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ACD/Labs Blog

Arvin Moser
A 1H-1H COSY dataset of an unknown structure with protons offers many combinations of atom connectivity. The goal for the elucidator is to assess the correlations and narrow down a set of fragments that support the data. Below is a structural list for 1H to C to 1H connectivities. Absent from the list, heteroatoms such...

Arvin Moser
A component of structure elucidation involves the capability to interpret spectral data of an unknown compound. The interpretation of the data generally leads into a wide range of structural possibilities for the unknown. The goal of the elucidator is to narrow down the structural possibilities to a minimum set of fragments. Taking these fragments, the...

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....

Ryan Sasaki
In fact, to borrow a phrase from a colleague, this might be the defacto article on Computer Assisted Structure Elucidation (CASE) for the next decade! This article written by Mikhail Elyashberg, Antony Williams, and Gary Martin spans across two issues of the review journal, Progress in Nuclear Magnetic Resonance Spectroscopy.  This article entitled, entitled, "Computer-Assisted...

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...

Arvin Moser
Experiments such as 1H-13C HMQC, HSQC, or HETCOR can be used to suspect the presence of fluorine but not necessarily rule out the absence of fluorine. The stipulation behind this assessment is that a carbon from either a CH, CH2 or CH3 group must experience 13C-19F coupling(s). The spectrum below is a region of an...

Arvin Moser
When faced with a crowded region in a 1H NMR spectrum, a 2D NMR experiment can assist in removing the ambiguity and in narrowing down the proton count. For the 1H NMR spectrum below, Multiplet F (the region between 1.4 to 1.8 ppm) displays an integral of 6.71. Although several factors may contrbute to the...