Alkyl Halides and the M 2 Peak

Most of the elements found in organic compounds, such as carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, fluorine, and iodine, have one major isotope. Chlorine and bromine, on the other hand, have two, giving characteristic patterns to the mass spectra of their compounds. 

Chlorine has two common isotopes, and Cl, which occur naturally in a 3 1 ratio. Thus, there are two peaks in a 3 1 ratio for the molecular ion of an alkyl chloride. The larger peak— the M peak—corresponds to the compound containing Cl, and the smaller peak—the M + 2 peak—corresponds to the compound containing Cl. 

What molecular Ions will be present in a mass spectmm of 2-chloropropane, (CH3)2CHCI  

Calculate the molecular weight using each of the common isotopes of Cl. 

S3mpl6 Probl6m 13.2 Propose possible molecular formulas for a compound with a molecular ion at m/z = 86. 

Because the molecular ion has an even mass, the compound likely contains C, H, and possibly O atoms. Begin by determining the molecular formula for a hydrocarbon having a molecular ion at 86. Then, because the mass of an O atom is 16 (the mass of CH4), replace CH4 by O to give a molecular formula containing one O atom. Repeat this last step to give possible molecular formulas for compounds with two or more O atoms. 

Problem 13.2 Propose two molecular formulas for each of the following molecular ions (a) 72, (b) 100 (c) 73. 

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Fig. 5.32. Alkylation and GC of aqueous inorganic halides. A, authentic salts B, solution prepared on a cation-exchange column. Peaks 1 = methylfluoride 2 = water 3 = methyl chloride 4 = methyl bromide 5 = trimethylamine 6 = methyl iodide. Conditions stainless-steel column, 10 ft. x 1/4 in. O.D., Chromosorb 101 (80-100 mesh) helium flow-rate, 75 ml/min column temperature, 125°C injection port temperature, 360°C 6 til of an aqueous solution of tetramethylammonium halides (0.25 M each) injected. (Reproduced from Anal. Chem., 42 (1970) 1672, by courtesy of J. MacGee and the American Chemical Society.)...

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