NMR Archives - Page 4 of 25

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

Arvin Moser Nov 27, 2012

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!

Arvin Moser Nov 9, 2012

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

Arvin Moser Oct 29, 2012

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

Arvin Moser Oct 18, 2012

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

Arvin Moser Oct 5, 2012

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...

Logic Puzzle #35: Assigning Chemical Shifts

Arvin Moser Sep 24, 2012

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, a di-substituted phenyl ring with a fluorine substituent was deciphered. The 13C NMR spectrum below shows two 13C signals split due to 19F-13C coupling. Which carbon, chemical shift...

Logic Puzzle #34: Too Much or Too Little, Where is the Happy Middle? … Solution

Arvin Moser Aug 30, 2012

A good approach is to check and compare your experimental data before and after processing to ensure no information is lost. The 1H NMR spectrum below shows two signals at 7.34 and 7.37 ppm. At 0.2 Hz line broadening (LB), the spectrum (bottom) shows two signals as two singlets. With no line broadening, the spectrum...

Logic Puzzle #34: Too Much or Too Little? Where is the Happy Middle?

Arvin Moser Aug 3, 2012

Post data processing can both be a good thing or a bad thing. With any experimental data, too much processing can affect some critical pieces of information. A 1H NMR spectrum was collected for an unknown compound. An exponential function was applied to the data to help improve the signal-to-noise. A line broadening of 0.0...

Logic Puzzle #32: One Real, One Impurity. Which is Which? … Solution

Arvin Moser Jun 29, 2012

A subtle clue can guide an elucidator to choose one scenario over another. Given the 13C NMR spectrum below, it is apparent that either the C at 147 ppm or the CH3 at 29 ppm is an impurity based on the limit of the carbon count. Since both carbons lack any 1H-13C HMBC correlations, a...

Logic Puzzle #32: One Real, One Impurity. Which is Which?

Arvin Moser Jun 22, 2012

Given 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 carbon count is identified at 18 in total. The 13C NMR spectrum below indicates 19 carbon atoms. There are two 13C signals,...

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