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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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4
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1answer
158 views

Rationale for assigning antibonding MOs

How do people decide if a molecular orbital (MO) is bonding or antibonding? From Wikipedia article on antibonding MO: [...] if the antibonding interactions outnumber the bonding interactions, the ...
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0answers
172 views

The affect of effective nuclear charge on energy gap between subshells

A few days ago my teacher taught me about $\mathrm{d}$ orbital contraction. He said that in $\ce{SF6}$ the hybridization of sulphur is $\mathrm{sp^3d^2}$. He said that although the $\mathrm{d}$ ...
7
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1answer
236 views

Molecular Hamiltonian of Helium hydride ion

Currently, I am going through Quantum Simulation of Helium Hydride Cation in a Solid-State Spin Register. I am not a chemist but rather a computer scientist hence having trouble following the paper. ...
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2answers
275 views

Minimal basis CI of H2 dissociation

In Modern Quantum Chemistry by Szabo and Ostlund, they give an example of a minimal basis, full CI calculation of the dissociation of $\ce{H2}$ (on p.$241$ if you have the book). In explaining why ...
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0answers
324 views

Will bonding molecular orbital be formed?

Which of the following statements is not correct regarding bonding molecular orbitals? A Bonding molecular orbitals possess low energy than the atomic orbitals from which they are formed; B ...
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4answers
2k views

MO Theory: Why do hydrogen and lithium bond, but hydrogen and helium don't?

I've been cracking my head trying to make sense of Molecular Orbital Theory, but all sources I find are simplistic {If anyone has an online course or a book to recommend, I'd really appreciate}. ...
14
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1answer
11k views

Molecular orbital diagram for BF3

I'm trying to build a molecular orbital diagram for BF3 and I'm running into problems with irreducible representations on the F side. 2s for B has an irreducible representation of A1. 2p for B has ...
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0answers
448 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) ...
14
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1answer
5k views

Using group theory to make molecular orbital diagrams

Because of Orthocresols' meta post I ask this question about application of group theory to molecular orbital theory. In my undergraduate lecturers, we've seen many examples of making qualitative MO ...
3
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1answer
162 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 $\...
7
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1answer
343 views

Can the idea of entropy be extended to orbitals?

The forward reaction for: $\ce{HF<->H^+ +F^-}$ is entropically favourable; but energetically unfavorable: as there is too much electron density for $\ce{F^-}$ ion to cope up. That's a reason why ...
7
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1answer
793 views

How to explain molecular geometry without the help of VSEPR, valence bond, or hybridization theories?

I was taught, at the high school level, how to rationalise molecular geometries with the help of VSEPR, valence bond, and hybridization theories. However, I have recently also come to know that these ...
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0answers
98 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?
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1answer
519 views

Forming the resonance structures for the nitrite anion

Yesterday I learned about resonance structures and came across this problem. The resonance structures are formed when there is a delocalized π electron cloud. I understand that for benzene, there are ...
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2answers
1k views

Pi molecular orbitals of polyenes

As an organic chemist, I'm comfortable deriving the pi molecular orbitals of linearly conjugate systems to give the following result: In a qualitative sense, these molecular orbitals are easily ...
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0answers
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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0answers
163 views

Intuitively, why is it that when the HOMO-LUMO gap is small then the bonding molecular orbital produced is of significantly lower energy?

What is an intuitive explanation for why a small HOMO-LUMO gap between the electrophilic and nucleophilic species would produce bonding molecular orbitals much lower in energy, giving rise to greater ...
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1answer
896 views

Why does strong Lewis acid-strong Lewis base interactions prevail over hard-soft acid-base interactions?

In Pearson's paper, he mentions that strong acid-strong base interactions are more favourable compared to hard-soft acid-base interactions. He cites the example of $\ce{H+ + H- -> H2}$. In this ...
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2answers
4k views

Is Be2 diamagnetic?

