Question

How can you distinguish M and M+2 values for 2-chloropropane and 2-bromoprpane in Mass spectra

Answer 1

In mass spectrum the molecular ion peaks are represented by M,M +1,M+2 etc., where

M is the base peak of the compound with more abundance and greater intensity and remaining all peaks are less abundance and less intense than the base peak.

coming to the 2-chloropropane compound whose molecular formula is as CH₃(CH)ClCH₃ the base peak we observe at mol.wt(m/z) 78 by taking C¹² H¹ Cl³⁵ but for the same compound M+2 peak is observed at mol.wt(m/z) 80 by taking C¹² H¹Cl³⁷ here the peak heights are in 3:1 ratio which represents the Cl³⁵ is 3 times much than the Cl³⁷ isotope.

similarly for the second compound 2-bromopropane the M and M+2 peaks are observed at m/z 122 and 124 respectively by taking C¹²H¹Br⁷⁹ and C¹² H¹ Br⁸¹ but in this compound the heights of peaks ratio is 1;1 ratio which represents the bromine isotopes are exist in 1:1 ratio in the nature..