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Questions tagged [symmetry]

The description of the symmetry present in molecules. Molecular symmetry is useful for explaining or predicting of a molecule's chemical properties.

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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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When is it true that more nodes equals higher energy?

Consider all the MOs of some isolated molecule. (It could be a single atom too; I'll use MO to refer to AOs as well.) Number them in increasing order of the number of nodes (node = surface where the ...
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How can I find the symmetry labels of atomic orbitals in a molecule?

What are the symmetry labels for the p and d orbitals of platinum in $\ce{[PtCl4]^2-}$? I understand how to find the point group of a molecule, but am not sure how to use the character table to find ...
Kinformationist's user avatar
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How do I find the ground state term symbol for transition metal complexes?

I have a problem where I'm trying to match metal complexes with the proper ground state term symbol. I've tried doing a Google search and looking for a process, but haven't had any luck. I decided ...
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Theoretical basis behind orbital correlation diagram for pericyclic reactions

When discussing pericyclic reactions, the Woodward-Hoffman rules allow one to predict whether a reaction will be thermally/photochemically allowed. This has been discussed in many questions on chem.SE,...
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What constraints are imposed on a wavefunction by the symmetry of the system?

As a follow-up to my answer here, I'd like to ask what exactly does it mean for a wavefunction to "respect the symmetry" of the system. The original context is: immediately after ionisation of $\ce{...
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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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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 ...
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What are t2g and eg in CFT?

In the crystal field theory (CFT), when the splitting of the d-orbital occurs, it gets divided into two parts. The upper part with higher energy is the $\mathrm{e_g}$ and the lower part with lower ...
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What is the mathematical basis behind the Jahn-Teller effect?

Both first-order and second-order Jahn-Teller distortions play a very important role in chemistry. It is often said that the Jahn-Teller effect is based on symmetry arguments, and hence nothing can ...
orthocresol's user avatar
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How does one recognized Td/Oh symmetry in molecules?

The identification of point groups of a molecule is usually done following a strict scheme, either manually or algorithmically. In all textbooks I could find, however, the first step of the scheme is ...
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How do I show that a transition is electric dipole allowed with group theory/symmetry?

This is actually a follow up of this question The follow-up is not because of the electric instead of magnetic dipole (this is trivial). It is because I'm interested in extra info. Suppose I have a ...
Davide Sangalli's user avatar
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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 ...
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For two compounds that are symmetrical, why does the more compact one have a higher melting point?

In this post, I refer to two molecules B (Di-tert-butyl ether) and C (Dibutyl ether). Wikipedia: Di-tert-butyl ether (B) b.p. 107.2 C m.p. - 61 C ...
ning's user avatar
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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 ...
Eliot Behr's user avatar
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Conventional unit cell for a hexagonal crystal system

The figure shows a unit cell of a hexagonal crystal system. Drawn in bold, is the unit cell. The lightly shaded one is a unit cell as well and has a six fold symmetry along an axis, hence is more ...
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Jahn-Teller Distortions in Square Planar Complexes?

A Jahn-Teller distortion is predicted whenever a non-linear symmetric molecule has degenerate orbitals and has unequal electron occupation in those degenerate orbitals. Of course, this most often is ...
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Why do most explosives have symmetrical chemical structures?

I was just turning the pages of my chemistry dictionary, when I found the structure of TNT (Trinitrotoluene): ...there after I got interested in its symmetry as an explosive, and started looking for ...
Martin Medro's user avatar
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Derivation of the Orgel diagram for octahedral d2 complexes

The Orgel diagram for a typical octahedral $\mathrm{d^2}$ complex is shown below: (source: Kettle, Physical Inorganic Chemistry, p 146) I understand that the right-hand half of the graph shows how ...
orthocresol's user avatar
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In a molecular dynamics context, is the methyl rotation in propene a symmetric or asymmetric internal rotor?

In a prior question, I asked about the (a)symmetry of the potential energy surface of the methyl rotation of propene. In that context, the kinetic energy of the nuclear motions is of course assumed ...
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Symmetry representations

I'm Having a real struggle trying to understand symmetry representations matrices and character tables. Is there anyone who would be kind enough to help me out here? I understand it is probably a ...
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How do I show that a transition is magnetic dipole allowed with group theory/symmetry?

I am taking an introductory course in symmetry and bonding and have so far learnt about SALCs and various point groups etc... one of my problems asks me to show a $\mathrm{^{2}T_{2g}\rightarrow\ ^{2}...
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Does trans-decalin really have a plane of symmetry?

My teacher told me that trans-decalin (see below) is achiral due to the presence of both, a centre of symmetry and a plane of symmetry. But I could not spot the plane of symmetry untill now. Can ...
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Does the methyl rotation in propene have a symmetric or asymmetric potential energy surface?

Depending on how one imagines the methyl rotation of propene to occur, it seems like it could exhibit either a symmetric or an asymmetric potential energy surface. If the $\ce{H2C=CH\! -}$ portion ...
hBy2Py's user avatar
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How to get the reducible representations of the B-B and the B-Cl bond of B2Cl4

I just can't seem to get the correct answer to this symmetry question in my book. "Introduction to molecular symmetry J.S.Ogden." I am trying to find the reducible representations of both the $\ce{B-...
RedPen's user avatar
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Determining overtones bands of degenerate modes

I have a question of a more mathematical nature on the mathSE (Symmetric Direct Product Distributive?) that received a good answer, but I think an answer more oriented to chemists would be a useful ...
Tyberius's user avatar
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Why is prismane explosive but cubane is not?

