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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81 views

What is the shape of [Cr(NO)₄]?

I was learning about crystal field theory recently. I am quite confused about predicting the shape of $\ce{[Cr(NO)4]}$ complex because I am not able to conclude whether it will be square planar or ...
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C2 molecule has two pi bonds but such a thing is not observed in O2 molecule

As per molecular orbital theory, the electronic configuration on $\ce{C2}$ molecule is:- $\ce{σ_{1s}^2 σ^*_{1s}^2 σ_{2s}^2 σ^*_{2s}^2 (π_{2p_x}^2=π_{2p_y}^2)}$ here, the last four electrons which are ...
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Oxygen analogue of benzene [duplicate]

Cyclic ozone is theoretically possible although it has been found in some cases, so is a six-membered oxygen ring (oxygen analogue of benzene) theoretically possible too?
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Can one describe the bonding of Na to F in terms of molecular orbital theory? What about valence bond theory?

I would kindly appreciate an explanation in terms of the two accepted quantum mechanical theories -valence bond & molecular orbitals- for the electronic energy level structure in natrium fluoride $...
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The molecular diagram of the Boron hydrogen bond (B-H)

In class today, we had a discussion about the bond between boron and hydrogen and we drew it like this(The pictures on the right are the corresponding molecular orbitals): The argument was that 2s ...
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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 ...
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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, ...
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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 ...
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What is the maximum number of hybrid orbitals an atom can have? [closed]

What is the maximum number of hybrid orbitals and atom can have? It is usually seen that an atom does not have more than 6 hybrid orbitals. Why is it so?
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Do SALC-AOs really belong to their symmetry species?

I'm working through a molecular symmetry textbook and something keeps nagging at me. If I derive the SALC-AOs for NH3 (using the projection operator method), I'll get A1: $ \frac{1}{\sqrt{3}}(\...
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Overlap integrals in Hückel theory

In Hückel theory we are only interested in π systems, where $\mathrm p_z$ orbitals overlap. One of the approximations in Hückel theory is that the overlapping $\mathrm p_z$ orbitals are orthonormal: $...
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How do we obtain the π molecular orbitals for allene via Hückel theory?

For a conjugated system, for instance 1,3-butadiene, we can try to obtain the π molecular orbital energies and wavefunctions via Hückel theory. In our given molecule, there are 4 interacting Pz ...
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Focusing on HOMO when discussing thermal electrocyclic reactions

When taking into consideration the outcome of a thermal electrocyclic reaction, why do we focus specifically on the HOMO of the conjugated polyene? Why does it seemingly have the highest contribution ...
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Precise definition of cylindrically symmetry in MO theory?

I was watching an MIT OpenCourseWare lecture on MO theory which mentioned that $\sigma$ orbitals are "cylindrically symmetrical." I was a bit confused, because I was under the assumption that the ...
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Computing energy of Guassian basis set

Actually, I'd like to compute decay rate using : $$ \Gamma = 2\pi \ | \langle ab|V|cd \rangle|^2 \delta\ (\epsilon_f-\epsilon_i) $$ where a, b, c, d are the MOs and V is coulomb interaction, and $\...
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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?
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Breaking bonds with magnetic fields

I was wondering if we could break a bond by applying a big magnetic field on a molecule. The magnetic would just cause the spin of cores of the atoms making the molecule to be aligned , raising the ...
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1answer
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Why does a bonding molecular orbtial increase stability? [duplicate]

When two atomic orbitals come together, they fuse to form a molecular orbital. There is a large probability that the electrons will spend time between the nuclei. This will reduce the nuclei - nuclei ...
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1answer
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Connection between irreducible representations and electronic states in diatomic molecules

I am trying to understand the connection between irreducible representations and molecular electronic states. To explain the problem: I found some potential energy curves (PECs) for $\ce{N2+}$ in the ...
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107 views

How are molecular orbitals obtained in quantum chemistry?

When trying to solve for a molecule's molecular orbitals, we start off with the total molecular hamiltonian. However, given the difficulty of solving the Schrödinger Equation for this complicated ...
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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 ...
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1answer
46 views

Molecular antibonding orbitals energy

When we heat hydrogen the energy of the molecular orbital of H2(1s) is increased .What happens to the energy of the antibonding molecular energy of hydrogen(1s*)?
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Projection Operator Method on Cl4+

I am not quite sure how to start on 1b.We are given 2 diagrams but I am not sure how to use the second one in the question, or if we have to. I got the point group for Cl4+ to be (D2h) however, but ...
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Does the hybridization of sp3d2 type exist?

Is the hybridization of $\ce{XeOF4}$ $\mathrm{sp^2}$ rather than $\mathrm{sp^3d^2}$, because the latter type of hybridization does not exist? Every answer in the Quora thread "How can we find the ...
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Why is the carbon monoxide triple bond stronger than the nitrogen-nitrogen triple bond?

The $CO$ triple bond has a bond enthalpy of 1072 kJ/mol while the $N_2$ triple bond has a bond enthalpy of 945 kJ/mol, at least according to my source. The molecules are isoelectronic, so I couldn't ...
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Why is the top SN2 reaction faster? (Molecular Orbital Theory)

I'm having trouble understanding why the top SN2 reaction proceeds faster. I know that benzylic and allylic halides react faster in SN2 reactions than non-conjugated halides. I think it's because the ...
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How can ionic bonding in lanthanides occur without valence orbitals available for overlap?

