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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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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139 views

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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18 views

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 does conjugation increase the stability of a compound [closed]

I have read that the stability of a compound is increased by conjugation, which allows electrons to delocalise and thus be more spread around the molecule. I'm struggling to understand how this ...
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1answer
56 views

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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19 views

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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75 views

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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19 views

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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1answer
45 views

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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59 views

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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Energy diagram of copper iodide complex

We did an experiment where copper iodide 4-methylpyridine and copper iodide imidazole was formed and now we are asked what orbital the electron is excited from and to. After much research we still ...
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118 views

Hybrid orbitals, photoionization and time dependence

Wikipedia, in the article on Orbital Hybridisation, states the following: One misconception concerning orbital hybridisation is that it incorrectly predicts the ultraviolet photoelectron spectra of ...
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Question about d-orbitals [closed]

I saw somewhere that, "in PF5, the 3d orbitals of phosphorus end up in the anti-bonding molecular orbitals, and thus contribute less to the final molecule" and that "the hypervalency of some ...
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300 views

Question about the role of d-orbitals in polarisation

I know that, although many elementary books say that d-orbitals are involved in the bonding of hypervalent main group compounds period 3 or higher such as the sulfate ion but in reality they are only ...
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Overlap matrix for finite sized square lattice of hydrogen atoms

So I'm trying to use the LCAO method to calculate molecular orbitals on a square lattice of hydrogen atoms. To this end, I need to compute the Hamiltonian matrix. With the nearest neighbor interaction ...
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1answer
56 views

Why must there be degeneracy in the orbitals to have a Jahn-Teller effect? [closed]

Why is it the case that for Jahn-Teller effects to occur in transition metals there must be degeneracy in either the $\mathrm{t_{2g}}$ or $\mathrm{e_g}$ orbitals?
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Sigma bond by combining two p orbitals

If I combine two p orbitals in such a way that they form σ bonds, which linear combination will represent bonding and antibonding? My work on this problem: $$ \begin{align} &\text{Bonding:} &...
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Energy level of molecular orbitals in heteronuclear diatomic compounds

I have been studying the molecular orbital theorem. I read that the energy levels for the $\ce{p}$ orbitals in the first series of $\ce{p}$ block molecules are something to the tune of $$\pi_x=\pi_y&...
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1answer
154 views

Energies of Virtual Molecular Orbitals (LUMO)

I just had a question about molecular orbitals. I was just wondering if the energies of the LUMO (virtual orbitals) derived from CCSD(T)/cc-pTVZ calculations could be trusted. I remember reading some ...
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1answer
68 views

Is there a hypervalent molecule which has no contribution of d-orbitals at all?

I thought that d-orbitals were used to "extend the octet rule" in these molecules until I looked it up on Google and saw that they actually contributed only a little to the molecule. A little, but not ...
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57 views

Relative Energies between LGOs and 2s orbital of oxygen in H2O MO Diagram

In this MO diagram, we find that the LGOs of the two premixed H1s orbitals are significantly higher in energy than oxygen's 2s orbital. Although oxygen's $Z_{eff}$ is considerably higher, is it really ...
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On mathematics behind molecular orbital energies

When explaining the mathematics behind calculating molecular orbital energy , namely HOMO and LUMO energies, using quantum chemistry, Chainer Chemistry documentation states that From mathematical ...
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Mathematical relation between bond angle and fraction of s or p character

In Concise Inorganic Chemistry by J.D.Lee (Adapted by Sudarsan Guha, Fourth Edition), on page 75, under the topic "Effect of Electronegativity - When the surrounding atom is same with different ...
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Stabilizing donor-acceptor interaction between orthogonal orbitals in the SN2 transition state?

For the $\mathrm{S_N2}$ reaction between chloroacetone and iodide, my professor has drawn a donor-acceptor interaction between the iodine lone pair attacking the Cl-substituted carbon and the π ...
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diborane fragment orbitals energy of dihydrogen

I want to ask a question about the fragment orbitals of the $\ce{B2H6}$ system, specifically when I combine the $\ce{B2H4}$ with the $\ce{H2}$ fragments. I am halfway through my inorganic chemistry ...
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Varying sizes in LUMO of acrolein

I want to ask a question about the varying sizes in the LUMO of acrolein during a 1,2- or 1,4-addition. Today in our introductory lesson to Organic Synthesis with 1,2- and 1,4-addition we were ...
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How to deal with non-symmorphic space groups for orbital/vibrational analysis?

I am learning about how to apply group theory analysis of MO diagrams and vibrational in the solid state context (not isolated molecules). I think the strategy for calculating representations and ...
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117 views

Sulfur can violate the octet rule because it has an “empty D orbital” is there any other information the periodic table isnt telling us?

