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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1answer
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Why is the endo product the major product in a Diels-Alder reaction?

I understand that the endo product is, at least in all cases in my textbook, the major product in a Diels-Alder reaction. However, I don't understand why this is the case. The explanation in my ...
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0answers
106 views

Can pi backdonation occur on non-metal centers?

The common example of back-donation is the interaction of a CO molecule with a metal center (d-orbitals) on a surface. Can a similar mechanism occur between CO and a non-metal center, like oxygen on ...
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0answers
590 views

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 ...
9
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0answers
449 views

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 ...
9
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1answer
136 views

Justifying the tremendous -I effect of -[NMe₃]⁺ by molecular orbital theory

The $\ce{-[NMe3]+}$ group is ranked almost at the first position in the -I effect series, which is often given at the very beginning of the teaching of general organic chemistry. I know this can be ...
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239 views

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 ...
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83 views

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?
6
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144 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 ...
6
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106 views

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 ...
6
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442 views

Chemical bonding with f orbitals

For the elements such as rhenium, osmium, iridium how probable is for electrons in the inner 4f orbitals to gain energy and take part in a molecular orbital (such as an $f^2 d^2 s p^3$ hybrid orbital) ...
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834 views

What does Molecular Orbital Theory get wrong?

I am learning about MO theory in my advanced inorganic chemistry course and am starting to realize that it is truly the most accurate representation of how molecular orbitals look like, where they are ...
5
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87 views

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 ...
5
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60 views

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 ...
5
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93 views

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 ...
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344 views

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 $\...
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97 views

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?
5
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1answer
139 views

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 ...
4
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76 views

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 $$\psi(r)=\sum_{i=0}^3 C_{i} e^{-\alpha_ir^2}$$...
4
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40 views

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
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1k views

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 ...
4
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918 views

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 ...
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149 views

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 ...
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663 views

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 ...
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18 views

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&...
3
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73 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 ...
3
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44 views

Why is triatomic hydrogen relatively short-lasting?

The first chapter of Fleming's "Molecular Orbitals and Organic Interactions," describes the formation of triatomic hydrogen. In summary, the sigma MO of diatomic hydrogen interacts in phase with the ...
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158 views

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 ...
3
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1answer
160 views

Formation of trifluoride anion

I wanted to understand mechanism of the formation of $\ce{F3-}$ anion through the molecular orbital theory. UPDATE - What I really want to know is that when $\ce{F3-}$ is formed from $\ce{F2-}$ and $\...
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113 views

stability and energy gap

We know that the lower the energy gap between bonding and antibonding orbital the easier it is to break the bond making it unstable. However, in a conjugated double bond, the overlapping of ...
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271 views

Negative hyperconjugation stabilizes tricyclopentane derivate

As far as I know, negative hyperconjugation means, that we have electrons that are transferred from a p- or $\pi$- to a $\sigma^*$-orbital. In the lecture, we analyzed a TMS-substituted ...
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23 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 ...
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16 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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0answers
26 views

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 ...
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0answers
39 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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246 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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38 views

Electronic States of the (unstable) tetrahedral CrCl4

I was probing for first order Jahn-Teller instability in the coordination complex CrCl4 (2 electrons in E set). Taking the direct product yields the states A1 + A2 + E, so I took the symmetric and ...
2
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0answers
56 views

HOMO orbitals of B-N from an MO diagram

I want to ask a question about the MO diagram of BN. I was provided with the following question and answer and describe the situation occurring: After performing the s-p mixing for BN, I found this ...
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0answers
45 views

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 ...
2
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0answers
25 views

Do species with more unpaired electrons attract magnets more strongly than those with fewer unpaired electrons?

My lecture notes state that you can distinguish between high spin and low spin complexes by their magnetic properties. This thought came to me: consider two octahedral crystal fields with a d7 ...
2
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0answers
77 views

Hydrogen Bonding in Water (MO theory)

Valence Bond Theory tells us that each of the “sp3” (in reality, 44% s character) oxygen line pairs in water can act as electron donors, but observing the MO diagram for water tells us that the 2 non-...
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0answers
55 views

Theory of symmetry breaking in water?

As we all know $\ce{H2O}$ is bent ($C_\mathrm{2v}$) in its ground state equilibrium structure, rather than linear ($D_\mathrm{\infty h}$), which can be readily understood e.g. from the MO diagram of ...
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0answers
175 views

Structure of (CH3COO)3Fe

I'm a grade 12 student trying to comprehend MOT & LFT in Co-ordination compounds. For one of our salt analysis(practicals), the test for acetate ion includes the addition of Neutral Ferric ...
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62 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 ...
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37 views

Calculate molecular orbitals of high-lying or Rydberg states in GAMESS (US)

I am trying to calculate the high-lying or Rydberg orbitals (i.e. unoccupied orbitals with their energies just below the ionization energy) of a nitrogen molecule. I use GAMESS(US) with the following ...
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0answers
236 views

Could Be2- exist?

I understand that Be2 cannot exist, since it has as many electrons in the antibonding as in the bonding orbitals. But it seems to me that since the next electron would go into the πu orbital, which ...
2
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0answers
38 views

Can LCAO be seen as superposition?

In wave physics, when waves interact, the principle of superposition applies. It states that the displacement of the resultant wave is made up of the sum of the individual displacements of the ...
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0answers
88 views

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 ...
2
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0answers
27 views

GVP(PP) orbital energies?

Hartree-Fock orbital energies can be interpreted physically, e.g. in Koopmans theorem, while one cannot assign active MCSCF orbitals to energies in general. What about GVB, say for example GVB(PP) ...
2
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0answers
105 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, ...
2
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0answers
97 views

Which natural orbitals are better for CASSCF calculations for organic diradicals?

I am trying to perform CASSCF calculations for a series of diradicals. As input orbitals I have used two types of natural orbitals. One is unrestricted natural orbitals and the other MP2-based natural ...