Questions tagged [stereochemistry]
Applicable to questions about the spatial arrangement of atoms in a molecule and how they affect its physical or chemical properties.
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What is Bent's rule?
I'm all bent out of shape trying to figure out what Bent's rule means. I have several formulations of it, and the most common formulation is also the hardest to understand.
Atomic s character ...
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How does Walter White make pure crystal meth using a non-stereospecific reaction?
In the highly-rated TV series, Breaking Bad, Walter White, a high school chemistry teacher recently diagnosed with cancer, takes to making the illicit drug, crystal meth (methamphetamine), by two main ...
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How to derive these general formulae for number of stereoisomers of a compound with a possible plane of symmetry?
These formulae are used if the molecule has a possible plane of symmetry. One such example would be:
Here the carbons marked with an asterisk are stereogenic centres (the asterisk is not used to mark ...
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Why is 1-ethylidene-4-methylcyclohexane chiral?
As far as I can tell, there doesn't seem to be a chiral carbon in the compound, 1-ethylidene-4-methylcyclohexane. The C-4 of the cyclohexane ring has two groups with exactly the same connectivity, and ...
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How do you separate enantiomers?
There are some stereochemical reactions that result in the presence of enantiomers. When moving forward with a practical organic synthesis, how does one usually separate them in order to continue with ...
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How to assign E/Z configuration according to the Cahn-Ingold-Prelog rules when subsituents differ only by stereochemistry
I stumbled-upon this compound:
I'm wondering how to determine the configuration of the double bond. Is it E or Z? How do I decide on the priorities when the substituents can only differ in the ...
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What is the difference between D and L configuration, and + and −?
What is the difference between D and L configuration, and + and −?
My textbook says they are two different things.
It also says that the correct way to name glucose is D(+)-glucose.
Could someone ...
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Is cis-1,2-dimethylcyclohexane a meso compound?
I was watching a video lecture today on hydrocarbons and came across this. The instructor says that, as there is a plane of symmetry, cis-1,2-dimethylcyclohexane is a meso-compound:
However, the ...
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What does lowercase r-s notation mean?
I came across a naming convention which I haven't seen before. I let ChemDraw name the following compound for me and got a name containing lowercase "r" and "s" configurations.
Can someone tell me ...
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Can heteroatoms with lone pairs be chiral centres?
If a compound has a carbon atom with four different groups covalently bonded to it, it is called asymmetric and enantiomers of the compound can exist.
But imagine if one has a different central atom, ...
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Why is trans-cyclooctene chiral?
How does trans-cyclooctene exhibit chirality if there are no stereocenters?
Related follow-on questions:
Are all higher cycloalkenes chiral?
Do more double bonds cause a bigger number of ...
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Why are allenes chiral?
How is 1-bromo-3-chloropropa-1,2-diene ($\ce{BrHC=C=CHCl}$) chiral? It doesn't have any carbon that is connected to four different groups.
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Why is the inversion barrier larger in PH3 than it is in NH3?
The inversion barrier in $\ce{NH3}$ is approximately $5~\mathrm{kcal~mol^{-1}}$ and that of $\ce{PH3}$ is $35~\mathrm{kcal~mol^{-1}}$. This has well-known stereochemical consequences in that amines ...
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Why don't trigonal S and P compounds undergo inversion at room temperature?
Most molecules containing nitrogen atoms in trigonal pyramid configuration undergo a relatively fast process of inversion at room temperature. On the other hand, the free energy barrier for phosphines,...
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Molecular chirality and optical rotation
Why does having molecular chirality result in optical rotation? The dissymetry or chirality of molecules translates to the rotation of plane polarized light, the magnitude and direction depending on ...
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What are known examples of drugs that racemize/stereoconvert in vivo, and how are they converted?
It is known that although only the (S)-enantiomer of the infamous sedative thalidomide possesses teratogenic properties, it is not very useful to administer the pure (R)-enantiomer since it is ...
