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ACD/Labs Blog

Arvin Moser
When dealing with a structure elucidation problem where little or no previous fragment information exists, the number of possibilities can seem endless. Although typically one envisions a neutral compound for the unknown, ionic compounds, such as salts and zwitterions, are also just as likely and thus can add to the complex nature of an elucidation....

Arvin Moser
The approach behind solving a structure elucidation problem is very similar to attempting a math problem or working on a jigsaw puzzle. This similar mental framework shares a basis, but not limited to, on understanding the basic rules that define the problem, and in some cases the creativity and flexibility to redefine the problem. When...

Arvin Moser
Chemical shift information offers a clue into an atom’s hybridization state. For example, carbon atoms with a carbon chemical shift greater than 90 ppm are typically considered as sp2 carbons. If 4 sp2 carbons are present, one can infer 2 alkene pairs. Five sp2 carbons and an available oxygen and nitrogen atom suggest the possibility...

Arvin Moser
A common misinterpretation of 2D NMR data can occur when dealing with weak correlations. Weak correlations are commonly introduced in how the sample is prepared or how the data is collected or processed. Examining the spectrum down to level of the density matrix can ensure all correlations are picked up. The 1H-13C HMQC below shows...

Arvin Moser
A previous blog described how a sodiated ion peak can be used to locate or calculate the molecular ion for an unknown compound. In a similar fashion, the dimer ion peak can be used to identify the mass of the unknown even if the molecular ion is no visible. The ESI+ MS data below shows...

Arvin Moser
In addition to using chemical shift information to ascertain a carbon’s proton count (i.e. C, CH, CH2 or CH3), 13C NMR experiments can be set up in a variety of ways to assist with this process. The following simulated spectra compare a variety of 13C NMR experiments for aspartame. Please note that there are variations...

Arvin Moser
A previous blog described the Internet as a valuable tool in searching for previous work based on a molecular formula. In addition to searching the Internet “directly”, certain online sites can assist and facilitate the search process. Some of these sites are free while others have a fee. Be aware that the Internet is full...

Arvin Moser
Searching for unknowns across an internal library or database can serve as a major time saver. A more accessible database is the Internet. Many chemists and elucidators search the World Wide Web using a mass, a molecular formula or a fragment. Be aware that proprietary data sent over the Internet runs the risk of being...

Arvin Moser
In a previous blog, the atoms C, H, O, and N were limited to a specific range, 0-50, 0-100, 0-10 and 0-10, respectively. Starting from a wide atom count range ensures molecular formulae are not overlooked. The ranges for the atom count can be restricted further using additional information such as NMR, IR, etc. A...

Arvin Moser
With a monoisotopic mass identified from a mass spectrum, the next step is to fit a molecular formula (or elemental composition) to the unknown. For organic compounds, the starting elements of choice are Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulfur. Information from starting material and known derivatives can also help when deciding what elements and...

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