All Questions
Tagged with molecular-orbitals or molecular-orbital-theory
222 questions with no upvoted or accepted answers
10
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0
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Orbital and state correlation diagram for ring-closure of pentadienyl to a cyclic allyl
This is an exam question. I am to construct the orbital and state correlation diagram for one of the reaction below (disrotation or conratation). Also, I should explain whether the reaction is ...
- 4,773
9
votes
0
answers
206
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Is there a reliable chemical theory that predicts pKa based on structure?
Obviously, there are general stability arguments that can be made to estimate relative pKas, such as evaluating the stability of the conjugate base of an acid, or thinking about how polarized the bond ...
- 732
9
votes
0
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938
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Free Web-Based Orbital Solver to look into the Walsh orbitals of a perturbed cyclopropane
There exists a free online orbital calculator.
When I draw cyclopropane it plots three molecular orbitals, but unfortunately it doesn't use the Walsh orbitals.
Are there any free online tools which ...
- 3,405
8
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0
answers
280
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Why is octaoxygen diamagnetic?
I tried considering that according to LCAO-MO theory $\ce{O2}$ is paramagnetic, which is confirmed by experimental evidence. Since octaoxygen has the crystal structure in figure, I thought there is a ...
- 189
8
votes
0
answers
653
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Bond orders in the 3c-4e bond and 3c-2e bond
According to D. P. M. Mingos, in his book Essential Trends in Inorganic Chemistry, the bond order of the three-centre four-electron bond is approximately 0.717, which is one divided by the square root ...
- 10.8k
7
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0
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186
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Is the 9H-fluoren-9-ylium cation aromatic?
In this cation, there are two individual benzene rings which are aromatic. But in the entire π system, there are 12 π-electrons which should make it antiromatic. Which is correct?
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6
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0
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476
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How to explain oxidizing power from Molecular Orbital Theory
I am trying to explain the oxidizing property of $\ce{Fe^3+}$ in $\ce{H2O}$ and $\ce{CN^-}$ which is $\ce{[Fe(H2O)6]^3+}$ and $\ce{[Fe(CN)6]^3-}$.
The electrochemical reactions along with their ...
- 651
6
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0
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79
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Why SCF-MO methods fail when treating bond-breaking processes?
I'm currently studying the EVB(Empirical Valence Bond) approach. While reading on this article (https://pubs.acs.org/doi/10.1021/ja00224a011), the author mentioned about the usage of SCF-MO formalism ...
- 221
6
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0
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144
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How do bonds rotate in pericyclic reactions?
In Pericyclic reactions, it is shown that the terminal bonds rotate (conrotation or disrotation) to allow for allignment of the FMO's, thereby forming the sigma bond
However, a detail that most of my ...
- 6,338
6
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0
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193
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Is any symmetry element conserved during a supra-antarafacial cyclo addition of two cis-butadiene units
I tried to construct a correlation diagram for the [4+4] cyclo addition of two cis-butadiene units. But I failed to construct any meaning full orbitals for the "educt" side where the two butadiene ...
- 1,300
6
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1k
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Platt's Notation/Nomenclature for transitions
How do you read Platt's Notation / Nomenclature? Where can I learn this?
Some examples where I've seen this mentioned:
In Platt's notation the transitions are designated as $\ce{A -> B}$ and $\ce{...
- 521
5
votes
0
answers
654
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Explanation of the trans-effect (thermodynamic and kinetic) for octahedral transition metal complexes
The thermodynamic trans effect refers to the ground state weakening of the metal-ligand bond in a complex by a ligand trans to it. The kinetic trans effect is the lablisation of a ligand in a complex ...
- 5,735
5
votes
0
answers
523
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Orbital Interaction for electrophile and nucleophile
Clearly, the above diagrams depict the interaction between empty orbital of electrophile with filled orbital of nucleophile. We may assume that the HOMO of nucleophile being more electronegative will ...
- 805
5
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0
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336
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Molecular orbital diagram for carbene-metal and carbodiphosphorane-metal interaction
I am interested in understanding how carbenes and carbodiphosphoranes interact differently with a transition metals. I would like to use qualitative molecular orbital theory arguments (with an ...
- 4,773
5
votes
0
answers
409
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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 ...
- 1,240
5
votes
0
answers
77
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Identifying principal quantum numbers in natural population analysis
Following a Hartree-Fock calculation, I would like my program to perform some kind of Natural Bond Orbital (NBO) analysis. Preceding this I would like to output a list of atomic orbitals, along with ...
