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Why collect NMR or MS^n data?

February 19, 2008
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs

As would-be elucidators dive into an elucidation for an organic unknown, narrowing down a single molecular formula (MF) becomes vital in simplifying the elucidation. However, one hurdle quickly leads into another. As the total atom count adds up, the number of possible isomers increases just as much (See Table and Graph below).

I can’t imagine drawing by hand every possible isomer for C12H26 at 355. And even if I did, how would I determine the candidate structure? The only choice is to acquire additional data to help eliminate the poor candidates. In my experience, the best choices are 1D and 2D NMR, MSn, and/or single-crystal XRD data.

MF                         Number of Isomers
CH4                                   1
C2H6                                 1
C3H8                                 1
C4H10                               2
C5H12                               3
C6H14                               5
C7H16                               9
C8H18                              18
C9H20                             35
C10H22                            75
C11H24                            159
C12H26                            355
C15H32                           4,347
C20H42                        366,319
C30H62               4,111,846,763
C40H82       62,491,178,805,831
C10H17Br2ClO2        50,502,293
C15H22O2          38,136,211,624
C15H20O1          37,568,150,635
C12H12O3          68,930,547,646

Graphmf

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