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What are the CIP rules for cyclic substituents?
Here's what I read on Wikipedia (section "Cycles"):
To handle a molecule containing one or more cycles, one must first expand it into a tree (called a hierarchical digraph by the authors) by ...
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Can geometrical isomers be enantiomers?
I have just been pondering upon the question above. I have found this example and I am sure they are enantiomers, but do they also count as geometrical isomers?
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How do I determine the absolute configuration experimentally?
Let's say I synthesized or isolated a chiral molecule and want to know the absolute configuration (R or S) of that molecule. I could obviously solve the structure by X-Ray crystallography, but that's ...
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Why six C atoms are usually seen in cyclic compounds?
When it gets to Carbon-based molecules, one very possible structure when there are more than six C atoms is the hexagon; though not mostly perfect, it emphasizes that six Carbon atoms tend to bond ...
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Number of diastereomer pairs of 1,3-dichloro-1,2,3-triphenylpropane
How can I determine the number of possible pairs of diastereomers here?
My first guess was two: RR with RS and SS with RS. But what about the potential chirality center middle carbon? There are two ...
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IUPAC name for 1,2,3-trichlorocyclopropane?
What is the IUPAC name for the two isomers of 1,2,3-trichlorocyclopropane? Similarly what is the name for isomers of 1,2,3,4-tetrachlorocyclobutane, 1,2,3,4,5-pentachlorocyclopentane, etc?
1,2,3-...
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What's the difference between alpha-glucose and beta-glucose?
What's the difference between $\alpha$-D-glucose and $\beta$-D-glucose? Are they isomers? Or do they differ in their elemental composition?
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Chirality of substituted adamantanes
Is this compound chiral?
I can't tell where the chiral centres are because this polycyclic backbone is too confusing. I tried to draw a mirror image, but I got really confused and couldn't tell ...
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Number of stereoisomers of tetramethylspirononane
The above compound – 2,3,7,8-tetramethylspiro[4.4]nonane – clearly exhibits both optical and geometrical isomerism. The question is, how many stereoisomers does it have in all?
As the number of ...
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Atropisomerism of naphthyl alcohol
In March's Advanced Organic Chemistry (6th ed.), it's stated that the above two are atropisomers. I don't get why is it so. How is the topmost $\ce{C}$ locked in its place? Surely, there's steric ...
user58382
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Is circularly polarized light ever used to isolate particular chiralities?
Chiral molecules tend to absorb one circular polarization of light more than the other. Is this ever used to isolate a particular enantiomer?
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How are non-carbon stereogenic centers named (S/R)?
The R/S naming system for stereocenters relies on the Cahn–Ingold–Prelog priority rules to rank the four substituents of a stereocenter; the R or S name is then attributed depending on the spatial ...
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Neighbouring group participation with and without retention of configuration in nucleophilic substitution of 2,6-dichloro-9-thiabicyclo[3.3.1]nonane
Treatment of the dichloride A under the conditions indicated gives B with retention of configuration, while treatment of dichloride C gives D with inversion of configuration.
I am having difficulty ...
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Dihedral angle of gaseous and crystalline HOOH
Why does hydrogen peroxide exhibit a dihedral angle of $111.5^\circ$ in the gaseous state? And a dihedral angle of $90.2^\circ$ in the crystalline phase?
I know that in general, there is likely to be ...
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Mismatch of plane of symmetry vs Gold Book's definition for a pseudochiral carbon
Here is pentane-2,3,4-triol:
At first glance, without deciding the configurations at each chiral carbon, we can clearly see that this molecule has a plane of symmetry, perpendicular to the plane of ...
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Utility of Bent's Rule - What can Bent's rule explain that other qualitative considerations cannot?
Does Bent's rule have any utility? I got a vehement earful for "NO." Points raised by my professor:
Coulombic considerations can be used to rationalize bond angles, strengths, and lengths without ...
