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ACD/Labs Blog

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
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
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
Without a set routine to acquire a 19F NMR spectrum for every single sample, an elucidator must resort to routine NMR experiments for clues to the presence or absence of fluorine. For the elucidator who routinely acquires a proton decoupled 13C NMR, the spectrum can provide some clues into the presence of fluorine. Carbons in...

Arvin Moser
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...