- 1,271
5
votes
0
answers
174
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How to calculate a molecule's oscillator strength?
I was wondering how to calculate a molecule's (e.g. biphenyl) oscillator strength using a very simplified model.
If I want to calculate a molecule's excited states a good start is something like a ...
- 369
5
votes
0
answers
143
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Relative orbital energies of Mn and Ni
In this MO diagram, why are the atomic Mn $3d$ orbitals higher in energy than the Ni $3d$ orbitals?
- 67
5
votes
0
answers
1k
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On baker nathan hyperconjugation
Recently I have been reading about the history of the Baker Nathan reaction.
In addition to the large
rate increase for Me vs H, all the other alkyl groups
showed decreases with respect to Me ...
- 698
5
votes
1
answer
166
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How does one calculate chemical shift in a gauge independent manner?
The literature on ab initio calculations of chemical shift in NMR experiments usually provide Lamb's and Ramsey's formulae as the solution. Yet the expressions explicitly depend on vector potential ...
- 145
4
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0
answers
129
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What is the driving force of Bartoli indole synthesis?
The Bartoli indole synthesis mechanism begins with a series of attacks on the nitroarene regent by the Grignard reagents. But the atom $\ce{O}$ in $\ce{-NO2}$ should be negative, and Grignard reagent ...
- 49
4
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0
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255
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Electronegativity, polarity, pi bonds, and nitriles
While googling some numbers, I found that the dipole moment of acetonitrile is, according to wikipedia 3.92D. Compare this to the dipole moment of ethylamine, according to NIST of 1.220D. Now, I've ...
- 141
4
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0
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548
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Does (BeCl2)n have 3-center-4-electron-bonding or not?
The title really explains what the issue is here. I would think that it has multicenter bonding akin to $\ce{(BeH2)_n}$ polymer, because they are pretty much iso-structural (although it shouldn't have ...
- 1,524
4
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0
answers
207
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How to read character table?
I am having some problems reading character table. I will describe what I understand and thought to be right.
Consider the $\pi$ MOs formed from overlap of p-orbitals in benzene.
These two degenerate $...
- 1,241
4
votes
0
answers
93
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
4
votes
0
answers
476
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Symmetry Adapted molecular orbitals of Formaldehyde
I am currently trying to find the Symmetry Adapted linear Combinations (SALCs) of Formaldehyde $\ce{H2C=O}$, and use the 1s orbitals on the hydrogen atoms, and 2s, 2px, 2py and 2pz orbitals on the ...
4
votes
0
answers
367
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Molecular orbital diagram of CO and charge localisation
MO diagram of CO
My question concerns the interpretation of the Molecular Orbital of CO. I think I find it clear how you build it but I have some concerns about how you rationalize it.
Particularly, ...
- 93
4
votes
0
answers
761
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Molecular orbital diagram for I₃⁺ cation
Do I need to go through the whole process of reducible representations/projection operator method to come up with the bent SALCs for the $\ce{[I3]+}$ molecule? Or is it simpler than that?
- 347
4
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0
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482
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What exactly are the frontier orbitals in diradical species like O2?
I read about frontier orbitals, namely HOMO, LUMO. But what's exactly HOMO/LUMO? I know HOMO stands for highest occupied molecular orbital and LUMO stands for lowest unoccupied molecular orbital.
But ...
- 1,350
4
votes
0
answers
5k
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Why CO is a stronger and more common ligand than N2?
Both $\ce{N2}$ and CO are considered sigma-donors and pi-acceptors.
Their molecular orbital diagrams are also similar, so why does CO generally bind more strongly and is a more common ligand?
- 1,859
4
votes
0
answers
309
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Variational method: Hydrogen atom ground state in STO-3G basis expansion
I computed numerically the ground state energy of hydrogen by variational procedure, firstly expanding the wave function over the s-wave basis set STO-3G
$$\psi(r)=\sum_{i=0}^3 C_{i} e^{-\alpha_ir^2}$$...
- 51
4
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0
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120
views
Is the concept of frontier orbital interactions chiefly a kinetic concept?
Frontier molecular orbital theory has proved to be an immensely useful concept. The concept of HOMO-LUMO interactions are frequently employed in detailing the mechanistic descriptions of reactions in ...
- 10.8k
4
votes
0
answers
92
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Rhombohedral second-order Jahn–Teller effect in Au(II) complex?
I was recently listening to a talk about the following work[1] when the author mentioned that they explained the following. In this $\ce{Au(II)}$-porphyrin complex you observe two sets of $\ce{Au-N}$ ...
