Questions tagged [molecular-orbital-theory]
Use of molecular orbital (MO) theory allows for an understanding of the observed properties (shape, reactivity) of molecules. The tag should be applied to all questions related to MO theory, from questions about the qualitative use of the theory to questions about the underlying quantum mechanics and applications in computational chemistry.
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Valence Bond Theory and double sigma bonds [closed]
I naively use Valence Bond Theory to analyze dicarbon.
Both carbons spontaneously excitate from 2s2 2p2 to 2s1 2p3.
Both 2s orbitals overlap head-on to form a sigma bond.
Both 2pz orbitals overlap ...
1
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1answer
271 views
Electron pairing in atoms
A question asks:
This question refers to isolated gaseous atoms. In which atom are all electrons paired? Ba, Br, S or Si?
I thought it was Ba as its electron configuration is [Xe] 6s2.
However, ...
2
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0answers
35 views
Why does the binding of DMSO to metal via the S atom (k-S) strengthens the S=O bond?
So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\mathrm{\kappa O}$ and $\mathrm{\kappa S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given ...
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40 views
Hybridized orbitals and molecular orbital theory
When hybridization was introduced in the late 30's to explain the structure of methane , first it was considered that bonds between valence electrons of carbon in different atomic orbitals will have ...
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0answers
11 views
MO analysis of a radical reaction of chlorine radical with methyl radical
Im trying to create an MO energy diagram for the reaction of a chlorine radical with a methyl radical by creating the 5 group orbitals for methyl radical(with pyramidal geometry) and then creating ...
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29 views
Does the number of bonding MOs always equal the number of antibonding MOs
In (I think all) of the molecular orbitals (MO) diagrams I have seen, I have observed that the number of antibonding molecules is the same as the number of bonding molecular orbitals.
Here are some ...
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1answer
60 views
Why is the HOMO-LUMO gap in N2 and CO of different sizes? [closed]
Why is the HOMO-LUMO gap in $\ce{N2}$ and $\ce{CO}$ different even though they have the same number of valence electrons?
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How many π-electrons are there in 2-methylene-2H-pyran?
I thought that the structure will be aromatic and stabilised because one of the lone pairs being delocalised with the help of conjugated double bond system but still only 3 π-bonds will be present at ...
2
votes
1answer
161 views
Geometry of Ni(acac)2
The complex $\ce{Ni(acac)2}$ is paramagnetic as expected , i.e it has two unpaired electrons giving rise to a magnetic moment of $ \sqrt{8}$ BM but doesn't have the tetrahedral geometry consistent ...
1
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1answer
18 views
Mathematical equivalence of ionic-bond resonance structures and d-orbital participation in hypervalent molecules
It is now routine in the scientific community that "main-group hypervalent molecules, under certain conditions, tend to be better represented by resonance structures involving ionic bonds, rather than ...
3
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1answer
65 views
How to perform Mulliken population analysis by hand with GAMESS output?
I did a simple calculation on hydrogen fluoride with GAMESS and I wanted to reproduce the Mulliken population analysis for atomic orbitals.
A molecular orbital is a linear combination of atomic ...
1
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0answers
20 views
pi-type bonding interaction along the bond
I was given the diagram of $\ce{BF3}$'s LUMO and asked to assess its bonding character as shown below:
Below is the model answer for the annotated version.
I managed to correctly answer the HOMO MO ...
0
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0answers
99 views
Molecular orbital diagram of hydroxide ion?
I would like to understand how to create a molecular orbital diagram for the hydroxide ion from scratch. This includes understanding the shape of the molecular orbital.
Here is an attempt I have come ...
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0answers
19 views
Books for organic chemistry [duplicate]
What is the best book to start organic chemistry once I know the basic knowledge of reaction mechanisms like substitutions (nucleophilic, electrophilic and some basic other mechanisms that are given ...
3
votes
1answer
46 views
Symmetry of an FO
I want to ask a question about the symmetry of an FO for $\ce{[CuL2]^-}$ where L is a $1e^-$ donor sigma bonding ligand (e.g. Me).
For the ligand orbitals, I produced the following orbitals shown ...
0
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2answers
80 views
Questions in MO theory
Τhe electrons in the antibonding MO are the unpaired electrons of the molecule? E.g. $\ce{O2}$, by writing down the diagram for the MO we notice that there are only 2 electrons in the top antibonding ...
