Philosophy-Chemistry-Education Archives - Page 4 of 24

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 #33: Name It … Solution

Arvin Moser Jul 27, 2012

The nomenclature rules for organic compounds set by the International Union of Pure and Applied Chemistry (IUPAC) committee (http://www.iupac.org/) do offer flexibility in some areas especially in cases where old publications have old terms. Below are some examples. The answers for the structures, as based on the IUPAC nomenclature rules, are listed below. Some links...

Logic Puzzle #33: Name It

Arvin Moser Jul 17, 2012

Following a successful attempt at solving an unknown, the next step may be to determine a name for the novel compound. The nomenclature rules for organic compounds are set in place by the International Union of Pure and Applied Chemistry (IUPAC) committee (http://www.iupac.org/). For the following compounds, which names adhere to the IUPAC nomenclature rules?

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,...

Logic Puzzle #31: Are the Signals Related? … Solution

Arvin Moser Jun 13, 2012

To identify co-eluting components on a chromatogram, one searches for any distinct differences between the components. There are basically three criteria to check the XICs (extracted ion chromatograms) for to confirm whether the m/z signals pertain to the same component: line shape, signal apex and retention time range. The XICs for m/z 188.1 and 205.1...

Logic Puzzle #31: Are the Signals Related?

Arvin Moser Jun 5, 2012

Sorting out what compounds are present in a mixture is a difficult task. The process is further complicated when the compounds co-elute on a chromatographic run. An LC/MS (ESI+) was collected for an unknown sample comprising of small organic molecules. The total ion chromatogram (TIC shown in black) shows a signal at 2.86 minutes. The...

Logic Puzzle #30: Unknown Coupling Pattern … Solution

Arvin Moser May 29, 2012

Coupling patterns that overlap can be deceptively simple. There are two possible coupling patterns for the CH2 signal at 3.39 ppm (top spectrum): a singlet or two ‘doublets’ (AB spin system) tilted towards each other. The bottom spectrum shows an example of two ‘doublets’ where the outer signals at 3.34 and 3.43 ppm are barely...

Logic Puzzle #30: Unknown Coupling Pattern

Arvin Moser May 7, 2012

Coupling patterns can be deceptively simple. For an unknown compound, the expanded region of a 1H NMR spectrum below shows a signal at 3.39 ppm for a CH2 group. Is the coupling pattern for this two spin system a ‘true’ first-order singlet?

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