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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1answer
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Is strength of pi bonds greater than sigma bond of nitrogen molecule?

I am referring to MOT. In the nitrogen molecule(and elements of lower atomic number), sp mixing occurs and the sigma orbital set is raised above the pi orbital set. Shouldn't that mean that pi bond is ...
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3answers
719 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
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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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0answers
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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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0answers
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Rigorous but terse introduction to molecular orbital theory

Is there a terse but rigorous introduction to molecular orbital theory (MOT)? I'm looking for the 'Rudin's Real Analysis' of MOT, if that analogy resonates with anyone. If not, I'm looking for a book ...
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1answer
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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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1answer
39 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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1answer
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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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0answers
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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_\...
13
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2answers
299 views

Strange “far out” orbitals in HF and DFT calculations. Why do they occur?

I calculated some orbitals and I get quite strange results with orbital geometries I wouldn't expect from MO theory. A more experienced colleague just said: "That's always the case with big basis sets,...
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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
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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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How can antibonding orbitals be more antibonding than bonding orbitals are bonding?

In molecular orbital theory, the fact that a bonding and antibonding molecular orbital pair have different energies is accompanied by the fact that the energy by which the bonding is lowered is less ...
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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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1answer
257 views

Nature of a1g Molecular Orbital Interactions in Ferrocene

While learning about ferrocene I've come across this molecular orbital diagram. What particularly confused me is the nature of the a'1g orbital. My professor taught that a'1g and e2g are considered ...
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1answer
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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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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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1answer
310 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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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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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
388 views

What are the molecular orbitals of the hypothetical linear H₃⁺ molecule?

What would be the wave function of the lowest energy molecular orbital of a hypothetical linear $\ce{H3+}$ molecule? According to the LCAO method, I feel the lowest energy MO will be $\mathrm{1s(A) + ...
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1answer
488 views

What's the reaction type of the Hydrogen shift?

Rearrangement of cycloheptatrienyl carbene yields heptafulvene via a hydrogen shift. I see that the reaction is favorable because there is a conjugative effect with the $\pi$ system of the ring in ...
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1answer
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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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1answer
8k views

Delocalization of π-electrons in nitrate ion

Benzene and nitrate ion are given in my textbook as examples for the delocalization of π-electrons. Benzene, due to symmetry of its resonating structures, is simple enough. We assume that σ-electrons ...
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1answer
142 views

How should I construct the orbitals of dilithium using only pen and paper?

For a week I have lessons about quantum chemistry and I have a trouble understanding how to arrive at the good answer for the drawing of the orbital $(\ce{III})$ for $\ce{Li2}$ (see the second picture)...
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1answer
696 views

Why is carbon dioxide bent in its first excited state?

R. H. Crabtree writes in The Organometallic Chemistry of the Transition Metals (p 145, 6th ed.) that $\ce{CO2}$ is linear in the free state but bent [...] in the first excited state... Why is this ...
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1answer
3k views

What is the point of introducing virtual orbitals in Hartree-Fock calculations?

Let us for simplicity discuss RHF formalism. For $2n$-electron system we have $n$ Hartree-Fock equations written for $n$ spatial orbitals $\{ \phi_{k} \}_{k=1}^{n}$ $$ \newcommand{\mat}[1]{\boldsymbol{...
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1answer
257 views

Why does the binding of DMSO to metal via the S atom (k-S) strengthen the S=O bond?

So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\ce{\kappa-O}$ and $\ce{\kappa-S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given is that ...
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0answers
2k 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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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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2answers
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Symmetry representations for acetonitrile (CH3CN)

Can anybody share the symmetry labels for acetonitrile ($\ce{CH3CN}$), please? I mean to assign the symmetry labels to orbitals of acetonitrile
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1answer
165 views

Intuitive Explanation for why more negative charge on ligand does not imply more splitting effect?

I have studied coordination chemistry as part of my school curriculum and we covered Crystal Field Theory as our final theory, and the book says that Ligand Field Theory and Molecular Orbital Theory ...
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0answers
43 views

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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1answer
152 views

Carbon/silicon pentacovalent intermediate during substitution

During SN2 reaction with a silicon compound, a pentacovalent intermediate is formed, while there is no such intermediate formed with carbon compounds (only a pentacovalent transition state). Why is it ...
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31 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
31 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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0answers
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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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0answers
68 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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2answers
223 views

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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2answers
74 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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75 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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0answers
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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1answer
176 views

Frontier orbital analysis of zinc-catalysed carbonyl-ene reaction

Q1. Is the $\sigma_\ce{C-H}$ bond a donor in this reaction? If not, then can we take the alternate combination (HOMO of alkene, LUMO of the $\ce{C-H}$ bond and, HOMO of the carbonyl)? Q2. We can also ...
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35 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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0answers
62 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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0answers
48 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
62 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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0answers
40 views

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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