isotopic isotope combinations peaks represented calculation M
35C170Br
(0.754X 0.5057)
M+2
35C18'8r
(0.754 X 0.4943)
% of M
0.381
100
0.497
130
0.122
32
+(0.246 X 0.5057) (0.246 X
+3'Cl'9Br s'CI"Br
M+ 4
relative probability of occurrence of peaks
n asam
-
Calculations involvine more haloeen atoms become lenethv - . and very tedious. A pocket programmable calculator can be used to display the relative heights of the M, M 2, M 4, etc., isotopic peaks (Figure 9). The probability of obtaining a combination of mass (M 22) where M is the combination containing only 35Cl and 79Br isotopes is given (22) by
+
+
+
C,-,"
PM+zz= i
X
C L mX on-"+' X bx-I
X em-' X d'
=o
A calculator with a peripheral printer with an automatic plotting capability, such as the Hewlett-Packard HP-41C, enables the relative heights of the isotopic peaks of a molecule containing any combination of bromine and chlorine atoms to be printed directly (Figure 9). Thus the student can immediately identify the number of bromine and chlorine atoms in a molecule by inspection of its mass spectrum. Despite the predominance of the M , M + 2, M 4, etc., isotopic peaks in the spectra of bromo- and chloro-organic compounds the (M 1)lM ratio is not affected by the presence of either chlorine or bromine and this ratio may still be used to indicate the C, H, N and 0 composition of the remainder of the molecule. The M 1oeak is related to the number of '3C, 2H, i 6 and ~ ' 7 0 isotopes in the molecule, esoeciallv those of 13C.A Docket ~roerammablecalcUht0r has been useb to display the approxhatk percentage (M + l)/M,
+
Table 1.
+
data from mass spectrum isotopic peak abundance M (235) M+ 1 M+2
abundance percentage of M
calculator display 100%
M+3
31.5
M+4 M+ 5
110.0
100.0 7.0 130.0 9.2 32.1
7.8
2.3
345.0 24.0
450.0
lor BrCl
130% 32%
cab~lalorentry: CHNO fragment mass: 121 (M- 114) NN-: 3 Nhalwenr: 2
.r C1,
+
NH < 2 NC + NN+ 2 - NmWena N~
