Average alkyl chain length by H-NMR

Area under methyl peak = 3 protons = 10 (in arbitrary units) 

Therefore average length of fatty alkyl chain = 4.5 

The above chemical shift assignments and integrations also allow us to determine the average ethoxylate number for this surfactant. Given that the ethoxylate peak ( c ) is at 3.7 ppm  

It can be clearly seen that the terminal methyl is used as the internal standard in both these calculations, hence the importance of determining its integral with great precision. 

Why are m and n not integers Because what we have in solution is a complex mixture of molecules, each with its own integral value of n and m, and the NMR method only gives us an unweighted average of these values. This result can be readily confirmed by HPLC or SFC analysis of the mixture, where the individual oligomers can be seen. 

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