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# The Ultimate NMR Software for Structure Characterization

1. We first need analyze what the information the mass spectroscopy is telling us.  The first  m/z value is the M peak, which tells us how many nitrogen atoms are present in the  molecular formula.  If the m/z value is even, then there are zero or an even amount of  nitrogen atoms.  If the m/z value is odd, then there are an odd amount of nitrogen atoms. In this example, the M peak has an intensity of 154.  This is an even number, so there  are 0 or an even amount of nitrogens in the structure. The second value is the M+1 peak, which tells us how many carbons are present in the  structure.  How you find this is by dividing the relative abundance of the M+1 peak by 1.1%.   MAKE SURE YOU DO NOT DIVIDE BY 1%; THIS WILL NOT GIVE YOU THE RIGHT ANSWER.   In this example, the M+1 peak relative abundance is 11.23%.  You divide this by 1.1%  and you get 10.209%.  This means that the structure has either 10 or 11 carbons. The third value is the M+2 peak, which tells us how many (if any) bromine, chlorine, or  sulfur atoms are present within the structure.  If the relative abundance is approximately  4%, then sulfur is present.  If the relative abundance is approximately 33%, then chlorine is  present.  If the relative abundance is approximately 100%, then bromine is present. In this example, the M+2 peak relative abundance is 0.26%.  This does not correspond to  any of the above stated elements, and is too small to be sulfur, so there is no chlorine,  bromine or sulfur atoms present in this molecule. We can now use this information to find a molecular formula for this structure. C10 Possibility 154 – (12 amu per C x 10C) = 34 amu left for hydrogen, nitrogen and oxygen In this case, we can rule out C10H6N2 because the IR spectrum shows that there is a carbonyl  in Zone 4, thus revealing an oxygen in the formula.  C10H6N2 lacks an oxygen.  You can also  rule out C10H202 because it does not correspond with the integrals given in the 1 H‐NMR.   The integral equals 9 (2+1+6), and H2 is not a proportionate ratio.  That leaves us with  C10H180 as our formula.