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ACD/Labs Blog

Arvin Moser
One of the trickiest parts of interpreting NMR data is identifying what signal belongs to the unknown compound and what can be classified as an impurity. In this case, impurities are described as extra signals coming from a solvent(s), a side product(s), extraction/purification process, etc. The 1H NMR spectrum below is for an unknown compound....

Arvin Moser
A deuterated solvent can impact whether exchangeable protons, such as OH or NH, are visible on a 1H NMR spectrum. The advantage of eliminating any contribution from an exchangeable proton(s) is to simplify spectral interpretation. One disadvantage of not seeing exchangeable protons is the deficiency to the total proton count in establishing the molecular formula....

Arvin Moser
Misconstrued coupling patterns on a 1H NMR spectrum can halt an elucidation process in its track. As such, structural connectivity is best validated with additional data such as a 1H-1H COSY. A good use of coupling patterns and coupling constants is at the end of the elucidation process. Candidate structures can be verified or eliminated...

Arvin Moser
Peak shape, and subsequently the observed coupling pattern, is highly dependent on a range of factors such as temperature, concentration, pH, FID processing, etc. Relying solely on a 1H NMR spectrum for structure determination can lead into the risky realm of misinterpreting a coupling pattern. One of the simplest solutions to most elucidations is to...

Arvin Moser
Yes, it is possible to elucidate an unknown with just a 1H NMR spectrum but only for specific cases*. Case 1: an unknown with a low molecular weight and a “well-resolved” 1H NMR spectrum. Case 2: the unknown has been identified previously, or at least part of it, in a database/library/literature and a spectrum search...

Arvin Moser
One of the trickiest parts of interpreting a 1H-13C HMBC is deciding whether a 13C resonance is coinciding with another 13C resonance, i.e. overlapping 13C peaks. A past blog, Part 1, describes a specific case where the possibility of two coinciding 13C resonances can be deciphered based on a high carbon correlation count. Herein, we...

Arvin Moser
When dealing with a structure elucidation problem where little or no previous fragment information exists, the number of possibilities can seem endless. Although typically one envisions a neutral compound for the unknown, ionic compounds, such as salts and zwitterions, are also just as likely and thus can add to the complex nature of an elucidation....

Arvin Moser
The approach behind solving a structure elucidation problem is very similar to attempting a math problem or working on a jigsaw puzzle. This similar mental framework shares a basis, but not limited to, on understanding the basic rules that define the problem, and in some cases the creativity and flexibility to redefine the problem. When...

Arvin Moser
Chemical shift information offers a clue into an atom’s hybridization state. For example, carbon atoms with a carbon chemical shift greater than 90 ppm are typically considered as sp2 carbons. If 4 sp2 carbons are present, one can infer 2 alkene pairs. Five sp2 carbons and an available oxygen and nitrogen atom suggest the possibility...

Arvin Moser
A common misinterpretation of 2D NMR data can occur when dealing with weak correlations. Weak correlations are commonly introduced in how the sample is prepared or how the data is collected or processed. Examining the spectrum down to level of the density matrix can ensure all correlations are picked up. The 1H-13C HMQC below shows...