All Questions
Tagged with stereochemistry nmr-spectroscopy
14
questions
2
votes
1
answer
99
views
How to determine the value of the NOE from the NOESY spectrum?
I have 1D NOESY spectra from which I need to find out the value of the NOE (%). Is it enough to simply measure the intensity of the resulting peaks or is it necessary to subtract it from the ...
- 21
5
votes
3
answers
494
views
What is the relationship between Ha and Hb in the given compound, trans-1,3 dichlorocyclobutane. Are they enantiotopic or homotopic?
The question is to find the TOPICITY relationship between Ha and Hb in the given compound, (trans 1,3 dichlorocyclobutane)
They seem to be in the same chemical environment, so I tried the ...
- 371
0
votes
2
answers
489
views
Hydrogens of cyclohexanol are enantiotopic or diastereotopic, which is true?
I am studying spin-spin coupling theory in NMR. Below is an exercise from Mcmurry's organic chemistry.
The textbook says that * stands for chiral center. But is it true? When I searched for it some ...
- 1,101
3
votes
3
answers
509
views
Diastereotopic methylene protons in achiral molecules
Are the protons in methylene groups of achiral molecules such as propane-1,2,3-triol or 3-hydroxypentanedioic acid diastereotopic?
Consider propane-1,2,3-triol. To me, replacing one of the protons in ...
- 163
3
votes
0
answers
127
views
Chemical shift difference methyl groups in 4-hydroxy-2,5-dimethyl-3-hexanone
Can someone explain why the NMR Spectrum of 4-hydroxy-2,5-dimethyl-3-hexanone shows a chemical shift difference for the methyl groups at the end? Why aren't the other carbons have a difference?
Below ...
- 53
5
votes
0
answers
80
views
Is it possible to estimate the abundance of conformers from J values?
I have a system of two disubstituted cyclohexanes and I want to estimate the abundance/ratio of the two based on the J values and if possible, roughly estimate the difference in free energy.
To get ...
6
votes
1
answer
964
views
Why does the 31P{1H} NMR spectrum of cis-[Mo(CO)2(dppe)2] show two signals?
I've tried searching for literature references that explain this, finding only a single reference which refers to the two signals as originating from phosphine environments cis/trans to carbonyls, ...
- 91
2
votes
1
answer
5k
views
H-NMR Equivalent Protons and Coupling of Glycerol
I've been searching for explanations to understand why the labeled protons on carbons 1 and 3 are not equivalent in the below figure.
Another figure that shows the same results:
SDBS confirms the ...
- 21
5
votes
1
answer
10k
views
How does the Mosher ester method allow determination of absolute configuration of secondary alcohols
One of the challenges in synthesis is the correct assignment of absolute stereochemistry. This has been asked previously on chem.SE (here and here), but this question specifically asks about the ...
- 17.2k
2
votes
1
answer
4k
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Is there a way to tell which one is the racemic or meso compound with 1H-NMR if all you had was the structure and spectra?
I know that diastereomers will have different chemical shifts but can you predict which one is which via up/down field shifts in the spectra?
For instance, is it like alkenes vicinal H’s when cis and ...
- 139
3
votes
2
answers
3k
views
How to differentiate diastereotopic protons by NMR in flexible groups?
In (1R,2S)-2-(hydroxymethyl)cyclohexan-1-ol shown below, Ha and Hb are diastereotopic (they will have different chemical shifts), but because of fast rotation, NOESY should show that both couple ...
- 14.4k
2
votes
1
answer
307
views
Why are the ethyl ester methylene protons not diastereotopic in ethyl (+-)-2-methylbutyrate?
In the following compound, there is one chiral center and two methylene groups. Why are the protons on the ethyl ester methylene not diastereotopic?
- 21
7
votes
1
answer
738
views
Diastereoisomer of quinic acid and its proton NMR?
Question:
Quinic acid, A, has the gross structure shown below:
(i) Draw all the possible diastereoisomers of A and indicate which are chiral.
(ii) Quinic acid is optically active and ...
- 1,799
5
votes
2
answers
11k
views
Are the hydrogen atoms of 2-methylindane homotopic, enantiotopic, diastereotopic or unrelated?
I'm very confused. According to the answer key, the circled hydrogens of 2-methylindane (2-methyl-2,3-dihydro-1H-indene) are diastereotopic. I thought they were enantiotopic.
My thought process is ...
- 193