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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
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...

Ryan Sasaki
In my last post I provided my excuse for not blogging much as of late. In addition to that news, I have some other news to report. Over the past 5-6 weeks I have transitioned to a new role and I am now the NMR Product Marketing Manager for ACD/Labs. This role comes with many...

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
Without correctly identifying the molecular ion on a mass spectrum, the nitrogen rule generally cannot be applied to any arbitrary ion peak. The chemical structure for N-[(1E)-1-phenylethylidene]methanamine and its EI mass spectrum are shown below. As expected, the odd value for the molecular ion at m/z 133 dictates an odd number of nitrogen atoms. However,...

Arvin Moser
For MS data, the ionization method will dictate how the nitrogen rule is applied. For example, if the ionizer is Electron Impact (EI) ionization, then the nitrogen rule is to be applied to the molecular ion [M]+* as follows: -an odd nominal mass indicates an odd number of nitrogen atoms, e.g. 1,3,5 -an even nominal...

Arvin Moser
The purpose of the nitrogen rule is to assist with deciphering how many nitrogen atoms are present without any prior information on the molecular formula. Depending on the ionization mode, an odd nominal mass indicates an odd number of nitrogen atoms, e.g. 1,3,5, whereas an even nominal mass indicates an even number of nitrogen atoms,...

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...

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