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ACD/Labs Blog

Due to their broad peaks and wide range of chemical shifts in 1H NMR spectra, exchangeable protons are known to pose challenges in NMR interpretation, but collecting 2D spectra and selecting proper experimental conditions can sometimes be used in our favor to learn more.

1H NMR is the go-to technique to help identify or confirm the structure of organic compounds. A solution-state proton spectrum is relatively fast to acquire and a lot of information about the structure of a compound can be deduced from it. With centuries of combined experience in NMR data interpretation, we thought we’d share the basics of analyzing solution-phase 1H NMR spectra in this blog.

Coupling constants from a 1D NMR spectrum can be very useful to a chemist when trying to characterize a structure. However, there are cases where the perceived coupling constants can be misleading and thus wrong. The 1H NMR spectrum below shows several multiplets for a major component tryptophan and a minor component. For tryptophan, the...

In collaboration with Sequoia Sciences Inc., we developed a strategy for the dereplication of a complete or a partial structure using 1H NMR, 1H–13C HSQC and 1H–1H COSY spectral data, a molecular formula composition range and structural fragments against a massive database of about 22 million compounds is considered. The work was based on 18...

Many analytical data rely on common calculations. This solution shows the formula used in the calculations. NMR and MS data were collected on two unknown compounds. The TOF-MS data shows the [M+H]+ at m/z 300.0000 and 600.000 at an error of 0.001 Da. The 500 MHz 1H NMR spectrum shows two chemical shifts at 1500.00...

Logical reasoning and pattern recognition form the basis for making a pattern-to-fragment connection. For an unknown, the 1H NMR spectrum below shows 5 multiplets in the aromatic region. The multiplet at 7.57 ppm shows two overlapping multiplets: a broad signal overlapping a ‘doublet’ (noted as d*). Based on the multiplets’ tilt/lean and integrals, a 1,2-disubstituted...

An experienced elucidator can recognize spectral patterns and use this information to piece together a fragment. This puzzle examines one such pattern-to-fragment connection. A 1H NMR spectrum below shows the aromatic region for an unknown compound? Can you identify the fragment that would produce this pattern?

Post data processing can both be a good thing or a bad thing. With any experimental data, too much processing can affect some critical pieces of information. A 1H NMR spectrum was collected for an unknown compound. An exponential function was applied to the data to help improve the signal-to-noise. A line broadening of 0.0...

Coupling patterns that overlap can be deceptively simple. There are two possible coupling patterns for the CH2 signal at 3.39 ppm (top spectrum): a singlet or two ‘doublets’ (AB spin system) tilted towards each other. The bottom spectrum shows an example of two ‘doublets’ where the outer signals at 3.34 and 3.43 ppm are barely...