Question

12 electrophillic addition of bromine (1) - Word Layout References Mailings Review View Help Tell me what you want to VA A A A E EFET x x A - aty - A I E. AaBbCD AaBbCcD 1 Normal 1 No Spac... . Font Paragraph pom ppm 5. Below is the mass spectrum of stilbene dibromide. a. The molecular ion is found at 338. Why is it so small (what falls off easily)? b. What isotopic effect causes the presence of peaks at 259 and 261 c. The most abundant fragment is at 180. What fragment does this represent? Relative Intensity 0- பார்ப 150 50 ரர்பராராராராராராராராராராராராராரா 200 250 300 m/z
I just need this explained.

Answer 1

fast Br m/z=180 a) In the stilbene dibromide the C-Br bond breaks fast to give stable benzylic radical and these two radicales combine to give stilbene. Hence the molecular ion peak is very small. Br b) After breaking of one of the C-Br bond the resulting benzylic radical is very stable but it contains only one Br atom and hence due to two isotops of Br and Br there are peaks at 259 and 261. The natural abundance of these isotops is almost equal and hence the peaks corrosponding to these isotops at 259 and 261 have almost equal hight. c) The base peak is at 180 due to formaiton of stilbene as a stable product.