- 4,362
4
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0
answers
307
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Oscillator strength of a transition
I am trying to compute the oscillator strength in a molecule. Therefore I've got its Energy level values plus both wave functions $\Psi_i$ and $\Psi_j$ for the transition I want to calculate the ...
- 369
4
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0
answers
2k
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Trends in pi backbonding for main group elements across a period
Recently, I have been re-reading some undergraduate notes and found that there's a period trend in pi backbonding of main group elements (i.e. no transition metals involved) but no explanation were ...
- 698
4
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0
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185
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Stability of unsaturated syn/anti 3-ladderane
In an oral exam for physical organic chemistry, one student was asked to explain the differences in the ionization potential ($IP$) of syn and anti tricyclo[$4.2.0.0^{2,5}$]octa-3,7-diene (unsaturated ...
- 662
4
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0
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889
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Is the para-position of anisoles more reactive than ortho in electrophilic substitutions?
In my group’s seminar last Friday, we discussed the total synthesis of 6-demethyl-6-deoxytetracycline 1 by Woodward et al.[1] One intermediate of their synthesis is meta-substituted anisole 2 that ...
- 68.7k
3
votes
0
answers
94
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How do I derive the second-order mixing coefficient from Perturbational Molecular Orbital (PMO) Theory?
Hi I need help deriving a result from the PMO theory. I'm currently reading the second edition of the book Orbital Interactions in Chemistry by Thomas A. Albright, Jeremy K. Burdett & Myung-Hwan ...
- 51
3
votes
0
answers
77
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The MO diagram of sulfur hexafluoride?
Although I have seen it explained, I haven't seen a MO diagram of SF6 on this website showing LCAO - only written explanations and vague diagrams. I was wondering if anyone could share the MO diagram. ...
- 128
3
votes
0
answers
109
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How to interpret molecular orbital (HOMO - LUMO) plots in Chem3D 22.0?
Recently, I have been trying to understand the origin of the difference in reactivity of alkynyl-boron(ate) complexes so I tried to generate a molecular orbital plot on Chem3D (Version 22.0.22 64bit) ...
- 1,342
3
votes
0
answers
2k
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Molecular Orbital Diagram of NO
When we draw the molecular orbital diagram for molecules
For those that have less than or equal to 14 electrons we use the order "σ1s σ∗1s σ2s σ∗2s π2px,π2py σ2pz π∗2px,π∗2py σ∗2pz"
and for ...
- 31
3
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0
answers
60
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Is an element's "atomic electron configuration" EXACTLY equal to the term with the largest coefficient in the CI series of the neutral atom?
For atoms and molecules with more than one electron, the wavefunction cannot be written as a single Slater determinant, so the ground-state configuration of (the atom or molecule in question) is ...
3
votes
0
answers
295
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Can cycloaddition reactions be antarafacial?
Cycloaddition reactions of the form [4+2] and [2+2] are always suprafacial, as the geometry is too constrained to allow for antarafacial interaction between the FMO's. However, for cycloaddition of ...
- 6,338
3
votes
0
answers
135
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(Mis)understanding on MOT
In VBT, one can understand the example of hydrogen like this - Two hydrogen atoms come closer to each other, and their orbitals overlap, stabilize, and ultimately result in a bond. This is not too ...
3
votes
0
answers
57
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Why is 4-t-butyl aci-nitro cyclohexane stable whereas aci-nitro cyclohexane is not?
During my PhD, about fifty years ago, I had reason to use 4-t-butyl aci-nitro cyclohexane and found it to be remarkably stable. Usually aci- nitro compounds revert to nitro compounds very quickly ...
3
votes
0
answers
75
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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 ...
- 438
3
votes
0
answers
346
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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 ...
- 1,240
3
votes
0
answers
302
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Protonation of pyridine
Recently, I have been reading the Nobel Lecture given by Kenichi Fukui when he won the Nobel Prize in 1981, for his contributions to the development of Frontier Molecular Orbital Theory. One of the ...
- 10.8k
3
votes
0
answers
358
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Implementing the projected atomic orbital (PAO) localization in Gaussian
I am currently attempting to learn how to setup the active space for performing CASSCF calculations.
The textbook I am using as a reference is:
Roos, Björn O. "Multiconfigurational quantum ...
- 1,026
3
votes
0
answers
281
views
Hückel method for biphenyl
I am trying to calculate the energy levels of biphenyl (see picture below) using Hückel method. Since this is my first time using Hückel I am a little confused.
Biphenyl has 12 carbon atoms, ...
- 369