So I was reading about polyhedral hydrocarbons, because I dig the topic, and I read (admittedly on wikipedia entries... But they cited papers, I swear!) that prismane is explosive due to the massive ...
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How do I determine the crystal field splitting for an arbitrary point group?

How can I figure out the degeneracy of the d orbitals for a site that has a given point group? Specifically I'm interested in $D_{3d}$ and $D_{3h}$, but it would be good to know how to do it in the ...
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Why does twistronic 'magic angle' graphene have only 180-degree symmetry?

From Graphene superconductors may be less exotic than physicists hoped[1]: Excitement rose earlier this year with the discovery of superconductivity in a similar system[2]: three layers of graphene ...
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Why can anthracene, but not phenanthrene, take part in Diels–Alder reactions?

Both anthracene and phenanthrene seem to be structurally similar, with three aromatic rings. The middle rings in particular seem to be similarly activated towards cycloadditions.
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3 answers
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Why does symmetry have to be maintained in molecular orbitals?

Using the example of $\ce{XeF4}$: What is the physical explanation enforcing the symmetry of the $\ce{1b_{1g}}$ orbital on the fluorine atoms? Why isn't the symmetry of a nonbonding orbital arbitrary?...
Blaise's user avatar
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6 votes
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How derive g and u symmetry labels for orbitals?

When asked whether a molecule has an inversion center, we "invert" the coordinates of all atoms; i.e. move each atom from its position through the center of symmetry and to a new position equidistant ...
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6 votes
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Equivalent Wyckoff position in different groups

I am not a chemist, I am a physicist, so please bare with me if what I am asking is rather obvious. If I have two symmetry groups ($P4/mmm$ and $P\!-\!1$), is there a way to find their respective ...
M.O.'s user avatar
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1 answer
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Does 1,3-dichloroallene possess a C2 symmetry axis?

Is there an $C_2$ axis of symmetry in $\ce{Cl-CH=C=CH-Cl}$? A $C_2$ axis of symmetry means that I should be able to rotate the molecule about an axis by $180^\circ$. But I would need a composition ...
gauri agrawal's user avatar
5 votes
0 answers
485 views

Determining the lowest rank non-vanishing multipole moment [closed]

I have been told that the multipole moments of rank 0,1,2,3,...n have respectively 1,3,5,7,...2n+1 components which transform like the spherical harmonics of rank 0,1,2,3,...n. How do I use the ...
user91820's user avatar
4 votes
3 answers
5k views

Methane T2 SALCs

So I have a question on the form of the $T_2$ SALCs of methane. Below I show the $T_d$ character table and the accompanying reducible representation for the sigma framework (using, in the case of ...
Yajibromine's user avatar
4 votes
1 answer
346 views

Molecular orbitals symmetry - states notation

I'm reading some papers and I'm repeatedly seeing the following notation of system states: Could you, please, explain to me the meaning of it? E.g. the state $B^2 \Sigma_u^+$ - I'm aware, that $\...
Eenoku's user avatar
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Why is CO2 not in the C∞v point group?

It seems to me that CO2, since it can be linearly rotated around the z-axis without change of shape, ought to be in the C∞v point group. However, in all the character tables I can find, it's listed ...
anonymous2's user avatar
3 votes
1 answer
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AB5E type molecule

In $\ce{AB5E}$-type molecules, why are the lone pairs in axial bonds? If the lone pair is present in axial bonds it repels four other bonds. On the other hand if the lone pair is in equatorial ...
Kaushik's user avatar
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1 answer
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How do we find the SALCs?

I am trying to understand exactly what IRREPs are and, in order to know more about it, I started reading the chem.libretext course on molecular symmetry which up to this point seemed fairly ...
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Group Theory and Chemistry for Undergraduate Thesis

I am advising a student on her senior math thesis. She would like to involve chemistry somehow (her other major). I know no chemistry. I have read in several places that representation theory ...
J126's user avatar
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1 answer
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Molecular Orbitals (only pi system) of Allyl system using group theory

I have just started reading group theory and their applications in the MO theory. I tried to get the equations of the pi molecular orbitals of allyl system using group theory, but I am stuck at the ...
S R Maiti's user avatar
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How to systematically find the reducible representation of a molecule? (eg: XeF4)

I am attempting to use the reduction formula to find the irreducible representation of $\ce{XeF4}$ to determine its IR stretching vibrations. I know the point group of $\ce{XeF4}$ is $D_{4h}$ and have ...
Tetraquark's user avatar
1 vote
1 answer
483 views

What is the criteria for determining structure of a molecule?

Does the shape of the molecule depends on symmetry? Why is the shape of dinitrogen trioxide ($\ce{N2O3}$): (oxidation number of nitrogen atoms: +4, +2) Instead of my proposal, which is much more ...
Swastik's user avatar
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1 vote
1 answer
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Conditions for molecular dissymmetry

In my textbook, under the topic "Asymmetric and Dissymmetric Compounds", the following statement is given: A molecule which does not possess plane of symmetry, centre of symmetry, and alternating ...
Vishnu's user avatar
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-1 votes
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What is cn axis of symmetry [closed]

While reading about axis of symmentry and I'm not able to comprehend what does C infinite or rather n signify in a molecule I know axis of symmetry is the axis along which rotation of molecule ...
suhani Mahajan's user avatar