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Molecular knots absolute configuration
How is the absolute configuration of chiral molecular knots determined? What rules should be applied? For centrochiral compounds, the CIP rules are applied, for axially chiral is described here and ...
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Boiling and melting point of trans- and cis-but-2-ene
The boiling point of trans-but-2-ene is lower than that of its cis isomer but the melting point of the former is higher than the later. Why is it not following the same order? Is there any factor of ...
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Configuration of chiral center in cocaine
I couldn't get the absolute configuration for the chiral center I marked. I got R, but according to my answer key it is apparently S. Would really appreciate an explanation.
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Effect of enatiomers in pharmaceuticals [closed]
Often (or always?) one enantiomer of a certain drug will be effective and the other ineffective or harmful. The famous example is thalidomide, where one enantiomer caused mutilation of the unborn ...
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What are the criteria for a molecule to be chiral?
What are the criteria for a molecule to be chiral?
(We frequently get questions of this type, so this is an attempt to construct a suitable general answer for duping.)
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Maximum observed optical rotation through a polarimeter
Is there a maximum optical rotation of plane polarized light that can be observed using a polarimeter?
I understand that in a polarimeter, light passes through a filter that converts it into plane ...
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How is the Felkin-Anh model of stereoinduction correctly explained with MO theory?
One method to predict stereoinduction in asymmetric reactions is the Felkin-Anh model (derived from the more basic Cram model) that applies to nucleophile attacks on α-chiral aldehydes. In a ...
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Do molecules with axial chirality have "stereogenic units"?
This question is a follow-up to a recent question on discodermolide stereochemistry that I answered here. In the course of reading IUPAC's definition of "stereogenic center", I wondered if axially ...
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Does a chiral centre have to have 3 or 4 different groups attached?
I am seeing conflicting answers on the net
e.g.
A carbon atom is chiral if it has four different items bonded to it at the same position. (Wiki)
compared to
Stereocenter (chiral center): An ...
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Difference between Epimers and Diastereomers
My lecture notes describe epimers as compounds which differ by
configuration at only one carbon and gives the example of D-erythrose and D-threose as being epimers.
However isn't that the same thing ...
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Is phosphorus a stereogenic centre in this phosphate ester?
My textbook says that in the above diagram that there is only 2 stereoisomers. I am guessing this is due to the stereogenic carbon atom and not due to the phosphorus atom which apparently isn't a ...
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R/S configuration of bridging carbon in bicyclic system
I am trying to figure out the R and S configuration of bridging carbons in bicyclic systems.
In the image, there are two bicyclic systems and depending on the position of the Br substituent, the R or ...
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Can you have a meta stereocenter?
Imagine a compound such as 1,3-dibromo-1,2,3-trichloropropane. Since the first and third carbons are attached to four different groups, they are both chiral centers. Assuming that both of these ...
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How is exact racemization possible? [closed]
A racemate consists of 50 % $d$ and 50 % $l$ forms of an optically active compound. But how can someone ensure exact 50% quantity comparing molecule by molecule? There will always be some difference ...
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Which biphenyl is optically active?
Which biphenyl is optically active?
I know that it can never be 1. I don't think it will be 4 either as I read that it should be ortho-substituted biphenyl.
So, when I look at 2 and 3, I can't make ...
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Is it possible, chemically, to change a dextrorotatory compound to its levorotatory counterpart?
Is it possible, chemically, to change a dextrorotatory compound to its levorotatory counterpart? E.g., is it possible to change dextrodopa to levodopa?
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Sulfinate R/S configuration
How to determine the configuration of the attached chiral compound? It can be represented with two Lewis structures, in the one to the left, the =O substituent has the biggest priority, while in the ...
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Total number of stereoisomers of cyclobutane-1,2,3,4-tetracarboxylic acid
Question
Find all stereoisomers of:
My attempt
I got four isomers, and none of them seem to be optically active as they either have a plane of symmetry or a point of symmetry:
However, my sir keeps ...
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