# Tag Info

## Hot answers tagged symmetry

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### What is the mathematical basis behind the Jahn-Teller effect?

1. Perturbations As already mentioned, the Jahn–Teller effect has its roots in group theory. The essence of the argument is that the energy of the compound is stabilised upon distortion to a lower-...
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### Does trans-decalin really have a plane of symmetry?

It's not easy to see from a diagram, because it distorts bonds and angles. I recommend building it with a balls-and-sticks model set. You can also use a molecular viewer to model it; there are a ...
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### Theoretical basis behind orbital correlation diagram for pericyclic reactions

Introduction Instead of the usual cycloadditions (which has some extra complications in terms of the reacting orbitals), let's consider the concerted reaction $\ce{H2 + D2 -> 2HD}$. We'll come ...
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### Why is 2-methyl-2,3-pentadiene achiral (allene)?

I'll start by linking to Symmetry @ Otterbein, as it's a very useful tool for looking at various structures and seeing planes an axes of symmetry. If you're having issues visualising rotations and ...
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### Relationship between the symmetry number of a molecule as used in rotational spectroscopy and point group

This is not in general true Consider molecules a point group not containing inversion symmetry, e.g. $C_2$ hydrogen peroxide The $C_2$ group has only two elements, $E$ and $C_2$, and the $C_2$ ...
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### How are there two C3 rotation axes in ammonia?

In a character table for $C_{3v}$, $2C_3$, means that the element is actually 2 $C_3$ elements in the same conjugacy class. That means the two $C_3$ operations are related in some way. In fact, it ...
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### What constraints are imposed on a wavefunction by the symmetry of the system?

I use quantum chemistry about as much as a lumberjack uses math (that is, just enough not to fell a tree on one's own head), so my answer will be short and hopefully useful as a tl;dr to someone else'...
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### How do I show that a transition is magnetic dipole allowed with group theory/symmetry?

For a state-to-state transition coupled by an operator to be allowed, the direct product of the irreducible representations (irreps) of all three components must contain the completely symmetric irrep ...
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### How are there two C3 rotation axes in ammonia?

The top row of the character table does not refer to symmetry elements, but rather symmetry operations. (For the difference between the two, see Wikipedia:Molecular symmetry.) In this particular case, ...
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### Derivation of the Orgel diagram for octahedral d2 complexes

1. Weak-field and strong-field limits I will adopt the description used in Figgis and Hitchman's Ligand Field Theory and Its Applications (p 5), because I cannot really phrase it better: It is ...
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### How do I find the ground state term symbol for transition metal complexes?

To find the ground state term symbol, you should be using symmetry and group theory arguments, you shouldn't have to resort to searching Tanabe-Sugano diagrams to get the answer. We'll start with ...
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### Is there a physical explanation why benzene's pi molecular orbitals in a Frost circle are degenerate but pyridine's are not?

My first thoughts are along the lines of your second-last paragraph. Here is a quick sketch of how to formalise it. From simple Hückel theory, you can obtain the coefficients of the AOs in the MOs: ...
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### Does 1,3-dichloroallene possess a C2 symmetry axis?

A $C_2$ axis is indeed here—although not the one that you are thinking of: your suggestion of a $C_4$ then $C_2$ rotation does not qualify as a $C_2$ symmetry operation. There is a true $C_2$ axis ...
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### AB5E type molecule

Why? Because there is no other choice. Starting from the AB6 octahedral configuration, all six vertices of the octahedron are symmetric, so it doesn't matter whichever one you “choose” to replace by ...
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### Why doesn't 1,3-dichloro-2,4-dimethylcyclobutane have a plane of symmetry?

Ivan already stated quite briefly in the comments, that the planes you drew would transform an upward facing chlorine to a downward facing chlorine and vice versa, and that the same holds for the ...
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### Rule of mutual exclusion: is the converse true?

Have a look at the point groups O (not $\ce{O_h}$) I, $\ce{D_{5h} and C_{5h}}$. A pic of an O point group molecule is shown below. The $\ce{c_2}$ axes are not shown. Taken from molecule-viewer.com web ...
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### Rule of mutual exclusion: is the converse true?

If there is a molecule of $O$ (as opposed to $O_h$) or $I$ (as opposed to $I_h$) symmetry, it would be such a counter example (no mode that is both IR and raman active, and not centrosymmetric). ...
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### Why does the 31P{1H} NMR spectrum of cis-[Mo(CO)2(dppe)2] show two signals?

In this complex there are two different 31P environments which are not related by symmetry: The two green phosphorus nuclei can be interconverted by a $C_2$ rotation (the rotation axis bisects the OC–...
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### Example of an achiral molecule without a plane of symmetry or inversion center?

Part 1 Are there any molecules lacking plane of symmetry/center of inversion but that are achiral due to presence of an axis of improper rotation? Yes, although such examples are very rare. In ...
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### How are these molecules chiral and achiral?

Regarding the first molecule: I understand that the simplistic Fischer projection - with all its bond depicted by solid lines - can be very confusing at first glance in determining optical activity. ...
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