# ACD/Labs Blog

## Logic Puzzle #16: Can you spot the Impurity(s)?

Even with ‘good’ data, every elucidation of an unknown offers the potential for impurities to hinder the process. The task develops into differentiating signals pertaining to an unknown from the impurities. The 1H NMR and 1H-13C HSQC spectra below are for an unknown (solvent signal not shown). Are all the signals from a single unknown...

## Logic Puzzle #15: Multiple Molecular Formulae … Solution

An effective elucidator is capable of connecting information from multiple sources with the goal of eliminating the inconsistent candidates. In this puzzle, the candidates are molecular formulae (MFs). The previous blog listed 4 potential MFs differing in mass difference and RDBE. The mass difference is not a good filter as the mass differences for the...

## Logic Puzzle #15: Multiple Molecular Formulae

When the spectral data is sparse, the list of potential candidate structures can seem endless. The task then becomes sifting through the spectral data as a means to filter the candidates. The purpose of this puzzle is to perform such a task. The following unknown compound with a mass of 380.1 +/- 0.5 Da comprises...

## Logic Puzzle #8: Strong Coupling or Peak Overlap? … Solution

There are two approaches to deciding which scenario best fits the NMR data in the puzzle. A structure elucidator can provide evidence that one scenario is more probable than an other and/or eliminate one scenario on the grounds of insufficient/contradictory data to support it. For the following 1H NMR spectrum, if the integral of the...

## Logic Puzzle #8: Strong Coupling or Peak Overlap?

The goal of this puzzle is to distinguish between strong coupling and peak overlap. For the following 1H NMR spectrum, are the 1H signals at 7.58-7.59 ppm exhibiting strong coupling or are they two overlapping multiplets or both?

## Logic Puzzle #7: Almost Missed It … Solution 2

With intense solvent signals present on a spectrum, a smaller signal(s) can easily be missed. If 2D NMR data is available, then this extra information can assist in clarifying whether a small signal(s) is obscured by larger signals. On the 1H-13C HMBC below, the correlations for CDCl3/CHCl3 (due to 1J coupling responses and more) are...

## Logic Puzzle #5: Coupling + Tilting + Integration = Benzene … Solution

The goal of this puzzle is to determine the respective benzene ring systems that would exhibit the following 1H NMR spectrum. The number of substituted benzene ring systems that would exhibit the following 1H NMR spectrum is 3 (assuming no repeating units). The keys to solving this puzzle lie with the determination of which multiplets...

## Logic Puzzle #5: Coupling + Tilting + Integration = Benzene

The goal of this puzzle is to determine the respective benzene ring systems that would exhibit the following 1H NMR spectrum. For the following aromatic region of the 1H NMR spectrum, how many benzene ring systems are present?

## Logic Puzzle #4: Correlating to the Correct 13C Signal … Solution

The goal of this puzzle is to resolve the ambiguity exhibited within a 2D NMR spectrum and thus provide the correct signal correlation. Although this exercise may seem a trivial one, it is important to go over the rationale when correlating one signal to another. For the following 1H-13C HSQC-DEPT NMR spectrum it is important...

## Logic Puzzle #4: Correlating to the Correct 13C Signal

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...