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ACD/Labs Blog

Arvin Moser
Spectral data that exhibit weak signals (low S/N) can easily be misinterpreted. A good approach is to check the data against other data to confirm whether the signal is real or an artefact. For an unknown compound, the 1H -13C HSQC spectrum below is shown at two different intensity thresholds. The aromatic protons at 6.97...

Arvin Moser
With deuterated chloroform, the signals from the solvent can overlap with the signals from the unknown of interest. The following spectra are some examples one may encounter. In the expanded regions for each 13C NMR spectrum, Cases 1, 2, 3, 4 and 5 display a weak signal at ~76.8, 77.3, 77.5, 77.5, 77.5 ppm, respectively....

Arvin Moser
Solvent signals that overlap with signals from the unknown can be a hurdle in an elucidation. The energy wasted when misidentifying a signal can make an elucidation attempt wearisome and frustrating to put it mildly. Several 13C NMR spectra were collected in deuterated chloroform for a set of unknown compounds. Are any non-solvent signals evident...

Arvin Moser
For this puzzle, the objective is to extract structural information from the NMR data. However, the underlying message is to check all possible atomic combinations so that no plausible fragment gets overlooked. For an unknown compound, an expanded region of the 1H-13C HSQC-DEPT spectrum below shows two 1H multiplets and two negatively-phased correlations (blue). The...

Arvin Moser
For each increment of zero filling, the number of data points defining a line shape is increased. The trade-off is the size of the FID increases proportionately. An FID with 1K = 1024 points will produce a file of ~ 50 kb (including data parameters). The goal is to balance the file size with the...

Arvin Moser
Zero filling is the process of adding a string of zeroes to the end of an FID. The following puzzle aims at understanding how zero filling impacts the line shape of a doublet. The following 1H NMR spectrum was collected with a total of 4K points (selective region is shown as spectrum E). Applying different...

Arvin Moser
Piece by piece, fragment by fragment, an unknown compound is constructed until it is solved. The purpose of this puzzle is to focus on solving a fragment. The 1H-13C HSQC spectrum, shown below, is for an organic three-carbon fragment. The fragment is known to have 2 open sites that connect back to the structure. What...

Arvin Moser
As more information is needed to solve an unknown, it becomes useful to understand what information is available, make a hypothesis and then get to the grunt work of eliminating the unlikely candidates. Below is a summary explaining some of the information that can be extracted from the problem set. Given an unknown compound as...

Arvin Moser
It is fairly route for an elucidator investigating an unknown compound to relate data from multiple spectroscopies. This puzzle aims at establishing a molecular formula from a set of spectroscopic data. For an unknown organic, a ESI(neg.)-ToF mass spectrum for a singly-charged species and a 13C NMR spectrum are supplied below. In addition, the 1H...

Arvin Moser
Tying together the information from a 1H NMR and COSY spectrum, an elucidator can piece together certain fragments. Below is the solution for Logic Puzzle #21. The 1H NMR spectrum shows four aromatic methine multiplets at 6.61, 7.15, 7.22 and 7.58 ppm with coupling constants less than 2.5 Hz. The small coupling constants points to...