z 85 and 93. The significant signals (m/z) and their signal intensities
(%I) from the mass spectrum are: (72,2), (73,5), (74,16), (75,35), (76,8), (77,5), (78,1), (111,51),
(112,6), (113,17), (114,2), (139,100), (140,9), (141,31), (142,3), (155,50), (156,5), (157,16), (158,2).

Subsequent analysis of the same compound using a high‐resolution mass spectrometer indicated the
strongest signal in the molecular ion group of signals was at m/z 155.01376. Additional forensic
analysis by other instrumental characterisation techniques such as 1H & 13C NMR and infrared
spectroscopy (refer to a following page) provided more information about the identity of the
compound.

Figure 1. Low-resolution mass spectrum of unknown compound 100 80 60 40 20 100 25 50 75 125 m/z 150 175

1. Assign a formula and structure, and briefly comment on the likely origin of the
significant signals at m/z 75, 77, 111, 113, 139, 140, 141, 155, 156, 157 and 158 in the lowresolution
mass spectrum.

2. Name and draw the chemical structure of the compound.

Answer 1

Due to presence of chlorine atom it is available in earth crust in the forms of C 169 and C171 so that is structural composition it shows M, M + 2 peaks in mass spectra in different intensity ratios In the same way the presence of nitrogen atom it is available in nature as N 14 (major) & N 15. Therefore in mass way the spectra of nitrogen containing compounds show M and M + 2 in different intensity ratios accordingly Remaining elements also contributing to M + 1 and M + 2 peaks but with low % \r\n The molecular ion peak m/z value is odd,so that according to nitrogen rule is should have odd number of nitrogen atoms Its is showing M and M + 2 peaks in the ratio 1: 3 (approximately) therefore it should have one chlorine atom in its composition In ^1H NMR spectra aromatic region it is showing two environments with equal coupling constants