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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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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 ...
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Would a hypothetical Og2 +235 form a chemical bond?

In a hypothetical (?) Og2+235 we would have a simple sigma bonding orbital occupied by one electron (leading to a bond order of 1/2). But how to take into account the giant repulsion of the two nuclei?...
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Why is the imine (C=N) bond so weak?

Nitrogen is similar to carbon in terms of electronegativity and size. MO theory suggests that the more electronegative N would result in a lowering of the of the π-bonding energy, E(πCN), below the E(...
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Reproducing Hydrogen Molecule Hamiltonian in OpenFermion

I am learning quantum chemistry at the moment and I'm trying to understand the Hamiltonian generated by the OpenFermion package. I'm now stuck at understanding how openfermion calculates the ...
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Self Consistent Field method and LCAO

I am reading about the Self Consistent Field Method and Linear Combination of Atomic Orbitals. Suppose we have one electron and one nucleus, then we can solve the Schrodinger equation explicitly. If ...
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Variation in the energy of the $\ce{\sigma_{2pz}}$ orbital

Is there a specific reason why the energy of the $\ce{\sigma_{2pz}}$ orbital varies relative to the $\ce{\pi_{2px}}$ and $\ce{\pi_{2py}}$ orbitals, depending on the atomic number of the atom?
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How to determine the characters of px atomic orbital in C4v point group?

How to determine the characters of px atomic orbital in $\text{C}_{\text{4v}}$ point group? I understand (px,py) is a set of basis function of E, and px and py are mixed by $\text{C}_4$ and $\sigma_{\...
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LCAO-MO ansatz for arbitrary hydrogenic molecule term

I am struggling to understand the connection between molecular electronic term symbols and translating the symmetries to the underlying wavefunction. In particular, my understanding of the LCAO-MO ...
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On the energies of molecular orbitals

I found a useful (though simplified) scheme illustrating the energies of atomic orbitals, in crescent order: I wonder if there was an analogous (simplified) scheme or rule for molecular orbitals, at ...
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sp mixing in $N_2$ vs sp mixing in CO

We were first taught that in B, C and N the bonding $\sigma_{2s}$ orbital repels with the bonding $\sigma_{2p}$ orbital which cause the energy level of $\sigma_{2p}$ orbital to increase. This increase ...
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Is there a molecular orbital equivalent of rehybridization?

I generally have seen the pyramidal inversion of NH3 explained in terms of rehybridization. The sp3 hybridized NH3 changes to sp2, with the lone pair in the p orbital, and then reverts to sp3 in the ...
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Hartree Fock calculations on F2 don't match the traditionally taught MO diagram

I ran some Hartree-Fock calculations on F2 to visualize the MOs, and the energy levels don't match the trend commonly taught (shown here: https://chem.libretexts.org/Courses/...
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Shouldn't the negative charge be on carbon in this scenario according to molecular orbital theory [closed]

I am sorry in advance for posting an image in this question. I know it makes searchability difficult, but I don't see any other way The above screenshot is from Claydens organic chemistry. We can see ...
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Molecular orbital mixing in second period elements

Why do the $\pi_u(2p)$ and $\sigma_g(2p)$ diatomic MO mix within the second period elements as it's shown in the image below?
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Bonding in hypervalent molecules

I don't know where they go the electrons of the extended-valence in molecules like $\ce{SF6}$ or $\ce{PCl5}$ for instance because my teacher said that the d orbitals can't interact with s and p (or ...
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Does the MS oxygen peak at m/z = 16 correspond to $\ce{O+}$ or $\ce{O2^{2+}}$?

In a mass spectrum, while annealing with $\ce{O2}$ of a sample in UHV, I observe peaks at $m/z = 16$ and $32 (= 16 \times 2)$. While the latter is $\ce{O2^+}$, I'm unsure what the peak at $m/z = 16$ ...
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What does "shape of hybrid orbitals" mean?

My teacher and textbook distinguish between the $sp$,$sp^2$ and $sp^3$ hybrid orbitals' shapes by saying that the first has linear shape, the second has trigonal shape, and the third has tetrahedral ...
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Why are there FOUR $sp^3$ hybridized orbitals in methane?

