37
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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 ...
- 71.1k
31
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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
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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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27
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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, ...
- 8,465
23
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How can a molecule with a double bond on one side have a plane of symmetry, and thus, be achiral?
I think this is a case of picture being worth a thousand words. Arguably the easiest way to visualize the plane of symmetry for nonbornene (mirror plane m) is to redraw the molecule in 2D:
...
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21
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 ...
- 71.1k
19
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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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18
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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
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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 ...
- 11.6k
17
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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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17
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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 ...
- 17.3k
16
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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 ...
- 43.8k
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 ...
- 12k
14
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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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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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14
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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 ...
- 16.4k
14
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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
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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 ...
- 71.1k
13
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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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13
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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-...
- 16.4k
13
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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 ...
- 633
12
votes
How to derive these general formulae for number of stereoisomers of a compound with a possible plane of symmetry?
I managed to crack the formula for optical isomers with odd chiral centers, so I'll share my attempt here. Hopefully others may innovate on it and post solutions for other formulae.
Pseudo-chiral ...
- 9,688
12
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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)(...
- 23.9k
12
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Can geometrical isomers be enantiomers?
Technically, this double bond should not be labelled as (E)- or (Z)-.
It is what is known as an enantiomorphic double bond, for which the proper stereodescriptors are seqCis and seqTrans. This is ...
- 71.1k
11
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Is (2R,3S)-butane-2,3-diol chiral?
The staggered, conformation of (2R,3S)-butane-2,3-diol (1a) that you have shown does not have mirror planes but rather a center of symmetry, which is the reason that this conformation does not rotate ...
- 16.4k
11
votes
Can heteroatoms with lone pairs be chiral centres?
Two cases are possible:
The nitrogen case with inversion frequently happening. Here, the compounds inverts via a planar transition state going from $\mathrm{sp^3}$ hybridisation to $\mathrm{sp^2+p}$ ...
- 67.3k
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 ...
- 67.3k
11
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Why is the name 'propylene oxide' preferred for epoxypropane?
why is 'propylene oxide' the preferred name for epoxypropane?
Propylene oxide is not the "preferred" IUPAC name (PIN): Wikipedia lists the PIN as 2-methyloxirane, which is in line with the 2013 IUPAC ...
- 71.1k
11
votes
Do isotopic groups cause optical activity?
From a 2007 paper::
Here we show that instrumental advances in Raman optical activity, combined with quantum chemical computations, make it possible to determine the absolute configuration of (R)-[$...
- 21.8k
11
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Does 1,4-dimethylcyclohexane have a chiral center?
As it is said in the definition of IUPAC, for a carbon atom to be chiral it should be attached to 4 different groups:
In case of 1,4-dimethylcyclohexane, you will see that the two groups on the right ...
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