35 votes
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Why is 1-ethylidene-4-methylcyclohexane chiral?

The strict criterion for a compound to display chirality is that it must not be superimposable upon its mirror image. Let's ignore the chair conformation of the ring for a while, and assume it adopts ...
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30 votes
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What is the perfect definition for chirality?

The correct definition of chirality is given in the IUPAC gold book as follows: chirality The geometric property of a rigid object (or spatial arrangement of points or atoms) of being non-...
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27 votes

What is the perfect definition for chirality?

I think Martin has provided an excellent answer, and I would like to supplement it with a few additional details and examples that might prove insightful. So as I already mentioned in the comments, ...
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26 votes
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Why is trans-cyclooctene chiral?

Very interesting question! The key word you are looking for is planar chirality. In trans-cyclooctene, the polymethylene bridge can either go "in front of" or go "behind" the plane of the double bond, ...
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26 votes
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Can heteroatoms with lone pairs be chiral centres?

Generally, amine nitrogens will not behave like a normal asymmetric carbon. Simple amines are roughly $\mathrm{sp^3}$ hybridiized and the molecules you use as examples do have 4 (we include the lone ...
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20 votes
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Chirality of substituted adamantanes

Yes, this compound is chiral. The polycyclic backbone is called adamantane. It has $T_\mathrm{d}$ symmetry, meaning that as far as chirality goes, it behaves like a perfect tetrahedron, somewhat like ...
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18 votes

Are our hands really chiral?

Holding your hands in this way merely proves that your hands are mirror images. If you take any object (chiral or not) and hold it up to a mirror, you can always align common features. Imagine ...
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18 votes
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Why do Enantiomers have different chemical properties with optically active reagents?

I think a simplified version of the enzyme example is helpful here. Consider this image of binding a molecule to a receptor: Using a model of enantiomers where the attached groups are just ...
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17 votes
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Are there chiral compounds that don't rotate plane-polarized light?

Good question. There's a phenomenon named cryptochirality[1] (meaning “hidden chirality”), when a compound, though chiral, has practically unmeasurable optical rotation activity. It can happen to ...
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16 votes
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Chirality of symmetrically substituted biphenyl

No, the biphenyl above is not chiral. 2,2′,6,6′-tetrasubstituted biphenyls are nonplanar at room temperature in order to avoid steric clashes between the substituents. This can in general give rise to ...
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16 votes

Are our hands really chiral?

But if i rotate my left hand by 180 degrees ie now palm of my left hand faces away from me then both the left and right hand are superimposable . Turning your hands this way only makes them ...
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15 votes
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Is there a simple way to get the circular dichroism of a molecule from its structure?

Is there a simple way to get the circular dichroism of a molecule from it's structure? Short Answer: Yes, for many molecules if you know the molecule's structure, then you can predict the shape of ...
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15 votes
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Is 2-bromobutane chiral?

For a molecule to be chiral it must have non-superimposable mirror images. Here is a drawing of the two mirror images for 2-bromobutane. The chiral carbon atom is denoted by an asterisk. In the ...
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15 votes
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Are all higher cycloalkenes chiral?

Background One can draw conformations of n-butane with the carbon-carbon bonds oriented in certain directions and the methyl hydrogens pointing in certain directions that are chiral. However, since ...
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15 votes

Chirality of symmetrically substituted biphenyl

Yes, the molecule should exhibit chirality, but this can likely only be observed below room temperature. In the optimised1 molecular configuration the molecule cannot be superimposed on its mirror ...
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15 votes

Are there reactions where the stirring direction would make a difference?

No, for three reasons: Firstly, you need a relatively large molecule and/or a high viscosity and/or a strong shear/extensional flow, before the molecule even notices that it´s in a nonuniform ...
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14 votes
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What are the criteria for a molecule to be chiral?

Mirror images The very first definition of a chiral molecule is one where it is not superimposable on its mirror image. Therefore, one of the most straightforward ways to determine chirality is to ...
13 votes
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Why is the inversion barrier larger in PH3 than it is in NH3?

Ammonia is the classic system for $\ce{sp^3}$ hybridisation save methane. The lone pair (and each of the $\unicode[Times]{x3C3}$-bonds) has almost $25~\%$ s-character which corresponds nicely to $\ce{...
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13 votes

What causes rapid nitrogen inversion?

In the second row of the periodic table, elements have relatively small differences between the size their $\mathrm s$- and $\mathrm p$-orbitals. Therefore, the orbitals of $\ce{NR3}$ can go from $\...
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13 votes

Why is 1-ethylidene-4-methylcyclohexane chiral?

This question has been answered in elegant fashion by @orthocresol. I'd like to expand the discussion somewhat by detailing how digraphs and Cahn-Ingold-Prelog-(Helmchen) rules account for the ZR and ...
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13 votes

How is plane polarized light rotated by chiral compounds?

Circularly polarized light is like a helix that twists through space. The two components are mirror images of each other. Now, every molecule interacts with both the left-handed twisting light and the ...
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12 votes
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Maximum observed optical rotation through a polarimeter

This is something I discovered after an attempt at a more mathematically rigorous investigation of how to interpret polarimetry results. It's not that hard, but I don't think you'll ever find a ...
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12 votes

Why is the inversion barrier larger in PH3 than it is in NH3?

Disclaimer: This answer neglects quantum tunnelling effects, which are significant in such compounds. The gist of it is that because nitrogen is smaller and lighter than phosphorus, the rate of ...
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12 votes

Configuration of chiral center in cocaine

You are actually right, that stereocenter does have R stereochemistry. The four substituents to the chiral center in question are: 1 - $\ce{CO(O)}$ = $\ce{C(O)3}$ 2 - $\ce{C(O)(C)(H)}$ 3 - $\ce{C(N)(...
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12 votes
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Can geometrical isomers be enantiomers?

The enantiomers 1a and 1b can have their double bonds defined by CIP rules 1a and 5. Rule 1a dictates that CH3>H while Rule 5 has R>S. Thus, 1a has an E-double bond and 1b is of the Z-configuration ...
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11 votes

How to identify a compound as chiral or achiral

Look for carbons with four different groups attached to identify potential chiral centers. Draw your molecule with wedges and dashes and then draw a mirror image of the molecule. If the molecule in ...
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11 votes

Chirality of symmetrically substituted biphenyl

The simplified point of view in a way that students should be expected to answer the question It is not the axis of symmetry (which is a $C_2$ axis in this case) that is important but rather that the ...
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11 votes
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Mismatch of plane of symmetry vs Gold Book's definition for a pseudochiral carbon

The Gold Book definition for a meso compound is the achiral member(s) of a set of diastereoisomers which also includes one or more chiral members. So, a meso compound has chiral subsets. Here ...
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