Questions tagged [chirality]

Applicable to questions about the ability of a molecule (or class of molecules) to be superimposed on their mirror image(s).

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19
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2answers
6k views

What is the perfect definition for chirality?

Why is chirality defined differently for organic and inorganic compounds? Why are inorganic compounds deemed to be optically active if they have more than one of the same ligands attached to the ...
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1answer
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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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3answers
8k views

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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3answers
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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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3answers
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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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3answers
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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 this compound. C-4 of the cyclohexane ring has two groups with exactly the same connectivity, and the exocyclic double bond can't give ...
23
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3answers
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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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3answers
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Is (2R,3S)-butane-2,3-diol chiral?

Is the attached compound a chiral or achiral overall? My lecturer said that this is an achiral compound because it has a superposable mirror image but I don't get that. So I tried to figure out the ...
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1answer
332 views

Twisting stereoisomers with rings to determine R/S [closed]

I know that if the smallest atomic number group is not in the back, we can twist the molecule so that it is in the back and then determine if it is R/S (Left image). But if the chiral center is ...
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3answers
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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 ...
25
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1answer
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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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2answers
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Chirality of heteroatoms [duplicate]

Why is a phosphorus atom with three different substituents chiral, but nitrogen isn't? Nitrogen inverts fast, while phosphorus obviously much slower. How is that explained?
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4answers
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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 ...
14
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1answer
1k views

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 ...
11
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1answer
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Are there chiral compounds that don't rotate plane-polarized light?

I know that meso compounds have chiral centers but don't rotate plane-polarized light, and I know that there can be non-traditionally chiral compounds (e.g. ones with large substituents that prohibit ...
11
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2answers
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Are all higher cycloalkenes chiral?

Are all higher trans-cycloalkenes chiral as trans-cyclooctene is? This question supplements my previous question: Why is trans-cyclooctene chiral? See also the follow-on question: Do more double ...
21
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2answers
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Is there a simple way to get the circular dichroism of a molecule from its structure?

Are there any heuristics to get the relative absorbtion of left and right circularly polarized light by a molecule from its molecular structure? Is it even possible to predict which polarization is ...
8
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2answers
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Why do only chiral molecules rotate the plane of polarized light and how do they rotate it?

I have learnt that only chiral or unsymmetrical molecules can rotate the plane of linearly polarized light. But, why is it so? And how can molecules rotate the plane or what does it actually mean by ...
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2answers
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Does an axis of symmetry determine chiralty?

What I've understood about chirality and elements of symmetry: A molecule that is not superposable on its mirror image is said to be chiral. Plane of symmetry: An imaginary plane cutting a compound ...
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2answers
556 views

Link between centrosymmetry, dipole moment and chirality

What is the relationship between the three concepts in the title? I know all centrosymmetric molecules are achiral, but not all achiral molecules are centrosymmetric. Thus, there are no molecules ...
4
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2answers
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Dependence of the angle of rotation on the wavelength of plane polarized light

Wavelength difference is a big deal, I know. It can solely change the whole interaction between the chiral molecule & the light. But I am not sure what's the mechanism by which light of different ...
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2answers
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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 ...
13
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1answer
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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 ...
11
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1answer
665 views

Which alkene has a higher Cahn-Ingold-Prelog priority in (2Z,5E)-hepta-2,5-dien-4-ol?

How do I determine whether the central carbon of this compound is (R) or (S)? On both the sides of carbon, the groups are same. They differ only in the relative position of hydrogen atoms. On what ...
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1answer
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What causes rapid nitrogen inversion?

When I asked my teacher whether a nitrogen bonded to 3 unique groups counted as a chiral center, they said that it did not because nitrogen undergoes rapid inversion at room temperature. What causes ...
15
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1answer
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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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3answers
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Concept of "non-superimposable mirror image" in chirality

I didn't understand the fact that chiral objects are non-superimposable on their mirror images. I mean, if you put your right hand (apparently an achiral object) in front of a mirror, the mirror image ...
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1answer
875 views

Example of an achiral molecule without a plane of symmetry or inversion center?

Some websites, such as this textbook, mention how generally a plane of symmetry or inversion center in a molecule is enough to consider it achiral. Nonetheless, this source clarifies but if these ...
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1answer
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M/P nomenclature for axial-chirality

Synthesis and Chiral Resolution of C3-Symmetric Tribenzotriquinacenes, Eur. J. Org. Chem. 2016, Early View article DOI: 10.1002/ejoc.201600890 I came across this graphical abstract with M and P ...
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2answers
936 views

Do more double bonds cause a bigger number of stereoisomers in cycloalkenes?

