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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...

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...

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...

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...

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...

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...

Ideally, identifying whether a fluorine atom(s) is present is as simple as acquiring a 19F NMR. However, running ‘uncommon’ experiments is not usually my first step in an elucidation (MDE). Imagine a scenario where the elucidator is unsure whether fluorine is present. He/she acquires a 19F NMR and sees no 19F resonances. Therefore the extra...

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...

A very useful bit of information on the proton count comes from integrating a 1H NMR spectrum. However, overlapping resonances can make integration less than straightforward and in some cases ambiguous. Integration involves the following decisions to be made by the elucidator: which resonances to integrate, where the integral begins and ends, and what the...

Here is a lesson I learnt over time while working on small molecules—my Elucidation Evolution. Thinking back to when I started doing elucidations of unknowns, my mindset was to collect loads of data (NMR, MS, IR, etc.) whether I needed it or not. Initially inexperienced, I was extracting bits and pieces of information from various...