All Questions
Tagged with symmetry physical-chemistry
26
questions
34
votes
1
answer
10k
views
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 ...
- 2,757
25
votes
1
answer
4k
views
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 ...
- 71.6k
13
votes
2
answers
2k
views
Rule of mutual exclusion: is the converse true?
There is a "famous" rule in spectroscopy,1 that goes this way:
If a compound is centrosymmetric, then its normal vibrational modes cannot be simultaneously IR and Raman active.
and this is simple ...
- 71.6k
10
votes
2
answers
3k
views
Is there a physical explanation why benzene's pi molecular orbitals in a Frost circle are degenerate but pyridine's are not?
From here, the Frost Circles for both benzene and pyridine:
The $\pi$-MOs formed by 6 $\pi$-AOs of an aromatic ring are:
Listed with respect to the ordering in the above image, these MOs in benzene'...
- 1,648
10
votes
0
answers
172
views
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 ...
- 17.4k
9
votes
1
answer
506
views
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 ...
- 17.4k
8
votes
1
answer
3k
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Determination of +/- reflections in sigma molecular term symbols
This page, which depicts the molecular term symbols for the $\ce{O2}$ and $\ce{O2-}$ (Edit: Mistaken on $\ce{O2-}$) molecules, perhaps best summarizes the full scope of my questions. In general, I don'...
- 1,648
7
votes
2
answers
854
views
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 ...
- 731
6
votes
2
answers
364
views
Potential wells and symmetry in absorption spectroscopy
In a course I am following, we are analyzing the potential wells in molecular absorption spectroscopy.
For molecules with more than one normal mode, we can study the potential wells involved in ...
- 163
6
votes
1
answer
1k
views
Rotovibrational selection rules for symmetric tops
The selection rules for symmetric top molecules are
$\Delta J = 0, \pm1$ and $\Delta K = 0$ for $K \neq 0$ (parallel transition)
$\Delta J = \pm1$ and $\Delta K = 0$ for $K = 0$ (parallel ...
- 1,696
5
votes
1
answer
2k
views
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
...
- 155
5
votes
0
answers
185
views
Analysis of metal carbonyl bonding in Fe(CO)5 using molecular orbitals
I am really struggling with this question we have been set in class:
Metal-carbonyl bonding: Conceptionally, one can build up $\ce{[Fe(CO)5]}$ from the $\ce{Fe(CO)4}$ fragment plus free $\ce{CO}$ in ...
- 51
4
votes
0
answers
89
views
Symmetry Operation on Product of Functions
In regards to direct product representations, I'm trying to find a proof for:
$R(X_iY_j)=R(X_i)R(Y_j)$
Where $R$ is a symmetry operation of a group and $X_i$ and $Y_j$ are members of different basis ...
- 41
3
votes
2
answers
1k
views
Are there different types of symmetry? [duplicate]
What factor does the symmetry of a molecule play?
For example, I know water is asymmetric so does this therefore make water polar (I know in fact that is is)? It may sound ignorant due to my lack of ...
- 435
3
votes
1
answer
178
views
Solution of the Roothaan Equations of H2 by Symmetry Arguments
FWIW my background is in physics and maths, but I am just starting a chemistry PhD (the last time I took a chemistry class was high school). I have only some background in representation theory, and ...
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