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ACD/Labs Blog

Arvin Moser
The goal of this puzzle is to resolve the ambiguity exhibited within a 2D NMR spectrum and thus provide the correct signal correlation. The following 1H-13C HSQC-DEPT NMR spectrum shows two one-bond correlations linked to the 1H signals 2.75 and 3.50 ppm and two closely spaced 13C signals at 61.5 and 62.2 ppm. Does the...

Arvin Moser
A great skill to master is the capability to conceptualize a fragment or structure directly off a spectrum without resorting to paper-and-pen work. This skill is learnt through lots of practice. Whenever partial information is available, an elucidator can conjure up a mental image of possibilities and should it be required instinctively hunt for any...

Arvin Moser
There are many advantages in working with a 1H-13C HSQC-DEPT spectrum over a 13C DEPT-135 and a 1H-13C HSQC (see Post 1 & Post 2). In most cases, a 1H-13C HSQC-DEPT is more valuable than either one of those experiments. The aliphatic region of a 1H-13C HSQC-DEPT is spectrum below. Two coincidental carbon signals are...

Arvin Moser
Part 1 presented a challenge to determine an experiment to distinguish two very similar products from each other, namely 3-methyl-5-(pyridin-2-yloxy)pyridine and 5′-methyl-2H-1,3′-bipyridin-2-one. The products have identical formula weights and the LC/MS and 1H NMR are too similar to draw any conclusion from. The first step is to determine what is different between the two products...

Arvin Moser
Sugar residues (saccharides) can be tough to elucidate. They tend to have 1H NMR spectrum with overlapping and sometimes poorly-resolved 1H signals, and the 2D NMR data presents lots of ambiguous assignments. With a little practice, an elucidator can quickly pick out a sugar moiety based on a minimal amount of NMR data. For a...

Arvin Moser
Where a COSY or TOCSY spectrum can be a challenge for a structure with severe spectral overlap, collecting an HSQC-TOCSY spectrum can be a better choice. An HSQC-TOCSY experiment stands for Heteronuclear Single Quantum Coherence-Total Correlation Spectroscopy and other variants include HMQC-TOCSY, HSQC-COSY, etc. Depending on the mixing time, the hybrid experiment generally offers information...

Ryan Sasaki
Above is a picture of an example output of our automated structure verification routine. This highlights one of the strengths of our automated verification approach, one Phil Keyes calls a “fringe benefit” (See slides 39-42) in that following verification, you get an estimated assignment starting point. The output is a report, or spectrum file that...

Ryan Sasaki
In yesterday’s post I pointed you to an article that has become the most accessed article of all time in the Journal of Cheminformatics, co-authored by representatives of ACD/Labs. This article is a very comprehensive outline of the different approaches, developments, and successes of the development of CASE (Computer-Assisted Structure Elucidation) systems . I hope...

Ryan Sasaki
An article co-authored by several ACD/Labs scientists, the Russian Academy of Scientists, and ChemZoo, Inc. has been generating a lot of interest over the past year. In fact, this article entitled, “Computer-assisted methods for molecular structure elucidation: realizing a spectroscopist’s dream“ is the most accessed article of all time, on the Journal of Cheminformatics website....

Arvin Moser
NOESY, ROESY, COSY and TOCSY are all 2D NMR experiments that sound so similar but offer different pieces of information about the puzzle. When interpreting the NMR data, it is important to understand how the nuclei interact with each other. For example, the presence of a cross peak (a correlation off the diagonal) on a...