Questions tagged [stereochemistry]
Applicable to questions about the spatial arrangement of atoms in a molecule and how they affect its physical or chemical properties.
725
questions
2
votes
1answer
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Confusion in R/S Nomenclature and Chirality
I have many confusions regarding optical isomerism:
What is the use of the R/S nomenclature? I understand that it is used to distinguish between the different spacial arrangements that are possible ...
-3
votes
0answers
27 views
Conversion of a compound to a racemic mixture of enantiomers [closed]
I am studying for the GRE Chemistry and came across this question. I was not sure how to proceed with it. The answer is A but I do not know why. It has been a little bit since Organic chemistry, but I ...
-3
votes
0answers
26 views
How Mabcd type co-ordinate compound exhibiting geometrical isomerism without having 2 identical identical ligand [closed]
According to my understanding ,2 co-ordinate compounds are considered as -cis or -trans form based on the spartial arrangement of 2 identical ligands but in the co-ordinate compound of Mabcd (square ...
0
votes
2answers
112 views
How many stereogenic centers exist in the atropine?
I'm pretty sure that both C bonded to N are stereogenic centers. I don't know about the others, any help? Is this correct?
-1
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0answers
26 views
How much can the photoisomerization wavelength of a molecule be redshifted by the addition of conjugation?
Adding electron withdrawing groups or conjugation will redshift the wavelength requiered to photoisomerize a molecule. However, how much can this really be used push the frequency down? What is the ...
1
vote
0answers
33 views
How do molecules with opposite rotational photoisomerization bonds behave? [closed]
If a molecules bond change upon isomerization with the respective bonds straining the molecules as they orient themselves opposite from each other, would the molecule undergo some kind of ...
7
votes
1answer
272 views
Does 1,4-dimethylcyclohexane have a chiral center?
My textbook says that 1,4-dimethylcyclohexane (cis or trans) does not have a chiral centre, since two groups on the tertiary carbon (that are the part of the ring) are identical, and thus the compound ...
2
votes
1answer
160 views
Why is [M(AB)2] a geometrical isomer?
Our teacher told us that for coordination number 4 and tetrahedral shape $\ce{[M(AB)2]}$ doesn't have a plane of symmetry, so it shows optical isomerism.
What if we take a plane passing through the ...
-2
votes
1answer
49 views
How many conformations are possible for ethane?
I am talking on the basis of observations made on the Newman projection of ethane.
According, to the various sources, that I found on many websites, the number of conformational isomers are 2. They ...
4
votes
1answer
80 views
Is the SN1 reactions stereospecific or stereoselective? [duplicate]
In the SN1 reaction, the product show retention and inversion. Since one of them is major unless it forms a racemic mixture, does it mean that the SN1 reaction is stereospecific?
9
votes
2answers
648 views
Determining if the product would be cis or trans after an anti elimination on fischer projections
I find these kind of problems really confusing for some reason, but I saw a way on the web and tried doing it that way:
I considered the basic Fischer operations (Vertical: Below the plane of paper, ...
2
votes
1answer
44 views
Could Gaussian or Spartan software determine stereoisomers from conformational landscape of a molecule alone?
I read that, on some papers, conformers were generated by stereoconfiguration of the molecules and from there, they evaluated stability of each stereoisomer in terms of free energy differences between ...
2
votes
1answer
38 views
How do I label stereogenic centers R or S when there are 3 bonds in the plane and 1 bond coming out?
I need help with question (d). I labeled the O the first priority, then the C that's bonded to an O the 2nd, and the C above that is attached to 3 other C's the 3rd priority. So, I ended up getting S, ...
3
votes
0answers
38 views
Labelling of molecular motor isomeric forms as trans and cis
I am reading Koumura et al. (2002), a paper about molecular motors. It contains this figure:
Being an absolute layman when it comes to naming my molecules I'm a little confused as to why the left ...
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votes
1answer
46 views
How do you know if a compound with only one stereogenic center is trans or cis? [closed]
I understand that both of these compounds are R but I do not understand why A is trans and C is cis.
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votes
1answer
60 views
D and L configuration of monosaccharides
I got this question in the last week's test from Organic Chemistry.
I am a bit confused in assigning D and L configuration.
Help me understand the topic of D and L configuration and help with this ...
6
votes
2answers
551 views
Why do Enantiomers have different chemical properties with optically active reagents?
As I understand Enantiomers have similiar physical properties but they do show different chemical properties with optically active reagents. This point is something which I am not able to logically ...
