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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2answers
610 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
275 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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How do molecular properties emerge from elemental ones? [closed]

Water, as we know, is not the sum of the properties of elemental hydrogen and oxygen, both of which are gases at room temperature. This is true of innumerable molecules and compounds. In general, ...
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Substitution reaction with pentacoordinate silicon intermediate [duplicate]

Why does electonegative atom, in our case fluorine, prefer to attack d orbital than antibonding σ orbital?What geometric constraints are they talking about? I need an answer in terms of d orbitals of ...
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29 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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34 views

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
30 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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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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60 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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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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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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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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45 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
44 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
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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
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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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34 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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2answers
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Confusion regarding orbital, electron and Quantum no’s

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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35 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
84 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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2answers
70 views

Why electrons do not distribute evenly among the atoms in a molecule? [closed]

I was wondering why the state where electrons are evenly (or the closest to being evenly) distributed among the atoms in a molecule is not the lowest energy state? For example, in a water molecule it ...
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38 views

Rigorous but terse introduction to molecular orbital theory

Is there a terse but rigorous introduction to MOT? I'm looking for the 'Berge's Real Analysis' of MOT, if that analogy resonates with anyone. If not, I'm looking for a book that I can use as a ...
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1answer
167 views

Why is oxygen more stable than oxygen dication?

According to molecular orbital theory (MOT), $\ce{O2^2+}$ has a greater bond order than $\ce{O2}$ and two less antibonding electrons. So why is molecular oxygen $\ce{O2}$ more stable than the ...
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Angle made by orbital with y-axis

What is the hybridization and angle (in degrees) with respect to the y-axis for the following hybrid orbital $ψ=\frac{1}{√3}c×(s-\frac{1}{√3}×p_x+\frac{√3}{√2}×p_y)$ The answer given is 30 degrees but ...
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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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2answers
133 views

Explanation of the orbital energies resulting from Jahn-Teller distortion of octahedral complex using MO theory

I am confused about the energies of the orbitals after Jahn-Teller distortion of an octahedral complex. Take elongation for example. To my understanding, since the ligands on the $z$ axis move away, ...
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1answer
159 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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1answer
53 views

Regarding the probability density of finding an electron in between a bond

I'd found the image attached on a website explaining the molecular orbital theory. My question is, shouldn't the graph have a maximum at the middle of the two hydrogen atoms? since my intuition tells ...
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32 views

are the exact and kohn-sham electron densities totally symmetric?

For any molecule with open or closed shells considering the electronic state to be the ground state: Is the exact electron density totally symmetric? is the Kohn-Sham electron density totally ...
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1answer
168 views

How can I know which molecule is more stable when bond order it's equal?

So, I was wondering, I have these molecules $\ce{O^+2}$, $\ce{O^-2}$, $\ce{O2}$ and $\ce{C^+2}$. When I try to find their bond order and their magnetic nature I get this: $\ce{O^+2} = \frac{1}{2} \...
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Can cycloaddition reactions be antarafacial?

Cycloaddition reactions of the form [4+2] and [2+2] are always suprafacial, as the geometry is too constrained to allow for antarafacial interaction between the FMO's. However, for cycloaddition of ...
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0answers
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How do bonds rotate in pericyclic reactions?

In Pericyclic reactions, it is shown that the terminal bonds rotate (conrotation or disrotation) to allow for allignment of the FMO's, thereby forming the sigma bond However, a detail that most of my ...
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2answers
103 views

Half sigma bonds

$\ce{N2+}$ has $2$ $\pi$-bonds and a half sigma bond. First of all, how can a "half" sigma bond exist? Usually when we encounter non integral bond orders, it is mostly because of resonance ...
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1answer
74 views

Origin of Virtual Molecular Orbitals in Hartree-Fock equations

Let's look at scheme Do I understand correctly, the origin of Virtual Orbitals is a solution of (for, exampre, restricted) HF equation eigenfuncions?
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1answer
81 views

Does cyclooctatetraene also have a diradical anti-aromatic electronic state?

I read that the molecular orbital diagram of cyclobutadiene predicts that it should have a diradical nature as it has two unpaired electrons in two degenerate non bonding orbitals (one in each). Why ...
6
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1answer
309 views

Why are hydrogen bonds in an antiparallel beta sheet stronger than those in parallel beta sheets?

Beta sheets are illustrated as such in most diagrams, where: In an antiparallel β-sheet, the polypeptide strands are arranged such that a $\ce{C=O}$ and an $\ce{NH}$ from adjacent strands face each ...
6
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1answer
140 views

Can we observe the shapes of MOs? [duplicate]

Condensed question formulation: Is there an experimental method to directly visualise the 3D form of a MO wave function, or at least the electron density associated with it? Full statement: ...
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1answer
67 views

Energy levels of combined orbitals

I saw the MO diagram for a NH3 molecule but couldn't understand why the combined atomic orbitals were in the positions they were, and if these positions were fixed. Why is the sigma anti bonding ...
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0answers
72 views

Help determining normalisation constant in SALC of methane

We have been told that a symmetry adapted combination of four hydrogen orbitals is used to create localised hydrogen orbitals for methane. These orthonormal combinations are denoted ψa1, ψt’2, ψt’’2 ...
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22 views

Question on symmetry-adapted, possibly antibonding combinations of core orbitals

In this question, it is said that the core electrons do mix and form delocalised, symmetry-adapted orbitals. The boron trifluoride molecule is often said to have no anti-bonding orbitals filled, with ...
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67 views

How to read character table?

I am having some problems reading character table. I will describe what I understand and thought to be right. Consider the $\pi$ MOs formed from overlap of p-orbitals in benzene. These two degenerate $...
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59 views

Molecular Orbital Theory and s-p mixing

I understand the bulk of MO theory , the formation of the bonding and anti bonding MOs etc. However, the topic about s-p mixing is quite puzzling to me. As a general rule of the thumb, I was taught ...
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1answer
54 views

Bonding in d10 metals such as Zn

I recently learned about the MO bonding model in metals, where many metal atoms form lots of orbitals close in energy that form bands. However, I can't understand the bonding in d10 metals. It seems ...
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1answer
55 views

Forcing atoms closer together [closed]

Is there a method in chemistry to alter the energy of atomic bonds by forcing atoms closer together in a smaller volume? Similar to how pressure squeezes atoms closer together.
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Molecular orbital diagram for carbene-metal and carbodiphosphorane-metal interaction

I am interested in understanding how carbenes and carbodiphosphoranes interact differently with a transition metals. I would like to use qualitative molecular orbital theory arguments (with an ...
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2answers
68 views

MO diagram when three orbitals of the same symmetry is allowed to mix

How exactly should we combine three orbitals when we have three orbitals that are of correct symmetry to interact? Take $\ce{H2O}$ for example. $\mathrm{2s},$ $\mathrm{2p}_z$ and the $A_1$ group $(\ce{...
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2answers
85 views

Insight into covalent bonds from electrostatic perspective

I try to understand, from the electromagnetic side only, how the molecule could be more stable than each atom, and concluded that it could not. Where is my mistake? Here is an illustration : By using ...
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0answers
51 views

Symmetry Operation on Product of Functions

In regards to direct product representations, I'm trying to find a proof for: $R(X_iY_j)=R(X_i)R(Y_j)$ Where $R$ is a symmetry operation of a group and $X_i$ and $Y_j$ are members of different basis ...
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250 views

Comparison between Molecular Orbital Theory and Valence Bond Theory

I have been reading about introductory Molecular Orbital Theory lately. Till now, I have used Valence Bond Theory to evaluate bonding. I have a few questions about it:- In VBT, we used the idea that ...

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