(This may be a stupid question, but I've only learnt about hybridization yesterday.) I will take the example of methane. The valence shell electron configuration of ground state of carbon is $2s^2 2p^...
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Do diatomic isoelectronic molecules have the same bond order even when the octet rule is not followed?

It can be observed and proven that diatomic isoelectronic molecules have the same bond order when they follow the octet rule (upto 3rd period elements). But what about when they do not follow the ...
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What is the energy ordering of molecular orbitals in diatomic molecules of third and fourth period elements?

For diatomic molecules with less than 16 electrons, the list of molecular orbitals in order of increasing energy is: σ1s < σ*1s < σ2s < σ*2s < (π2py = π2pz) < σ2px < (π*2py = π*2pz) &...
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Orbitals in benzene and other delocalised structures

I've read that molecular orbital theory demands that if there are $n$ orbitals prior to some event like bond formation, there should be $n$ orbitals after this event. Does this hold even in structures ...
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How do the spin-matrices change in systems without spherical symmetry?

The (non-relativistic) spin matrices of a free electron, with $z$ as the quantization axis, read: $$ \boldsymbol{S}_{x}=\frac{\hbar}{2}\left[\begin{array}{ll} 0 & 1 \\ 1 & 0 \end{array}\right],...
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What theory accurately explains metallic bonding in beryllium?

Since beryllium is an alkaline earth metal, the bonds between beryllium atoms could be considered metallic and we can use molecular orbital theory (MOT) to explain metallic bonds in metals. Consider ...
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pKa of methylene protons in cycloheptatriene vs cyclopropene

The $\mathrm{p}K_\mathrm{a}$ values of methylene protons in cycloheptatriene vs cyclopropene are found to be 60 and 36, respectively. From what I understand - both conjugate bases are non-aromatic (...
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Why is this diagram depicting the molecular orbital (MO) basis for a back-side attack the way it is?

Consider: The description of this image in my textbook is as follows: In order to form a bond, the HOMO (the highest occupied molecular orbital) of one species must interact with the LUMO (the ...
Nick Bauer's user avatar
2 votes
1 answer
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Explanation of the missing 1-s orbital electrons of carbon in the molecular orbital diagram of methane

Consider the molecular orbital diagram of methane, for example found here: I would like to know what happens with the two 1s orbital electrons of carbon in the molecular orbitals it is forming. Is it ...
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Crystal Field Splitting Energy - Tetrachlorocuprate and Tetrachlorocobaltate

I'm a high schooler from India and it's my first time on this stack exchange. I was wondering why the crystal field splitting energy of tetrachlorocuprate differs so much from tetrachlorocobaltate. ...
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Why are the 1s bonding and antibonding molecular orbitals excluded while making Molecular Orbital diagram for diatomic homo/heteroatomic molecules?

Do these molecular orbitals not form or are they left out as something general that doesn't require repeated mentioning? I'm in my first semester of college so please keep the explanation simple:)
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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 ...
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Molecular orbital theory and Lewis structure for dioxygen

I am a bit confused about how molecular bond theory predicts pairings of unbounded electrons. For example, in $\ce{O2}$ there are two pairs of electrons on each oxygen along with the double bond. ...
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1 answer
318 views

How does the MO-LCAO theory explain the direction of valence bonds?

As all the bells sound, the common explanation of geometry of a molecule (consider the water molecule) is due to overlaping electron density. The valence bond theory of the water molecule describes ...
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How can I use the MO diagram of hydrogen fluoride to demonstrate that the molecule is polar?

I am trying to explain that HF is a polar molecule using the MO diagram. Normally I say that the F atom has a higher electronegativity than the H atom, which causes a net positive dipole moment. ...
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7 votes
4 answers
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When pigments absorb light only around a single particular wavelength, why aren't they still white?

I'm trying to understand how organic molecules get their colour. One major factor are conjugated double bonds which create delocalized pi-orbitals (e.g. https://en.wikipedia.org/wiki/...
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1 answer
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Can two noble gases attract each other?

