# ACD/Labs Blog

## Logic Puzzle #26: Elemental Analysis to Empirical Formula

Elemental analysis is an experiment used to determine the elemental composition of an unknown compound. The purpose of this puzzle is to use the percentage composition data from elemental analysis to deduce an empirical formula. An elemental analysis was collected for an unknown organic compound. A 0.30 g sample of the unknown was burned to...

## Logic Puzzle #23: That’s a Fragment? … Solution

With each piece understood, a fragment(s) will emerge. From the 1H-13C HSQC spectrum, there are 3 CHn groups where n represents 1, 2 or 3 protons. The proton integrals indicate 2 CHs and 1 CH3 group. The CH3 group is observed as a singlet with 1H and 13C chemical shifts at 3.35 and 56.93 ppm;...

## Logic Puzzle #22: The Art of Uncovering the Molecular Formula

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...

## 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 #9: Does my Unknown contain Br, Cl, S and/or Si atoms? … Solution 2

Atoms like Br, Cl, S and Si present distinct isotope patterns on a mass spectrum. The isotope pattern for a single Br or Cl atom tends to be relatively straightforward and can be viewed directly off the spectrum. In the case for S and Si atoms, a little math is generally required to reveal their...

## Logic Puzzle #9: Does my Unknown contain Br, Cl, S and/or Si atoms? … Solution

There are two approaches to solving this problem set. The “quick” approach is to subtract the mass of 10 carbon atoms from the mass of the molecular mass and see if the difference can account for the atoms Br, Cl, S and/or Si. The “longer” approach is to examine the isotope patterns on the MS...

## Logic Puzzle #6: Dealing with an Extra 13C Peak … Solution

Socrates is known for saying ‘Know thyself’, along the same line, chemists should ‘Know thy instrument’. The example below is one such case. The 13C NMR [1H] spectrum below exhibits 6 signals. If an unknown compound comprises of 7 carbon atoms, then the following scenarios, or combinations thereof, are possible to account for missing or extra...

## Logic Puzzle #3: A Play on the Molecular Formulae

The goal of this puzzle is to determine how the molecular formulae of the intermediates may assist in reasoning out the final product. In this puzzle, let’s consider the following one-pot synthetic reaction (solvents and additional reactants are not shown). The molecular formula (MF) and the RDBE information are also presented. The chemical reaction illustrates...

## Ah Sugar, Sugar … Residue

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...