From molecular orbital theory, it has no unpaired electrons but can we conclude it is diamagnetic considering the fact that it does not exist?
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0answers
56 views

Should there be a difference in the absolute energy gaps between bonding and antibonding MOs from the energy level of the AOs in the H2 molecule? [duplicate]

I have been reading Molecular Orbitals and Organic Chemical Reactions (Student Edition) by Ian Fleming. On Pg 5, Fleming mentions that the diatomic helium molecule cannot exists because there is an ...
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1answer
495 views

The MO and unpaired electrons

I am learning molecular orbital in general chemistry. I have come across this question that asks me to show that the Lewis structure of $\ce{O2}$ is actually an excited state when viewed in terms of ...
5
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1answer
777 views

The eigenvector matrix C

I was wondering what the difference between $c_n$ and $c_{jn}$ is? In the context of molecular orbital construction, for example, if $c_{jn}$ is the coefficient of the basis functions $\phi_j$ (...
4
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1answer
430 views

HOMO-LUMO and perturbation theory

I have some confusion about perturbation theory, and just how it fits into the hard-hard/soft-soft interactions within organic reactions. I have come across a formula for perturbation that is ...
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1answer
2k views

Non-bonding molecular orbital in triatomic hydrogen

I am slightly confused about how non-bonding MOs form, for example in H3+ ion as shown below. Why does the central atom not contribute an orbital? The source mentions symmetry, but I can only see ...
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1answer
693 views

Hybridisation and the Schrödinger equation

I am slightly confused about hybridisation and how it relates to molecular and atomic orbitals, despite having pored through many sources online. I was hoping someone could verify whether my current ...
3
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1answer
4k views

Lone pairs in MO theory?

I have learned that non-bonding MOs are lone pairs. However when considering the MO diagram for the $O_2$ molecule, I do not see any non bonding orbitals yet there are two lone pairs on each oxygen ...
4
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1answer
712 views

Jahn-Teller distortion of [Fe(H2O)6]2+

I am wondering whether Fe(II) hydrated to an octahedral complex would undergo a Jahn-Teller distortion. As far as I am aware, this distortion comes about because of asymmetry in filling orbitals, in ...
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0answers
858 views

Why is a CO single bond stronger than a NO single bond?

Why is a CO sigma bond stronger than a NO sigma bond? I would think that since nitrogen and oxygen are of similar size and have similar atomic orbitals (because they are adjacent in the period), their ...
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1answer
525 views

Has it been observed that the dihydrogen molecule dissociates into ions?

As we know from the improved methods valence bond theory (VB), as well as molecular orbital theory (MO-LCAO), the wave function of the $\ce{H2}$ molecule consist of two terms, which belong to covalent ...
5
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1answer
495 views

Why is carbon dioxide bent in its first excited state?

R. H. Crabtree writes in The Organometallic Chemistry of the Transition Metals (p 145, 6th ed.) that $\ce{CO2}$ is linear in the free state but bent [...] in the first excited state... Why is this ...
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2answers
2k views

Cyclobutadiene - Jahn–Teller effect or not?

In transition metal chemistry the Jahn–Teller effect arises when the configuration of the metal ion and d orbital splitting set up a doubly degenerate state, which is less stable than a state without ...
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0answers
536 views

What is the geometry of the intermediate during an SN2 reaction?

Suppose we have 2-bromo butane. The carbon connecting to the bromine will have the following valence electron configuration: $$\underset{2s}{[\uparrow]}\underset{2p}{[\uparrow \vert \uparrow \vert \...
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1answer
90 views

Form of the MOs of butadiene [closed]

We know that in butadiene there are 4 MOs. This is the MO with one node: My question is: Why, with one node, can't we have something like this ?
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1answer
2k views

Is it possible for three carbon double bonds to form next to each other in a carbon chain?

In a typical carbon double bond $sp^2$ hybidrization is used to explain the resulting bond. When two carbon atoms A and B form a double bond one $sp^2$ orbital from A bonds to another $sp^2$ orbital ...
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1answer
1k views

What is the convention on color of molecular orbitals in publication figures?

I'm new to MO-visualization and I'm using the program Orca to generate visualizations of molecular orbitals of a system of interest. I've been able to produce some nice images in VMD but I'm not sure ...
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0answers
155 views

How do we explain shapes of molecules using molecular orbital theory or do we even do that?

