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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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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42 views

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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50 views

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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32 views

Does overlapping partial density of states indicate formation of chemical bond?

Does overlapping partial density of states of two adjacent atoms indicate formation of chemical bonds between the two atoms? The partial density of states here means the density of states of an ...
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46 views

What is the exact Hamiltonian core of the Fragment Molecular Orbital Method?

My major is not chemistry and I am trying to understand the Hamiltonian core of the Fragment Molecular Orbital (FMO) method. I think it should be the normal Hamiltonian core of the restricted Hartree-...
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71 views

In the LCAO method for $H_2^+$, why do we only add or subtract orbitals but never alter one of the phases of the orbitals?

TLDR: Atkins' physical chemistry contains the quote "In general, from N atomic orbitals we can build N molecular orbitals". In the case of $H^+_2$, we use a combination of N=2 orbitals to ...
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53 views

Molecular orbitals in an ionic diatomic compound

The wavefunction of a heteronuclear diatomic molecule, after the orbital approximation and the Born-Oppenheimer approximation, is $$\psi = c_A \chi_A \pm c_B \chi_B $$ where $\chi$ are the starting AO ...
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63 views

Relation of partial charge with wavefunction

Suppose we have an one electron system. The probability $P$ that electron's position is in some interval $x + dx$ is given by: $$P = \int_x^{x+dx}|Ψ(x)|^2 dx$$ So if we measure $N$ times the electron'...
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Why is the sum of the square of the orbital coefficients 1

I'm reading up on molecular orbital theory and LCAO in Ian Fleming's "Molecular Orbitals and Organic Chemical Reactions" and I don't understand the logic here: "When there are electrons ...
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54 views

Do different types of MOs have different occupancies?

There was a question in my textbook regarding the number of electrons in a molecular orbital. The maximum number of electrons in a sigma, pi, and delta molecular orbital are respectively? Now, I ...
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How to use MO theory for compounds containing 3 atoms?

We have been taught MO theory, and I have learned how to use it for compounds containing 2 atoms. Can we use this theory for compounds like sulphur dioxide, with more than three atoms? If possible, ...
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$\pi$ Molecular orbital diagram of compounds like urea, guanidine, acetone etc

In my organic chemistry course, we've only been taught about how the $\pi$ MO diagrams of compounds like butan-1,3 diene, hexan-1,3,5 triene and similar single chain compounds look like. I was ...
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58 views

C=C and C=O bonds in molecular orbitals

For both $\sigma$ and $\pi$ bonds: A. In terms of electronegativity: Since effective nuclear charge of $\ce{O}$ is higher than $\ce{C}$, so the E.N. of $\ce{O}$ is higher than $\ce{C}$. Therefore, ...
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Does (BeCl2)n have 3c - 4e- bonding or not?

The title really explains what the issue is here. I would think that it has multicenter bonding akin to $(\ce{BeH2})_n$ polymer because they are pretty much iso-structural (although it shouldn't have $...
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54 views

How can 2 molecular orbitals form simultaneously? [duplicate]

I understand (for example in the case of H2) that two s orbitals produce through constructive interference a bonding orbital and that the out of phase combination of two s orbitals leads to ...
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245 views

Is strength of pi bonds greater than sigma bond of nitrogen molecule?

I am referring to molecular orbital (MO) theory. In the nitrogen molecule (and elements of lower atomic number) $\textrm{sp}$ mixing occurs and the sigma orbital set is raised above the pi orbital set....
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49 views

Computational determination of the diagram of molecular orbitals of a polyatomic chemical species

A diagram of molecular orbitals for $\ce{H2O}$ would be as follows: The above diagram has been constructed qualitatively following the steps that I have been instructed in various classes on this ...
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56 views

Question regarding conflicting results of checking the electron-preciseness of isoelectronic species via NBO and EHM calculations

It is well known that the tert-butyl cation's empty 2p orbital on the central carbon is stabilised by hyperconjugation from neighboring C-H bonds. This would mean that the central 2p "lone pair&...
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1answer
182 views

What is the correct molecular orbital diagram for the d orbitals in platinum for the tetraammineplatinum(II) complex?