3
votes
3answers
374 views
Chiral center or not? Similar substituents, but still two possible structures!
As far as I know, the central carbon shouldn't be a chiral center because it has two identical substituents. And yet, these two compounds should be different from each other.. Is it possible to denote ...
0
votes
0answers
30 views
Does this molecule show cis-trans isomerism? [duplicate]
I want to find if the above molecule shows cis-trans isomerism, per an assignment. I am assuming that such isomerism, if present, will be shown by the substituted chlorines.
It seems clear to me that ...
1
vote
0answers
42 views
How does optical activity work? [duplicate]
I have learnt that chiral molecules are able to show optical activity; that is, they are able to rotate plane polarized light by some angle.
But how does it actually happen? Won't the orientation of ...
4
votes
1answer
60 views
Why is the A-value of methoxy group lower than that of the hydroxyl group?
I am studying conformational analysis of monosubstituted cyclohexane. "A-value" refers to the energy difference between conformers with substitutent in equatorial (more favored) and axial ...
6
votes
1answer
154 views
Stereoisomers of 1,3,4,6-tetramethylcyclohex-1,4-diene
How many stereoisomers are possible for following compound (1,3,4,6-tetramethylcyclohex-1,4-diene)?
My Approach
the 1,4 methyl groups lie in the plane, whereas 3,6 are possible chiral centers. ...
4
votes
1answer
275 views
Odd/Even swap rule for chiral compounds in stereochemistry
I had this question asked in my exam, where I was supposed to find if this pair is a diastereomer:
Now, I have learnt this rule where: Making odd number of swaps in a molecule means they both are ...
3
votes
1answer
200 views
R or S configuration?
The respective configutations of a and b are...?
I tried to find the answer for a (for me is: 2S, 3S) but I'm not sure of my results, can someone help me?
5
votes
0answers
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Does PubChem have stereocenter location data?
I have spent the last couple of days learning to navigate, find useful information and use the download service on the PubChem website. One of the pieces of information you can find is a stereocenter ...
3
votes
2answers
51 views
Diastereomers - cyclic compounds [closed]
Why in this problem there isn't a diastereomer with the $\ce{-CH3}$ in the back (dash) and the $\ce{-CH2CH3}$ in front (wedge)?
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votes
1answer
50 views
Enantiomers and diastereomers [closed]
I don't understand why on the problem a. B and C are enantiomers, while on the problem b. B is identical to the last molecule.
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0answers
70 views
Determining priority for a cyclic compound [duplicate]
I have problem in determining the CIP priorities in (S)-ketamine.
What is the order of priorities for esketamine? Does the carbon bonded to the ring with chlorine have higher priority compared to the ...
4
votes
1answer
201 views
Assigning E–Z configuration for alkenes with cyclic substituent groups [duplicate]
I was taught that according to CIP rules, we must check the priority order for the substituents. But how can we do the same for molecules with cyclic groups as substituents?
How do we compare the ...
2
votes
1answer
220 views
How can a compound having a plane of symmetry be Chiral?
The compound( Given in the image below) is treated with $\ce{excess H2 in Pt}$.
Here, (a) - The given compound. (b) - What the answer should be according to me.
(c) - What the actual answer is:
Q1 - ...
1
vote
0answers
22 views
How do electrostatic effects effect facial selectivity in addition to cyclic oxo-carbeniums?
I was reviewing Dave Evans' notes for stereochemistry of C=X electrophile additions, and found this slide detailing differences in additions to cyclic oxo-carbenium electrophiles, but I don't ...
4
votes
1answer
80 views
How is chirality center defined for an atom with 5 substituents?
I understand that carbon atoms normally only have up to 4 substituents and the R and S chirality centers are defined for 4 substituents. Is there a similar convention of 'chirality' for an atom with 5 ...
6
votes
4answers
674 views
Ramachandran plot Phi(ϕ) Psi(ψ) dihedral angle Convention for Zero, Positive and Negative value- old and new
Update: possible duplicate: What is the precise definition of Ramachandran angles?. Question modified.
G.N. Ramachandran et al, in their own work (PMC) (DOI), did not used phi(ϕ) and psi(ψ) as we use ...
4
votes
1answer
72 views
Does syn-dihydroxylation form racemic mixture?
I have been asked to determine the nature of the product for the following reaction:
And as I recognized this reaction to be a case of syn-dihydroxylation, my obvious response was that the product ...
