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ACD/Labs Blog

Arvin Moser
MS and NMR are complementary elucidation tools. Knowing when to apply the correct tool can facilitate the elucidation process. Compounds with bromine atoms exhibit a distinct ion pattern on a mass spectrum. The A+2 peak for a monobrominated compound appears at almost identical intensity to the 79Br peak due to the presence of 81Br (~49.3%...

Arvin Moser
Although peak crowding can be a nuisance, a monosubstituted benzene fragment can be identified by a 1H NMR. A good marker for a monosubstituted benzene ring, and thus how an elucidator can clue in to its presence for an unknown, is whether the sum of the relative integrals for the aromatic resonances add up to...

Arvin Moser
Typically, structure elucidation via NMR can be ascribed by a stepwise workflow: 1. a sample is prepared for NMR, 2. the NMR instrument is optimized for data collection, 3. NMR data is acquired, 4. the spectral data is processed, 5. the spectral data is searched/compared to an internal database for possible hits or similarities, 6....

Arvin Moser
A calculated neutral loss spectrum is obtained from a mass spectrum by determining the mass differences between the precursor ion m/z and each of the other peaks in the spectrum and plotting the original intensity versus neutral mass. Neutral losses with small masses have limited possibilities for their composition and thus can facilitate the identification...

Arvin Moser
Every analytical instrument will give an answer; whether that answer is right or wrong or the power is off is a different story. Knowing how to troubleshoot an instrument or setup a specific experiment can be just as important as knowing how to interpret the data resulting from that instrument. A great way to learn...

Arvin Moser
Methoxy groups have a distinct NMR signature that make them easy to spot in virtually every case. The basic pattern is a singlet integrating to 3 and ranging between 2.4 to 4.4 ppm on a 1H NMR spectrum (assuming no overlap with other resonances). On the 13C end, a 13C resonance is seen between 46...

Arvin Moser
An integral part of an elucidation is to recognize and associate an NMR spectral pattern to a structure or fragment. A challenging elucidation can be simplified by being aware of as many as possible NMR patterns. One example is morpholine; it typically shows a distinct NMR pattern. A portion of the 1H-13C DEPT-HSQC spectrum for...

Arvin Moser
2D NMR experiments such as 1H-13C HMQC, HSQC, and HETCOR spectra, offer the elucidator the opportunity to assess the presence of a fluorine atom(s). The 1H -13C HSQC spectrum below is another case where a protonated carbon that experiences 13C-19F coupling shows a unique correlation pattern. The CH carbon projected on the F1 domain at...