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Maximize Data Extraction (MDE) from a 1H NMR Spectrum

April 9, 2008

Here is a lesson I learnt over time while working on small molecules—my Elucidation Evolution.

Thinking back to when I started doing elucidations of unknowns, my mindset was to collect loads of data (NMR, MS, IR, etc.) whether I needed it or not. Initially inexperienced, I was extracting bits and pieces of information from various datasets and building up a list of fragments that needed to be combined together to form a candidate structure. Although this offered a means to practice and learn how to interpret a wide array of data, it was not an efficient approach to an elucidation.

Please note that there is value in collecting additional data to confirm or verify a candidate structure. However, for elucidation purposes, one should maximize data extraction while minimizing data collection.

As my skills grew, I felt more comfortable working with less data. I began to maximize the information I could extract from a simple 1H NMR, thus avoiding the need to collect and analyze “duplicate data”. (An example of duplicate data is a 1H NMR and a 1H-1H COSY.) Although 1H-1H COSY data could be valuable in cases with complicated resonances and a high degree of signal overlap, a 1H NMR could suffice in extracting structural information.

For the purpose of an elucidation, one should extract the following bits of information from a 1H NMR spectrum:

presence of proton resonances,

spectrum purity (identifying impurities or mixtures),

identifying aromatic and/or aliphatic protons,

presence of exchangeable protons,

chemical shifts,

proton count from integrals,

presence of symmetry,

coupling patterns and constants,

second-order effects.

TIP: Every bit of information helps. A negative result is also telling you something.

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