If trans double bonds cause cycloalkenes to be chiral, does a second trans or maybe cis double bond induce another chiral plane and hence four stereoisomers are possible for the given cyclodiene? The ...
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1answer
999 views

How to find the number of stereoisomers of a tetra-substituted allenes, exhibiting both axial and central chirality?

I need a reliable method for determining the number of diastereomers and enantiomeric pairs of the following series of compounds bearing in mind that the substituent groups A are chiral on their own (...
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1answer
305 views

What kind of optical activity requires chirality?

From "Meso compound" in Wikipedia: A meso compound or meso isomer is a non-optically active member of a set of stereoisomers, at least two of which are optically active. This means that despite ...
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1answer
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Do L-sugars (enantiomers of natural sugars) have a sweet taste?

I'm wondering about how L-sugars taste. They are obviously not digestible by humans, but what do they taste like? If they are sweet, too, why isn't sucrose with the unnatural chirality used as a zero-...
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3answers
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Axial or planar chirality in spiro[3.3]hepta-1,5-diene

The two spirocyclic compounds drawn below are enantiomers. My question is, do they exhibit axial or planar chirality? 3D representations:
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1answer
246 views

Use of axis of symmetry

Does an axis of symmetry determine chiralty? Is axis of symmetry considered a true symmetry? From the above two links, I read that a compound having axis /alternating axis of symmetry is NOT ...
6
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2answers
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What do the stereochemical labels D and − mean in tartaric acid?

Why is the isomer of tartaric acid above labelled as ᴅ and (−)? it rotates plane-polarized light clockwise it rotates plane-polarized light anticlockwise it is an equimolar mixture of the ...
5
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1answer
661 views

Is the product of Lindlar hydrogenation of (2Z,4S)-4-methylhept-2-en-5-yne optically active?

According to me the poisoned catalyst will only reduce the triple bond so the compound produced must be optically active.. But the answer given is that the final product is optically inactive.. is it ...
3
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1answer
902 views

Racemization of biphenyl compounds

How does the effect of heat and effect of substituents affect racemization of biphenyl compounds?
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6answers
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Chirality of symmetrically substituted biphenyl

I am facing trouble with the following problem: is 2,6-dimethyl-2',6'-dinitro-1,1'-biphenyl chiral? My idea is that there is a axis of symmetry along the line joining the two benzene molecules. Hence ...
13
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1answer
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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 ...
13
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1answer
967 views

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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3answers
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Is rotation of a mirror image allowed in order to determine chirality? Doesn't rotation alter the mirror image of the molecule?

So, chiral molecules are those which have non-superposable mirror images. trans-1,2-Dimethylcyclopentane is chiral; 2-butanol is chiral; both don't superpose on their mirror image. Then my book ...
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3answers
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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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1answer
721 views

Simple experiments involving enantiomer synthesis

I want to do an experiment to investigate factors affecting the synthesis of chiral molecules. The only problem is, my institution doesn't have much money, and it seems like the chemicals required for ...
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4answers
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Are our hands really chiral?

Everyone says that our left and right hand are mirror images of each other and are non-superimposable, unlike a sphere whose mirror image is exactly superimposable. But shouldn't our left and right ...
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2answers
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Is 2-bromobutane chiral?

My textbook says 2-bromobutane is chiral, but it look like it will form superimposition mirror image
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1answer
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Determining chirality after considering conformational interconversion in a cyclohexane

Basically I want to know what does the question mean when it says "taking into consideration conformational interconversions." I assume it means, when I draw the mirror image of the given compound, ...
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0answers
291 views

Is methyl phenyl sulfoxide optically active? [duplicate]

I am concerned about the stereogenic centres. But in this compound there is no chiral centres present. Sulphur is $\mathrm{sp^2}$-hybridized, so it cannot be chiral anyway. But I can see there is no ...
2
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4answers
502 views

Gas phase chiral molecules

Are there any molecules that are chiral that are also gases at room temperature? Failing that, what chiral molecules have a high vapor pressure? Propylene oxide has a boiling point of only 34 C, so ...
7
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1answer
982 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 ...