If two hydrogen atoms are far apart, they have no effect on one another. But as they are bought closer together, they begin to excerpt an effect. The two nuclei, having the same positive charge, repel ...
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What is the LUMO and HOMO in and O2 diatomic

In the molecular orbital (MO) diagram for the $O_2$ diatomic, the $2π_g^*$ contains two unpaired electrons. This is certainly the HOMO, as it is the highest molecular orbital with electrons. My ...
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Why are anti bonding orbitals distorted towards the less electronegative element?

Bonding molecular orbitals are distorted towards the more electronegative atom and so the atomic orbitals from this atom contribute more to those bonding orbitals. This implies that anti bonding ...
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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 ...
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Determination of energies in MO diagrams

How do we determine the relative placements of molecular orbitals in their diagrams? I understand that we can use point groups to find symmetry-allowed interactions between orbitals that we write on ...
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1 answer
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Contribution, and the way thereof, of the core 6p orbitals of compounds of plutonium(VIII)

According to the NIST database, the ground-state configuration of plutonium(VIII) is [Hg]5f³6p³, when intuitively it should be the same as neutral radon([Hg]6p⁶). Since plutonium(VIII) compounds are ...
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1 vote
1 answer
487 views

What does it mean for an electron to be in a bonding/antibonding orbital?

My confusion arises from the fact that bonding and antibonding orbitals are created simultaneously. I have read this answer that clarifies about the existence of the molecular orbitals itself. But now ...
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How are the energies of natural atomic orbitals calculated when they are, strictly speaking, not "meaningful" wavefunctions?

There are several programs that can calculate the "energies" of the natural atomic orbitals(NAO) that come from NBO analysis. However, I have several evidence that, unlike the energies of ...
Kanghun Kim's user avatar
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Why SCF procedure in Hartree-Fock doesn't keep returning the same coefficients?

In the context of Hartree-Fock theory, using Roothaan formalism, we write: FC=SCE where F is the matrix of the Fock operator, C are the coefficients to be used in the construction of the wave function ...
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Justification for using valence bond theory and molecular orbital theory together?

Elementary gen chem books will make the careful distinction between the two theories and then proceed to claim that chemists can use both to complement each other to explain the behavior of certain ...
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1 answer
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How can Phthalocyanine be aromatic when it is not planar? [closed]

Even as Hückel's rule is not applicable in every scenario, especially in metallic clusters, it seems that organic structure need to be planar to show aromaticity. That being the case, Pubchem's ...
C-Consciousness's user avatar
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1 answer
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Which ion has a greater paramagnetic property?

I just recently began studying the Molecular Orbital Theory in Chemistry and I just learnt about the paramagnetic and diamagnetic nature of molecules based on their unfilled and filled orbitals. Now ...
noob anomaly's user avatar
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Why are HOMO and LUMO energies invariant under spin-flip?

Atomic theory says singlet and triplet energies for the same orbital differ because of exchange interaction. However, molecular orbital (MO) theory describes the energy between the HOMO (highest ...
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Does the 1s orbital have two different phases? [duplicate]

How can the 1s orbital (in H atom for example) interfere both constructively and destructively (to give rise to bonding and antibonding molecular orbitals) with another 1s orbital, if the 1s orbital ...
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For benzene, why are the first three pi molecular orbitals considered bonding, and the higher three antibonding?

Is it because all the molecular orbitals that are naturally occupied are all considered to be bonding orbitals? So for benzene, since the lowest three orbitals are all occupied (due to benzene having ...
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Why does the same type of hybridization appear in both Valence Bond Theory and Molecular Orbital Theory?

I was reading about Molecular Orbital Theory, and saw that you can treat a central atom's atomic orbitals as hybrid orbitals in order to simplify the process of creating molecular orbitals by no ...
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Why exactly is the conduction band in semiconductors conducting?

Is it because when the electrons are excited to a higher energy level, they can lose energy and fall back down to lower energy levels? Due to the sheer number of antibonding MOs in the conduction band,...
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