ACD/Labs Blog

Logic Puzzle #40: What Fragment is This?

An experienced elucidator can recognize spectral patterns and use this information to piece together a fragment. This puzzle examines one such pattern-to-fragment connection. A 1H NMR spectrum below shows the aromatic region for an unknown compound? Can you identify the fragment that would produce this pattern?

Logic Puzzle #39: Coincidental Overlap or Not? … Solution

Quaternary carbons can be tricky in identifying. Keep your options open to ensure the bigger picture is not missed. The expanded region of the 13C NMR spectrum shows 4 signals for an unknown compound. The signal at 172 ppm represents 1 or 2 amide group(s). The higher intensity of the signal at 172 ppm in...

Logic Puzzle #39: Coincidental Overlap or Not?

Spectral data is just data until you can see the bigger picture. This puzzle looks at a scenario of quaternary carbons. For an unknown compound, a standard 13C NMR spectrum (500 MHz CDCl3) was collected. The expanded region below shows 4 signals. Is the signal at 172 ppm attributed to 1 or 2 carbons (from...

Logic Puzzle #38: Count This … Solution

Yes, basic counting is important in solving an unknown. How did you stack up with this puzzle? The 13C NMR spectrum below shows 7 signals in total, 3 intense signals and 4 weak signals. The 4 weak signals follow a quartet pattern produced by a CF3 group. The unknown contains a minimum of 4 C...

Logic Puzzle #38: Count This

A key step in interpreting NMR data is in counting correctly the number of signals associated to the compound of interest. This puzzle covers one particular example. For a pure unknown compound, the 13C NMR spectrum below shows several 13C signals at varying intensities. What is the minimum C atom count?

Logic Puzzle #37: HSQC or TOCSY, the correlations both look the same! … Solution

Hybrid experiments, like an HSQC-TOCSY experiment, add an extra dimension to its interpretation. It is through practice that one can become familiar with interpreting the data easily. For an unknown compound, a 1H -13C HSQC-TOCSY spectrum was collected. There are 8 visible HSQC correlations circled in red and 10 TOCSY correlations circled in blue (numbered...

Logic Puzzle #37: HSQC or TOCSY, the correlations both look the same!

Depending on the mixing time, HSQC-TOCSY experiments generally offer information on both short-range and long-range coupled nuclei. The issue arises in sorting out the HSQC correlations from the TOCSY ones. For an unknown compound, a 1H -13C HSQC-TOCSY spectrum was collected. The expanded region of the spectrum below shows several correlations. How many HSQC-related correlations...

Logic Puzzle #36: Chemical Shifts and Carbon Hybridization States … Solution

With any unknown compound, there always seems to be lots of choices. For this unknown, it seems quite straightforward to consider the carbon of the CH group as an sp2 with a carbon shift of 113.0 ppm and proton shift of 7.0 ppm. However, there are cases where the carbon may not be an sp2....

Logic Puzzle #36: Chemical Shifts and Carbon Hybridization States

With any experimental data, producing a list of scenarios that are consistent with the data can help guide an elucidator through the problem while ensuring nothing gets overlooked. For an unknown compound, the 1H -13C HMQC spectrum shows a CH group with a correlation at 7.0 and 113.0 ppm. Is the carbon hybridization an sp2 or...

Logic Puzzle #35: Assigning Chemical Shifts … Solution

Coupling information is very useful in locating the position of an atom in relation to other atoms. This puzzle covers one such example. For an unknown compound1, the 13C assignment is not clear for carbons 116 or 134 ppm. The 13C NMR spectrum shows the 19F-13C coupling for the carbon at 116 ppm as 23.7...

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