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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-superposable on its mirror image; such an object has no symmetry elements of the second kind (a mirror plane, σ = S1, a centre of inversion, i = S2, a rotation-...


24

Asked and answered, but I think one thing that's missing is that allenes are not planar like alkenes or alkynes are. You can refer to this question for an explanation. The dihedral angle between the two halogens is 90 degrees (ideally). Here's an animation hopefully providing a better view of the 3D structure: This results in the two mirror images being ...


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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, the definition of chirality is rooted in symmetry. A chiral compound can contain no improper axis of rotation ($S_n$), which includes planes of symmetry ($S_1 = \...


23

since for every orientation of the molecule, we can reverse the orientation such that the light appears to be falling on the molecule from a direction other than the one for our original molecule. This is false. Let's take 2-butanol. For this stereoisomer, light is turning clockwise when viewed from the right side (I'm not sure of this, but we can assume). ...


23

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 pair of electrons as a substituent) different substituents around the central nitrogen atom. So in principle me might consider it asymmetric or chiral. But ...


22

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, assuming you fix the double bond and the two hydrogens in place. As pointed out by @jerepierre, they are considered different molecules due to a high-energy ...


19

Achiral cyclic compounds like 1,2,3-trichlorocyclopropane may contain pseudoasymmetric centers. Pseudoasymmetric centers have distinguishable ligands (“a”, “b”, “c”, “d”), two of which are nonsuperposable mirror images of each other (enantiomorphic). The lower case stereodescriptors “r” and “s” are used to designate the absolute configuration of ...


19

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 a planar conformation. You could draw a side-on view of the ring like this: Its mirror image would look like this. This is an example of axial chirality (...


18

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 methane does. It also has the interesting property that if you extend the C-F, C-Cl, ... bonds inwards, they will all meet at the same point. Those red dotted ...


17

Chirality is a property of objects in which they lack certain symmetry operations, specifically improper rotations, including the mirror plane and inversion operations. For example, 3-dimensional chiral objects lack mirror symmetry. According to Wikipedia: The feature that is most often the cause of chirality in molecules is the presence of an asymmetric ...


17

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 instead placing one of your hands inside the other. You may be able to align the overall thumbs and fingers, but they will be facing opposite directions, thus are not ...


16

I assume it's deuterium, the isotope of hydrogen that has a single neutron as well as a proton in the nucleus. As such, it has the same atomic number as hydrogen, which means you break the tie on atomic mass -- deuterium is higher priority than hydrogen but lower than everything else.


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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 superimposable if you make the assumption that they are two-dimensional objects, where the normal vectors coming out of both sides of a given hand are indistinguishable. ...


14

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 rotation about single bonds is typically fast at room temperature, these chiral conformers of n-butane would only be resolvable at extremely low temperatures. ...


13

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 the optical rotary dispersion (ORD) or circular dichroism (CD) curve. Conversely, and perhaps more importantly, if you know the shape of the ORD or CD curve, ...


12

Yes. For some chiral compounds, each enantiomer in a racemic mixture absorbs certain frequencies of light differently depending on the circular polarization type of the light. That means that if you can pump in sufficiently intense and energetic (e.g. ultraviolet) circular polarized light pulses into the racemic mix of such compounds, you may in some cases ...


12

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 - $\ce{C(N)(C)(H)}$ 4 - $\ce{H}$ These are ranked and numbered according to the Cahn-Ingold-Prelog priority rules. Adding the numbering to the structure: Orienting the ...


12

Yes, the molecule should exhibit chirality below room temperature. In the optimised1 molecular configuration the molecule cannot be superimposed on its mirror image. This is because of the out-of-plane rotation of the nitro groups. The thermodynamic most favourable structure is of $C_2$ symmetry and has no mirror plane (see above). Contrary to the ...


12

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 molecules with chiral center(s) bearing very similar substituents. (So, no tricks with bonded slightly modified enantiomeric pairs are needed.) An example is 5-...


11

In your example, the stereodescriptors R and S are already given. The remaining question is about the double bond which gives rise to cis-trans isomerism. In the hierarchical Sequence Rules, we finally find P-92.1.3.5 Sequence Rule 5 An atom or group with descriptor ‘R’, ‘M’, and ‘seqCis’ has priority over its enantiomorph ‘S’, ‘P’ or ‘seq Trans’. ...


11

Ortho-Ortho-tetrasubstituted biphenyls become non-planar at room temperature in order to have minimum electronic repulsion among substituents.In this orientation(phenyl planes perpendicular to each other) the free rotation of C-C single bond is restricted and molecule shows optical activity due to molecular disymmetry. Actually looks like this: The two ...


10

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 the mirror image is the same molecule, it is achiral. If they are different molecules, then it is chiral. Here you're particularly interested in the C in the CH....


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In the second row of the periodic table, elements have relatively small differences between the size their s- and p-orbitals. Therefore, the orbitals of $\ce{NR3}$ can go from $sp^3$ to $sp^2$ with relatively little energy increase, so an amine can become planar and then reorient with the inverted stereochemistry. The same occurs with carbanions. I'm not ...


10

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 plane polarized light. There are two other stable, staggered conformations of the diol, namely 1b and 1c. They are a racemic pair, each of which is chiral. But ...


10

When no bond from the chiral center has up or down graphical indication, it can mean any or unknown stereochemical configuration. Which might be confusing, because it can also mean, that the stereochemical configuration on this atom was mistakenly omitted. To explicitly indicate that any or unknown configuration, wavy line bond can be used: (Hydrogen atom ...


9

Let's see if a picture can help. Newman projections can be handy in analyzing the stereochemistry of allenes. On the left is a Newman projection of methyl allene (buta-1,2-diene). There is a sigma plane of symmetry that is perpendicular to the screen and contains the 3 allenic carbons plus the methyl group. Any molecule with a plane of symmetry is ...


9

Your hands are chiral, that is why you need two different leather gloves, one that only fits your right hand, and one that only fits your left hand. If your hands were superimposable, then you would only need one kind of glove and it would fit both hands.


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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 similar analysis in a book because in practice the details are pretty much unnecessary for experimental purposes (though fun mathematically!). Before we begin, it's ...


9

In order to arrive at an unambiguous description of stereoisomers, the priority for the groups attached to the chirality center is established by the application of ‘Sequence Rules’. In the hierarchical Sequence Rules given in Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), we find P-92.1.3.3 Sequence Rule 3 ...


9

I consider the concept of prochirality as a property of an achiral compound (or centre), that can be turned into a chiral compound (or centre) in one step (proprochiral: in two steps) by means of substituting or addition. Hence all carbon centres with three different ligands (substituents or hydrogen) can be considered prochiral. Prochirality is ...


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