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.

Filter by
Sorted by
Tagged with
0 votes
0 answers
32 views

Information on 'charge shift' bonding in oxygen molecules?

I would need information on the charge shift bond regarding dioxygenyl O2+ Triplet oxygen O2 Hyperoxide O2- Peroxide O2-- Concerning O2, I have already found a couple of articles that classify ...
1 vote
0 answers
9 views

MOLPRO: is there an analogue of the Gaussian FCHK file? [migrated]

With the Gaussian quantum chemistry program, I usually generate formatted checkpoint files (.fchk) that I then use to perform different atom-in-molecule analyses. I am currently facing the need of ...
  • 341
-3 votes
0 answers
30 views

how use Molecular orbital symmetry to reduce computing amount in multi-reference method(like full CI)?

I know every molecular orbital possess a symmetry and belongs to an irreducible represention. And it seems we can use this symmetry to reduce computing amount in multi-reference method. Say in full CI,...
0 votes
0 answers
42 views

Energy of a molecule using MOs diagram (case of CH4)

I'm trying to find the ground state energy of CH4 in order to compare it with simulations I made. I came across this diagram of energy (not sure it gives the true energies though, if you could confirm....
2 votes
0 answers
29 views

Molecular Basis set construction (STO-3G) for BeH2 [migrated]

I have a rather basic question about the (minimal) number of molecular orbitals that are needed for some computation work on the BeH2 molecule. To my understanding, STO-3G forms a minimal basis set, ...
2 votes
1 answer
97 views

Is there a difference between Hartree-Fock method and LCAO?

I have to dive in some quantum chemistry for a quantum machine learning project and I came across the so-called Hartree-Fock method. In one of the reference I used, they considered electrons as ...
0 votes
0 answers
21 views

What are the highest and lowest (un)occupied molecular orbitals in this nucleophilic reaction?

I need to find the highest occupied molecular orbital and lowest unoccupied molecular orbital for this reaction. I'm not really sure where to start. I think it might be an SN2 reaction but I don't ...
  • 21
0 votes
1 answer
82 views

Role of spin of electron in splitting of orbitals

What will happen if there are electrons with opposite spins present in the orbitals of ligand and metal atom during the splitting of orbitals in crystal field splitting? Magnetic fields of two ...
1 vote
1 answer
131 views

Lewis structure of XeF2 that comes closer to reality?

Meanwhile, the hypervalency of Xe in XeF2 is explained by the 3c4e bond, where the p orbitals of the 3 atoms overlap to form a delocalized system of 3 MO's in which 4 electrons (two from the Xe p ...
3 votes
0 answers
84 views

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 ...
0 votes
1 answer
218 views

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?...
user avatar
2 votes
0 answers
58 views

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(...
1 vote
0 answers
41 views

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 ...
  • 11
4 votes
1 answer
181 views

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 ...
  • 43
-2 votes
1 answer
43 views

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?
  • 196
0 votes
0 answers
77 views

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_{\...
2 votes
0 answers
24 views

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 ...
  • 184
1 vote
1 answer
67 views

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 ...
  • 119
0 votes
0 answers
87 views

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 ...
  • 101
0 votes
0 answers
29 views

Quadruple. quintuple and sextuple bonds [duplicate]

I am a highschool student and till now i thought 3 bonds was the limit, however yesterday i came across [Re2Cl8] which has a quadruple bond between the two rhenium atoms. when i further dug into this, ...
1 vote
0 answers
26 views

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 ...
  • 333
2 votes
0 answers
43 views

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/...
  • 21
0 votes
1 answer
62 views

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 ...
0 votes
2 answers
103 views

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?
  • 15
10 votes
2 answers
340 views

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 ...
6 votes
2 answers
149 views

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 $m/z = 16$ ...
  • 91
0 votes
0 answers
44 views

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 ...
  • 321
1 vote
2 answers
108 views

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^...
  • 321
0 votes
0 answers
23 views

Origin of triple state orbital energy degeneracy difference between restricted open-shell Hartree-Fock and standard HF?

I am wondering why I only observe orbital degeneracies for molecular systems that exhibit degeneracies when I run a restricted open-shell Hartree-Fock calculation (ROHF) on the triplet of the system, ...
0 votes
0 answers
18 views

Are the energy differences between corresponding bonding and anti bonding molecular orbitals equal? [duplicate]

Are the energy differences ΔE₁ and ΔE₂ equal in a molecular orbital diagram? I learned molecular orbital theory from two teachers. One of them taught me that the energy differences will be equal, ...
  • 284
0 votes
0 answers
45 views

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 ...
  • 73
0 votes
0 answers
37 views

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) &...
  • 5
0 votes
0 answers
55 views

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 ...
2 votes
0 answers
32 views

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],...
  • 181
7 votes
1 answer
1k views

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 ...
  • 1,596
4 votes
1 answer
95 views

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 (...
  • 69
3 votes
1 answer
335 views

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 ...
2 votes
1 answer
217 views

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 ...
0 votes
0 answers
28 views

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. ...
-1 votes
1 answer
303 views

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:)
8 votes
0 answers
201 views

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
0 votes
0 answers
123 views

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. ...
7 votes
1 answer
140 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 ...
  • 883
5 votes
1 answer
648 views

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. ...
7 votes
4 answers
436 views

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/...
4 votes
1 answer
183 views

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 ...
  • 145
1 vote
0 answers
797 views

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 ...
  • 147
1 vote
1 answer
375 views

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 ...
  • 126
4 votes
0 answers
101 views

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
2 votes
2 answers
157 views

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 ...
  • 137

1
2 3 4 5
15