How do we explain shapes of molecules using molecular orbital theory or do we even do that ? While reading about the theories to explain chemical combination and stabilities of compounds I read ...
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2answers
514 views

Do chemists use molecular orbital theory to explain physical characteristics of a compound (i.e. melting point, boiling point, etc)

When you think of a molecule as simple as methane CH4, you can see that it has four identical C-H bonds. Carbon has 6 electrons, 2 in 1s, 2 in 2s and 1 in 2px, 1 in 2py and 0 in 2pz. Interestingly, ...
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1answer
414 views

Molecular orbitals of allylic cations, anions and radicals

I was reading the explanations of electronic configurations of the Allylic Radicals, Cations and Anions in my textbook. I completely understand everything, but there is one thing that confuses me. ...
14
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2answers
510 views

After a unitary transformation, is Koopmans' theorem still valid?

Koopmans' theorem says that the energy of the HOMO of the Hartree-Fock orbitals is equal to the first ionization energy of whatever system is being studied. This is only approximate because it assumes ...
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0answers
148 views

Cl-A-Cl bond angle discrepancy

In 2,2-dichloropropane the Cl–C–Cl angle (108.3°) is less than the C–C–C angle (113.0°). In Me$_2$TiCl$_2$, in contrast, the Cl–Ti–Cl angle (116.7°) is larger than the C–Ti–C angle (106.2°). How is ...
24
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1answer
2k views

Canonical MOs vs. Localized MOs: Do both represent reality in the same way?

In my understanding localized molecular orbitals (LMOs) are equivalent to "standard" molecular orbitals, often called canonical orbitals (CMOs—by the way, why are they called canonical?). We can ...
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0answers
69 views

Spatial form of an atom and type of chemical bond

As we know, the first excited states of Hydrogen atoms is $2p$. The wave functions in cartesian basis we can represent as $$ p_x = \frac{1}{\sqrt{2}} \left( Y_{1, +1} + Y_{1, -1}\right) =\...
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1answer
707 views

“NBO diagrams” versus MO diagrams

Molecular orbital diagrams are well known by chemists. According to Wikipedia (emphasis mine), A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining chemical ...
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2answers
287 views

Do MO's span a bond or the whole molecule?

I'm reading Organic Chemistry by David Klein (2nd Ed), and when discussing the causes of torsional strain, he writes this Based on recent quantum mechanical calculations, it is now believed that ...
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0answers
222 views

Why is polyacetylene an insulator?

Recently I have studied Huckel-theory and I appreciated how this approach is suitable to provide simple models to understand chemical behaviour. However, it is highly approximate and qualitative at ...
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0answers
82 views

How do we measure the energies of molecular orbitals? [closed]

This question came on my mind after a sentence of a teacher who said during a lesson: If you imagine hydrofluoric acid, to make the MO's diagram because the energy gap between the $\text{2s}$ of ...
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1answer
254 views

Bonding in MOF-5 [closed]

I came up with this problem today and I can't find the answer elsewhere: How does the oxygen atom bond to the four zinc atoms? To be more specific, what would be the molecular orbital diagram for the ...
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1answer
3k views

Significance of phase of atomic orbitals

I am learning about orbitals and bonding and antibonding MOs. So far, I know that when you combine s orbitals, you form both bonding and antibonding MOs- bonding when the wavefunctions are added in ...
5
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1answer
2k views

Coordination geometry: why is of Cu(acac)2 square planar?

Why is $\ce{Cu(acac)2}$ square planar, whereas $\ce{Al(acac)3}$ and $\ce{Fe(acac)3}$ form octahedral complexes? I see how a similar argument to $\ce{Pt}$ complexes would apply, i.e. with $\mathrm{d^9}$...
14
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1answer
302 views

Help with derivation on why antibonding orbitals are more antibonding

I have read How can antibonding orbitals be more antibonding than bonding orbitals are bonding?. But I am intersted in a specific derivation. During lecture my professor stated that the overlap $S_{ij}...