4
votes
1answer
59 views
How to understand the (non-)degeneracy of states of singlet Σ and Δ terms for a ππ configuration of two nonequivalent electrons?
As instructed in Levine's Quantum Chemistry 7th edition, Chapter 13.8, page 377, for a $\pi \pi$ configuration of two nonequivalent electrons, four functions $\pi_{+1}(1) \pi_{-1}^{\prime}(2)$, $\pi_{+...
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0answers
21 views
Energy Levels of Molecular Orbitals formed by combination of Atomic Orbitals
In general when we talk about chemical bonding, we say that it is "nature's way to stabilize the systems" and the energy of the molecule formed by atoms will be lower than that of the individual atoms;...
2
votes
1answer
78 views
Effective Bohr Radius in Transition Metal Complexes?
I am playing around with a toy model of a transition metal complex where the HOMO are $d$-electron states of predominantly transition metal character. Let's say this is a $d^1$ (or $d^9$) system and ...
1
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0answers
9 views
Energy diagram of copper iodide complex
We did an experiment where copper iodide 4-methylpyridine and copper iodide imidazole was formed and now we are asked what orbital the electron is excited from and to.
After much research we still ...
9
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1answer
120 views
Hybrid orbitals, photoionization and time dependence
Wikipedia, in the article on Orbital Hybridisation, states the following:
One misconception concerning orbital hybridisation is that it incorrectly predicts the ultraviolet photoelectron spectra of ...
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1answer
41 views
Question about d-orbitals [closed]
I saw somewhere that, "in PF5, the 3d orbitals of phosphorus end up in the anti-bonding molecular orbitals, and thus contribute less to the final molecule" and that "the hypervalency of some ...
4
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1answer
305 views
Question about the role of d-orbitals in polarisation
I know that, although many elementary books say that d-orbitals are involved in the bonding of hypervalent main group compounds period 3 or higher such as the sulfate ion but in reality they are only ...
3
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0answers
42 views
Overlap matrix for finite sized square lattice of hydrogen atoms
So I'm trying to use the LCAO method to calculate molecular orbitals on a square lattice of hydrogen atoms. To this end, I need to compute the Hamiltonian matrix. With the nearest neighbor interaction ...
0
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1answer
58 views
Why must there be degeneracy in the orbitals to have a Jahn-Teller effect? [closed]
Why is it the case that for Jahn-Teller effects to occur in transition metals there must be degeneracy in either the $\mathrm{t_{2g}}$ or $\mathrm{e_g}$ orbitals?
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Sigma bond by combining two p orbitals
If I combine two p orbitals in such a way that they form σ bonds, which linear combination will represent bonding and antibonding?
My work on this problem:
$$
\begin{align}
&\text{Bonding:} &...
3
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0answers
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Energy level of molecular orbitals in heteronuclear diatomic compounds
I have been studying the molecular orbital theorem. I read that the energy levels for the $\ce{p}$ orbitals in the first series of $\ce{p}$ block molecules are something to the tune of $$\pi_x=\pi_y&...
7
votes
1answer
160 views
Energies of Virtual Molecular Orbitals (LUMO)
I just had a question about molecular orbitals. I was just wondering if the energies of the LUMO (virtual orbitals) derived from CCSD(T)/cc-pTVZ calculations could be trusted. I remember reading some ...
2
votes
1answer
69 views
Is there a hypervalent molecule which has no contribution of d-orbitals at all?
I thought that d-orbitals were used to "extend the octet rule" in these molecules until I looked it up on Google and saw that they actually contributed only a little to the molecule. A little, but not ...
2
votes
1answer
75 views
Relative Energies between LGOs and 2s orbital of oxygen in H2O MO Diagram
In this MO diagram, we find that the LGOs of the two premixed H1s orbitals are significantly higher in energy than oxygen's 2s orbital. Although oxygen's $Z_{eff}$ is considerably higher, is it really ...
4
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1answer
95 views
On mathematics behind molecular orbital energies
When explaining the mathematics behind calculating molecular orbital energy , namely HOMO and LUMO energies, using quantum chemistry, Chainer Chemistry documentation states that
From mathematical ...
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0answers
200 views
Mathematical relation between bond angle and fraction of s or p character
In Concise Inorganic Chemistry by J.D.Lee (Adapted by Sudarsan Guha, Fourth Edition), on page 75, under the topic "Effect of Electronegativity - When the surrounding atom is same with different ...
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31 views
Stabilizing donor-acceptor interaction between orthogonal orbitals in the SN2 transition state?