3
votes
0answers
31 views
Does optical isomerism fall under the category of stereoisomerism?
I have been asked to find the total number of dichlorination products (including stereoisomers) for the following reaction:
I have figured out nine possible structures out of which two are optically ...
-3
votes
2answers
122 views
Enantiomers or identical structures?
What is the relationship between the following pair of molecules? Is the underlined answer correct? Explain.
I'm getting mixed answers. Some say these are identical molecules. Other say these are ...
0
votes
3answers
78 views
What exactly is a 'chiral centre' in a carbon compound? [duplicate]
The typical progression (in books, YouTube videos) of explanation of chiral carbons in a compound is as follows:
Chiral compounds are non-superimposable by their mirror-image;
It is easily seen that ...
0
votes
0answers
64 views
Which would have higher priority according to CIP rule (Cyclic Substituents)? [duplicate]
So if we were to assign E-Z nomenclature to this compound :
then the Ethyl group would obviously have more priority than methyl group, but I am confused whether out of Cyclopropane and Cyclobutane ...
0
votes
0answers
47 views
What are the limitations of the D, L system and the (+), (-) system for naming organic compounds
In organic chemistry, both the D, L system and the (+), (-) system are widely used, in conjunction with the modern (R, S) system.
The D, L system names an organic molecule based on the direction that ...
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0answers
51 views
In a pair of diastereomers, which of the following is true?
While going through my book, I came across this question and got really confused. Here's what the problem was:
In a pair of diastereomers,
Both can be laevo-rotatory or both can be dextro-rotatory
...
3
votes
0answers
51 views
Fischer's projection, enantiomers and diastereomers
Given Fischer's projections of a few stereoisomers of some compound, how can we find out if they are enantiomers, diastereomers, etc.? From what I understand, we can rotate the projections to have the ...
1
vote
1answer
107 views
Does anyone know what program was used to make this molecular structure picture? [closed]
I am a quantum chemistry beginer, and this picture color scheme is classic. I wonder how to make such pictures by myself.
3
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0answers
50 views
What happens when tran-2-butene reacts with aqueous bromine in the presence of chloride?
$\ce{Br2-H2O}$, containing some $\ce{NaCl,AlCl3}$ ?
I initially though that there would be anti addition of Br and OH to give 3-Bromobutan-2-ol but then I also got the intuition that NaCl might ...
4
votes
0answers
50 views
Does the chlorination of 4-methylcyclopentene generate two enantiomers or two diastereomers?
Does the chlorination of 4-methylcyclopentene generate two enantiomers or two diastereomers?
I think it makes two enantiomers (or one pair of enantiomer) since the starting compound is achiral, but ...
2
votes
2answers
123 views
How to draw chair-form for trans-decalin (with slight variation)?
I understand how to draw chair form for trans-decalin (figure 1) for the usual structure, but I am having difficulty if taken as shown in figure 2 wherein the hydrogens at bridge-head carbons are in ...
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vote
0answers
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Why does hydrogenation of this compound not result in a diastereomeric mixture? [duplicate]
In a question, this compound was given and it was asked:
"Hydrogenation of the above compound in the presence of poisoned Palladium catalyst gives?"
When I was answering it, I thought that ...
0
votes
0answers
31 views
Is 1,1,2,2-tetramethylcyclohexane not meso? (And visualizing cis-1,2-dimethylcyclohexane)
Considering the fact that cis-1,2-dimethylcyclohexane is not meso, does that mean that 1,1,2,2-tetramethylcyclohexane is also not meso?
I'm also having trouble understanding how the chair ...
2
votes
2answers
77 views
How do we know the natural abundance of isotopes on Earth?
Without knowing the Average Atomic Mass or the percent abundance, how do we know that Protium is the most prevalent hydrogen isotope? What methods did scientists use to come to this conclusion? How ...
3
votes
0answers
59 views
Stereochemistry of the product of crotonic acid with bromine
Is there a a simple rule for determining the stereochemistry for the product of a reaction between an unsymmetrical alkene like (2E)-but-2-enoic acid and bromine (anti reaction)?
If it's an anti ...
7
votes
1answer
599 views
Why are complexes of type MA3B3 not optical active?
Complexes of type $\ce{MA3B3}$ have two geometrical isomers, namely:
fac-isomer
mer-isomer
If we look closely at the mer-isomer, it has a plane of symmetry, so it is optically inactive.
But the fac-...