In sulfur or any atom with an expanded octet on the 3rd row, where does the idea that they have an empty D orbital come from ?
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Calculating the Molecular Orbitals of a Molecular State [closed]

I am performing ab initio calculations on a heteronuclear diatomic compound using the MRCI method on the MOLPRO quantum chemistry package. I obtained the molecular states of the compound but I was ...
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187 views

What is the purpose of phase matching when drawing a MO diagram?

During the lecture, we were learning how to draw the MO diagram for $\mathrm{BF_3}$. I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My ...
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Properties that probe electron kinetic energy

This post is inspired by a question regarding the meaning of off-diagonal elements of the KE matrix (in some AO basis). One answer suggests that a diagonalized KE matrix might not be very useful. I ...
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221 views

Molecular orbital energies prediction with ML algorithms

In the recent years, computational chemistry community has focused on Machine Learning algorithms to predict molecular properties. Unfortunately, many of the authors of such papers are not chemists, ...
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Based on Molecular Orbital Theory , how is it decided that the double bond in O2 molecule has one sigma bond and one pi bond?

My Chemistry textbook says this in regard to a C2 molecule: It is important to note that double bond in C2 consists of both pi bonds because of the presence of four electrons in two pi ...
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Is Octet Expansion appropriate when regular Octet bonding is possible (such as using dative bonds)?

I was taught to use Occam's razor whenever in doubt over an octet expansion, being told it never happened when, for example, dative bonds could resolve the issue with a regular octet. This seems to ...
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Two questions about MO diagrams [duplicate]

In $\ce{HF},$ the $\mathrm{1s}$ orbital of $\ce{H}$ matches the $\mathrm{2p}$ orbital of $\ce{F}.$ However, in $\ce{LiF},$ the $\mathrm{2s}$ orbital matches the $\mathrm{2p}$ orbital. I knew that the ...
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Finding out more stable conformer via molecular orbital interaction

Out of these two, which one is more stable? I'm unable to imagine the orientation of the lone pairs of O and ABMO of C and Cl bond. Any tips to tackle these kind of problems?
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Explanation of SN2 Mechanism using MOT

SN2 is usually explained by MOT, where we state that the incoming nucleophile starts donating the electron density into the σ∗ orbital and the carbon-leaving group bond weakens and finally breaks and ...
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Why are sulfur trioxide and nitrate not isoelectronic, even though both have the same number of outer electrons?

Though $\ce{SO3}$ has the same number of outer electrons as $\ce{NO3-}$, the two are not isoelectronic. This statement is from JD Lee, but I could not understand why is he calling these two molecules ...
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477 views

Why CO is a stronger and more common ligand than N2?

Both N2 and CO are considered sigma-donor and pi-acceptor. Their MO diagram is similar, so I wonder why CO binds generally more strongly and it is a more common ligand.
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Cycloaddition vs Electrocyclic Pathway [closed]

Is there a molecular orbital/Woodward-Hoffmann explanation as to why Diels-Alder reactants don't commonly undergo electrocyclization instead of cycloaddition?
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Molecular Orbitals (only pi system) of Allyl system using group theory

I have just started reading group theory and their applications in the MO theory. I tried to get the equations of the pi molecular orbitals of allyl system using group theory, but I am stuck at the ...
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1answer
279 views

Antibonding, Nonbonding and Bonding orbitals

Recently I came across nonbonding orbitals. I know something about bonding and antibonding orbitals and their formation, but I have no idea about nonbonding orbitals. Could someone explain their ...
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Why is triatomic hydrogen relatively short-lasting?

The first chapter of Fleming's "Molecular Orbitals and Organic Interactions," describes the formation of triatomic hydrogen. In summary, the sigma MO of diatomic hydrogen interacts in phase with the ...
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142 views

Crystal field splitting energy of hexaaqua copper(II) and hexaaqua iron(II)

I am performing an experiment for the IB diploma program to determine the crystal field splitting energy of d-orbitals of different transition metal ions when they are complexed with ligands. In my ...
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How can I obtain the wave function of the dihydrogen system, by hand using Self Consistent Field DFT calculations? [duplicate]

After doing some energy calculations for the $\ce{H2}$ system in Gaussian, using ωB97X-D/STO-3G level of theory, and generating a .wfn file, I wanted to understand better how the computer does ...
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87 views

Adding cyanide vs nitrite for nucleophilic substitution and why does it change when we use silver salts for it

On adding $\ce{NaCN}$ to $\ce{RX}$, we get $$\ce{NaCN + RX -> RCN + NaX}$$ And not $\ce{RNC}$. Clayden gives the explanation as follows: Although linear cyanide (which is isoelectronic with $\...
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Gauche conformations for 14-electron AH2BH2 systems

The hydrazine molecule, and the similar sulfonium/Oxonium ylides, all have a gauche conformation that is more stable than the anti conformation. Is there any particular reason for this pattern? ...