For the $\mathrm{S_N2}$ reaction between chloroacetone and iodide, my professor has drawn a donor-acceptor interaction between the iodine lone pair attacking the Cl-substituted carbon and the π ...
5
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0answers
146 views
diborane fragment orbitals energy of dihydrogen
I want to ask a question about the fragment orbitals of the $\ce{B2H6}$ system, specifically when I combine the $\ce{B2H4}$ with the $\ce{H2}$ fragments.
I am halfway through my inorganic chemistry ...
2
votes
0answers
33 views
Varying sizes in LUMO of acrolein
I want to ask a question about the varying sizes in the LUMO of acrolein during a 1,2- or 1,4-addition.
Today in our introductory lesson to Organic Synthesis with 1,2- and 1,4-addition we were ...
2
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0answers
21 views
How to deal with non-symmorphic space groups for orbital/vibrational analysis?
I am learning about how to apply group theory analysis of MO diagrams and vibrational in the solid state context (not isolated molecules).
I think the strategy for calculating representations and ...
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votes
1answer
135 views
Sulfur can violate the octet rule because it has an “empty D orbital” is there any other information the periodic table isnt telling us?
In sulfur or any atom with an expanded octet on the 3rd row, where does the idea that they have an empty D orbital come from ?
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Calculating the Molecular Orbitals of a Molecular State [closed]
I am performing ab initio calculations on a heteronuclear diatomic compound using the MRCI method on the MOLPRO quantum chemistry package. I obtained the molecular states of the compound but I was ...
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0answers
208 views
What is the purpose of phase matching when drawing a MO diagram?
During the lecture, we were learning how to draw the MO diagram for $\mathrm{BF_3}$.
I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My ...
2
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0answers
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Properties that probe electron kinetic energy
This post is inspired by a question regarding the meaning of off-diagonal elements of the KE matrix (in some AO basis). One answer suggests that a diagonalized KE matrix might not be very useful. I ...
2
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1answer
228 views
Molecular orbital energies prediction with ML algorithms
In the recent years, computational chemistry community has focused on Machine Learning algorithms to predict molecular properties. Unfortunately, many of the authors of such papers are not chemists, ...
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1answer
67 views
Based on Molecular Orbital Theory , how is it decided that the double bond in O2 molecule has one sigma bond and one pi bond?
My Chemistry textbook says this in regard to a C2 molecule:
It is important to note that double bond
in C2 consists of both pi bonds because of the
presence of four electrons in two pi ...
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0answers
34 views
Is Octet Expansion appropriate when regular Octet bonding is possible (such as using dative bonds)?
I was taught to use Occam's razor whenever in doubt over an octet expansion, being told it never happened when, for example, dative bonds could resolve the issue with a regular octet. This seems to ...
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0answers
32 views
Two questions about MO diagrams [duplicate]
In $\ce{HF},$ the $\mathrm{1s}$ orbital of $\ce{H}$ matches the $\mathrm{2p}$ orbital of $\ce{F}.$ However, in $\ce{LiF},$ the $\mathrm{2s}$ orbital matches the $\mathrm{2p}$ orbital. I knew that the ...
2
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0answers
43 views
Finding out more stable conformer via molecular orbital interaction
Out of these two, which one is more stable? I'm unable to imagine the orientation of the lone pairs of O and ABMO of C and Cl bond.
Any tips to tackle these kind of problems?
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Explanation of SN2 Mechanism using MOT
SN2 is usually explained by MOT, where we state that the incoming nucleophile starts donating the electron density into the σ∗ orbital and the carbon-leaving group bond weakens and finally breaks and ...
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Why are sulfur trioxide and nitrate not isoelectronic, even though both have the same number of outer electrons?
Though $\ce{SO3}$ has the same number of outer electrons as $\ce{NO3-}$, the two are not isoelectronic.
This statement is from JD Lee, but I could not understand why is he calling these two molecules ...
2
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0answers
547 views
Why CO is a stronger and more common ligand than N2?
Both N2 and CO are considered sigma-donor and pi-acceptor. Their MO diagram is similar, so I wonder why CO binds generally more strongly and it is a more common ligand.
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1answer
52 views
Cycloaddition vs Electrocyclic Pathway [closed]
Is there a molecular orbital/Woodward-Hoffmann explanation as to why Diels-Alder reactants don't commonly undergo electrocyclization instead of cycloaddition?
1
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1answer
134 views
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 ...
