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Arvin Moser
Generally, a 1H-13C HMBC experiment offers a wealth of connectivity information about an unknown structure(s). However, an elucidator may be faced with the issue of ambiguity in assigning a correlation(s) to a 1D resonance(s). A correlation with an ambiguous assignment may be assessed in one of 5 ways: -reprocess the HMBC data using a different...

Arvin Moser
Failures, as are successes, are an integral part of a structure elucidator’s role. What differentiates a good elucidator from a bad one is the capability of an elucidator to learn from his/her failures. The most common obstacle that can hold a structure elucidation process from becoming a success is structural bias. (This is based on...

Arvin Moser
Attempting a challenging structure elucidation of an unknown and being unable to solve the problem can put a damper on a hectic workload and possibly on your skills as an elucidator. Emotionally, the excitement of working on a challenging elucidation problem leads into frustration — results are what count. Subsequently, the elucidator faces the following...

Arvin Moser
Like a methoxy group, a t-Butyl group stands out over other 1H resonances. For organic compounds, the 1H resonance for a t-Butyl group generally towers over other 1H resonances because it integrates to ~9 protons (assuming the presence of 1 t-Butyl group and no overlap with other resonances). The basic 1H NMR pattern of the...

Arvin Moser
When trying to elucidate an unknown structure using 2D NMR information, an elucidator gains an advantage by analyzing all of the NMR data as a whole rather than as individual pieces. Although complicated at first, this different perspective at viewing the NMR data can facilitate the elucidation process. The following list are a few advantages...

Arvin Moser
MS and NMR are complementary tools for structure elucidation. Knowing when to apply which tool can assist an elucidator in solving for an unknown structure quickly and with less frustration. Although the sample data below is for a simple organic structure, it is working through many simple examples that one refines the skills needed for...

Arvin Moser
Although NMR offers some strategies for determining the presence of a fluorine atom(s), fragment loss of a CF3 group can be determined from a mass spectrum. The EI MS for 2,2,2-trifluoro-N,N-dimethylacetamide (Mmi = 141 Da) is shown below. The ion peak at m/z 72 indicates the loss of a CF3 group. Although the ion peak...

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 1H-1H COSY dataset provides information on coupled spin systems. A coupled spin system does not necessarily imply that the protons are bonded to only carbon atoms . An example of an exchangeable proton (OH) coupled to a proton from a CH group is shown below. Three spectral datasets, 1H NMR, HMQC and a COSY-45...

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...

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