Box 23-1 shows the separation of enantiomers with the formula C9H4N2Cl6.
(a) Verify that the formula for rings double bonds (21-3) agrees with the structure.
(b) Find the nominal mass of C9H4N2Cl6 (Box 21-1)
(c) The high-mass region of the electron impact mass spectrum of one enantiomer is shown on page 594. Suggest an assignment for m/z 350, 315, 280, 245, and 210.
(d) The relative abundance of 35Cl and 37Cl in a molecule containing n Cl atoms is given by the terms of the binomial expansion

an-3 b3 + ..... where a is the natural abundance of 35Cl (0.757 7) and b is the natural abundance of 37Cl (0.242 3). The first term gives 35Cln1 37Cl1, and so forth. The spreadsheet below shows how to compute the terms of (a
b) 6 with Excel in cells D8:D14. In cell D8, the function is "
BINOMDIST(A8,$B$5,$B$3,FALSE)" BINOMDIST (6,6,0.7577,FALSE), which translates into D8 (0.757 7)6. When you highlight cell D8 and Fill Down, the function in cell D9 is "BINOMDIST (A9,$B$5,$B$3,FALSE)" BINOMDIST (5,6,0.7577,FALSE), which translates into D9 6(0.757 7)5 (0.2423)1-the second term of the expansion. Column E normalizes the abundances in column D so that the most intense peak is 100. The spreadsheet predicts that a molecule with 6 Cl atoms will have
a ratio of intensities M :M2:M4:M6:M8:M10 :M12
52.12 : 100 : 79.95 : 34.09 : 8.18 : 1.05 : 0.06 (if there are no other
significant isotopes of other elements in the molecule). Compute the
expected abundances of Cl isotopes for species with 5, 4, 3, and 2 Cl
atoms and compare your results with the observed clusters in the
mass spectrum.
. . . ,

Transcribed Image Text:

nin 2) 3! 2!