I am trying to construct the diagram of $\mathrm{d}$ orbitals in the tetraammineplatinum(II) complex. According to the angular overlap model, $\mathrm{d}$ orbitals are going to look like those in the ...
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70 views

Molecular orbitals energy under pressure

Suppose we have a hydrogen molecule $\ce{H2}.$ At room temperature the average distance of the nuclei is $r_0$ (without applying pressure). If we put $n$ hydrogen molecules in a box with volume $V_\...
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Construction of the molecular orbital diagram for a species M4

I need to construct the molecular orbital diagram for the hypothetical species ${Li_4}$, which has the following geometrical arrangement: The first step is to identify the point symmetry group. In ...
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1answer
59 views

Why d and s orbitals overlap even when there is considerable difference in their energies?

In my grade 11 chemistry NCERT textbook, its written that hybridization happens when orbitals of almost same energy overlaps. But S orbital and D orbital have significant difference in their energies. ...
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First ionization energy and electron gain enthalpy of dihydrogen / stability comparison of dihydrogen ions [duplicate]

Subset of: How can antibonding orbitals be more antibonding than bonding orbitals are bonding? Stability of $\ce{H2^{-}}<\ce{H2^{+}}<\ce{H2}$ Stability of $\ce{N2^{-}}<\ce{N2^{+}}<\ce{N2}...
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How can orbitals of Hydrogen and Chlorine atom combine to form molecular orbitals of Hydrogen Chloride? [closed]

Linear combination of atomic orbitals (LCAO) states that orbitals can only combine if the energies and shape of the orbitals are same. $3p$ orbital of Chlorine and $1s$ orbital of Hydrogen are the ...
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32 views

Spin Multiplicities of Ions

The multiplicity is fundamentally defined as $2S + 1$ where $S$ is the total spin. From what I understand, the multiplicity corresponds with the number of unpaired/paired electrons. For example, in ...
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molecular orbital theory and crystal field theory confusions

I am a high school student and I am very confused in Molecular orbital theory, it says that when two orbitals overlaps in the same phase, they form antibonding orbitals and when they overlap in ...
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100 views

Explanation of the trans-effect (thermodynamic and kinetic) for octahedral transition metal complexes

The thermodynamic trans effect refers to the ground state weakening of the metal-ligand bond in a complex by a ligand trans to it. The kinetic trans effect is the lablisation of a ligand in a complex ...
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1answer
83 views

What is the LUMO of a molecule with an alkene and a carbonyl?

In a molecule that has both an alkene (C=C) and carbonyl (C=O) that are NOT conjugated, such as pent-4-en-2-one, how do you determine which π* anti-bonding orbital is the LUMO? Essentially, I'm trying ...
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28 views

Is an element's "atomic electron configuration" EXACTLY equal to the term with the largest coefficient in the CI series of the neutral atom?

For atoms and molecules with more than one electron, the wavefunction cannot be written as a single Slater determinant, so the ground-state configuration of (the atom or molecule in question) is ...
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760 views

How do atomic orbitals interfere both constructively AND destructively to give two molecular orbitals?

I am an organic chemistry student learning how atomic orbitals interfere to give rise to molecular obitals. The image below suggests that each of the hydrogens' atomic orbitals interfere both ...
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1answer
330 views

Why is a sodium chloride molecule stable?

