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    hi im stuck on using mass spectroscopy to identify halogen compounds using [M+2] and [M+4] peaks, basicaly i dont understand where do there peaks come from and how do they help us identify compounds

    Thanks alot

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    fact - chlorine has two isotopes 35-Cl and 37-Cl

    fact - the natural ratio of these two isotopes is 3:1

    any compound contianing chlorine will have peaks for molecules that contain each isotope. eg CH3Cl will have a peak at m/e = 50 and m/e = 52 corresponding to the molecules containing the 35 and 37 isotope respectively.

    If a molecule contains two chlorines eg CH2Cl2 then you would expect peaks corresponding to m/e = 84, 86 and 88 - the first having two 35-Cl isotopes, the second having one 35Cl and one 37Cl and the third containing two 37-Cl isotopes.

    see http://www.ibchem.com/IB/ibnotes/full/ato_htm/12.1.htm
 
 
 
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