I've recently been taught that the 4f orbitals in lanthanides are "core-like", supposedly meaning they have radius smaller than the 4d orbitals, therefore they are not available on the outside of the ...
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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 ...
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What can we learn from the energies of molecular orbitals?

Molecular orbital theory is successful in calculating the structure of molecules (minimizing the total energy with respect to atomic positions). The solutions of an MO calculation are useful in ...
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CO2 dynamics-vector correlations [closed]

I would like to ask if anyone has any information (schematic diagram)of vector correlations for CO2 molecule. (Is it bending in the excited state with μ in plane? How CO fragment can be ejected after ...
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1answer
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For molecular orbitals, how is an energy of zero set or defined?

When labeling the energies of molecular orbitals, often some anti-bonding MOs are shown with a positive energy. For example, MolCalc has the following energies for methane (the anti-bonding MO #8 at +...
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Why does ψ^2 ( square of orbital wave function ψ) give the probability of an electron in a given region? [duplicate]

Today I was introduced to the Orbital Wave Function for electrons. $\Psi$ is a mathematical function for coordinate of electrons and has no physical meaning. But $\Psi^2$ gives probability of an ...
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320 views

Electron pairing in atoms

A question asks: This question refers to isolated gaseous atoms. In which atom are all electrons paired? Ba, Br, S or Si? I thought it was Ba as its electron configuration is [Xe] 6s2. However, ...
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Why does the binding of DMSO to metal via the S atom (k-S) strengthens the S=O bond?

So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\mathrm{\kappa O}$ and $\mathrm{\kappa S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given ...
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MO analysis of a radical reaction of chlorine radical with methyl radical

Im trying to create an MO energy diagram for the reaction of a chlorine radical with a methyl radical by creating the 5 group orbitals for methyl radical(with pyramidal geometry) and then creating ...
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Does the number of bonding MOs always equal the number of antibonding MOs

In (I think all) of the molecular orbital (MO) diagrams I have seen, I have observed that the number of antibonding molecular orbitals is the same as the number of bonding molecular orbitals. Here ...
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Why is the HOMO-LUMO gap in N2 and CO of different sizes? [closed]

Why is the HOMO-LUMO gap in $\ce{N2}$ and $\ce{CO}$ different even though they have the same number of valence electrons?
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How many π-electrons are there in 2-methylene-2H-pyran?

I thought that the structure will be aromatic and stabilised because one of the lone pairs being delocalised with the help of conjugated double bond system but still only 3 π-bonds will be present at ...
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Geometry of Ni(acac)2

The complex $\ce{Ni(acac)2}$ is paramagnetic as expected , i.e it has two unpaired electrons giving rise to a magnetic moment of $ \sqrt{8}$ BM but doesn't have the tetrahedral geometry consistent ...
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1answer
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Mathematical equivalence of ionic-bond resonance structures and d-orbital participation in hypervalent molecules

It is now routine in the scientific community that "main-group hypervalent molecules, under certain conditions, tend to be better represented by resonance structures involving ionic bonds, rather than ...
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How to perform Mulliken population analysis by hand with GAMESS output?

I did a simple calculation on hydrogen fluoride with GAMESS and I wanted to reproduce the Mulliken population analysis for atomic orbitals. A molecular orbital is a linear combination of atomic ...
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pi-type bonding interaction along the bond

I was given the diagram of $\ce{BF3}$'s LUMO and asked to assess its bonding character as shown below: Below is the model answer for the annotated version. I managed to correctly answer the HOMO MO ...
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Molecular orbital diagram of hydroxide ion?

I would like to understand how to create a molecular orbital diagram for the hydroxide ion from scratch. This includes understanding the shape of the molecular orbital. Here is an attempt I have come ...
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Books for organic chemistry [duplicate]

What is the best book to start organic chemistry once I know the basic knowledge of reaction mechanisms like substitutions (nucleophilic, electrophilic and some basic other mechanisms that are given ...
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Symmetry of an FO

I want to ask a question about the symmetry of an FO for $\ce{[CuL2]^-}$ where L is a $1e^-$ donor sigma bonding ligand (e.g. Me). For the ligand orbitals, I produced the following orbitals shown ...
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Questions in MO theory

Τhe electrons in the antibonding MO are the unpaired electrons of the molecule? E.g. $\ce{O2}$, by writing down the diagram for the MO we notice that there are only 2 electrons in the top antibonding ...
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How to understand the (non-)degeneracy of states of singlet Σ and Δ terms for a ππ configuration of two nonequivalent electrons?

As instructed in Levine's Quantum Chemistry 7th edition, Chapter 13.8, page 377, for a $\pi \pi$ configuration of two nonequivalent electrons, four functions $\pi_{+1}(1) \pi_{-1}^{\prime}(2)$, $\pi_{+...
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Energy Levels of Molecular Orbitals formed by combination of Atomic Orbitals

In general when we talk about chemical bonding, we say that it is "nature's way to stabilize the systems" and the energy of the molecule formed by atoms will be lower than that of the individual atoms;...
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Effective Bohr Radius in Transition Metal Complexes?

I am playing around with a toy model of a transition metal complex where the HOMO are $d$-electron states of predominantly transition metal character. Let's say this is a $d^1$ (or $d^9$) system and ...

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