The ionization energy of sodium is $\pu{5.139eV}$. This is the energy absorbed when a neutral sodium atom is stripped of its outermost electron. The electron affinity of chlorine is $\pu{3.62eV}$. ...
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Relation between the number of hybridised orbitals and the number of sigma bonds

March's Advanced Organic Chemistry (8th Ed.), has in its first chapter several tantalizing statements of the following variety; Boron has only three valence electrons available to form bonds, hence ...
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35 views

A contradiction in the nucleophilic attack of hydride ion based on charge densities

On page 130 of Organic Chemistry by Clayden, it is stated that Nucleophilic attack by the hydride ion, $\ce{H-}$, is an almost unknown reaction. This species, which is present in the salt sodium ...
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Orbital Interaction for electrophile and nucleophile

Clearly, the above diagrams depict the interaction between empty orbital of electrophile with filled orbital of nucleophile. We may assume that the HOMO of nucleophile being more electronegative will ...
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1answer
32 views

Why does STED microscopy cause photodamage?

STED (stimulated emission depletion) microscopy is a technique which enables sub-diffraction limit of light imaging. The depletion laser is at 775nm, and about 500 mW, concentrated for a short ...
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47 views

What makes up the conduction band?

Prologue/Rant about online classes We have been taught the electron sea model to explain metallic bonding and conduction of electricity by metals. Then out of the blue, the band theory was introduced, ...
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70 views

Molecular Orbital Diagram

Chemists have revealed that $1 \lambda^{2}, 2 \lambda^{2}$ -disilene $\left(\mathrm{Si}_{2}\right)$ is diamagnetic while disulfur $\left(\mathrm{S}_{2}\right)$ is paramagnetic $(\mathrm{S}=1)$. Draw ...
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93 views

D-orbitals of point group C2v

I'm trying to construct an MO diagram for cisplatin, which has C2v symmetry. However, there is no Mulliken label for the d(x^2-y^2) orbital in the character table. Does this orbital not form molecular ...
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49 views

Can atomic orbitals combine in a manner intermediate between bonding and antibonding?

When atomic orbitals combine in phase (0°) we get bonding molecular orbitals, and when they combine with opposite phases (180°) we get antibonding molecular orbitals. Why can't atomic orbitals combine ...
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41 views

Why does dilithium have a longer bond length than dihydrogen?

I've tried MO theory however they both have a bond order of 1. Which means we can not relate the bond order to the bond length. My thinking - I think that the h2 bond length is shorter due to only ...
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66 views

TD-DFT transition dipole moment vector does not align with experimental data

I have been modelling excited states of some molecules with similar stucture using TD-DFT theory, however, I have encountered an issue that sometimes transition dipole moment does not align with the ...
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49 views

What does Molecular Orbital Theory allow you to predict?

Molecular Orbital theory reveals the outcome when two atomic orbitals overlap. Almost all of the time we draw a Y axis with the notation of energy that can be described using electron volt units (eV). ...
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1answer
79 views

Why are steric effects repulsive?

Normally, I think about orbitals interacting in the context of bonding. When two atomic orbitals overlap, they can do so in-phase or out-of-phase. The in-phase overlap results in a bonding molecular ...
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Interpreting data on molecular orbitals in GaussView 6.0 [duplicate]

Introduction I have been trying to use computational software to gain more insight into how molecular orbitals are formed, as well as their shapes and sizes in accordance with Molecular Orbital Theory....
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38 views

Diatomic molecule under pressure

If we put a diatomic molecule under pressure the interatomic distance will be decreased and according to this graph the potential energy of the bonding molecular orbital will be increased. What will ...
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79 views

Confusion regarding orbital, electron and Quantum no’s [closed]

Now , In some textbook I have read that orbital is nothing but the shape of electron . s,p,d orbitals etc. So , after knowing shape of an orbital . I got to know that inside the orbital is an electron ...
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68 views

What are "Secondary Orbital Interactions" in Organic Chemistry? [closed]

We used these to analyze the stability of molecules in an Organic Chemistry Course. My teacher analyses the stability of compounds on 3 levels: Atom level by studying the hybridization of the main ...
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1answer
136 views

Comparing O−O bond length in hydrogen peroxide and dioxide(2−) ion

Problem How can we qualitatively compare the bond lengths between $\ce{H2O2}$ and $\ce{O2^2-}?$ Answer Attempt I tried using molecular orbital theory, but since both have peroxide $\ce{O2^2-},$ the ...

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