A method of studying bonds between atoms in which electrons' motions are defined as being all around the molecule, though influenced by nuclei.

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373 views

Do core electrons have molecular orbitals?

Valence electrons are associated with molecular orbitals and hybridizations. Do core electrons have molecular/hybridized orbitals, or the original atomic orbitals?
3
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1answer
151 views

Higher energy π HOMO

Which is higher in energy? Cyclohexanone enol or cyclohex-2-en-1-ol? Okay from what I understand a higher pi HOMO is synonymous with more nucleophilic. So I would expect cyclohex-2-en-1-ol to have ...
2
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1answer
44 views

Which is More Stable with Boranes: Amines or Phosphines?

Given borane's ($\ce{BH3}$) LUMO, which of these Lewis bases would have a more stabilizing interaction? In acid bases that means the higher HOMO and lower LUMO equals a stronger dative bond I ...
2
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1answer
38 views

HOMO and LUMOs of Carbon based Compounds

Why are the HOMO and LUMOs often $\pi$ orbitals in carbon based compounds that contain multiple double bonds or conjugation such as ethene and butadiene?
4
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2answers
231 views

Is s-p mixing referring to hybridization or is it the mixing of one atoms s orbital with the other's p orbital?

According to molecular orbital theory s and p orbitals can mix if they are close enough in energy to each other. For period 2 diatomics, this occurs for $\ce{Li, ~Be, ~B,~ C}$ and $\ce{N}$ - in the ...
4
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1answer
82 views

In molecular orbital theory, why does s-p mixing in the dinitrogen molecule not effect the 1σᵤ orbital?

s-p mixing in $\ce{N2}$ causes the $1\sigma _g$ orbital to decrease in energy, the $2 \sigma _g$ orbital to increase in energy (to higher than the $1 \pi _u$) yet the $1 \sigma _u$ is left unchanged ...
8
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4answers
189 views

Diels-Alder without molecular orbital theory

So the prof got to Diels-Alder without discussing it in the context of molecular orbital theory. Instead we got a resonance picture of what happens... this is what he told us: 1) 1,3-butadiene has ...
1
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1answer
35 views

MO scheme for coordination complexes (tetrahedral) - Heteroligand vs. homoligand

How is the MO diagram drawn for a tetrahedral complex with heteroligands (e.g. $\ce{[NiCl2(PPh3)2]}$) different from a tetrahedral complex with the same type of ligand? Do we consider the same "a1 and ...
3
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2answers
92 views

MO diagram of N2(2-)

In the MO diagram of $N_2^{2-}$, does s-p mixing happen (is the $п_{2p}$ orbital below or above sigma 2p)? As it is isoelectronic with oxygen, I think that the s-p mixing shouldn't happen.
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1answer
41 views

Which of the following molecules is more stable? [closed]

I want to know which molecule is more stable: $\ce{N2-}$ or $\ce{N2^2-}$. Also which has the greatest bond length?
3
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3answers
75 views

Why does symmetry have to be maintained in molecular orbitals?

Using the example of $\ce{XeF4}$: What is the physical explanation enforcing the symmetry of the $\ce{1b_{1g}}$ orbital on the fluorine atoms? Why isn't the symmetry of a nonbonding orbital ...
4
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1answer
149 views

why do 2 atomic orbitals form 2 molecular orbitals?

According to molecular orbital theory, two atomic orbitals form two molecular orbitals analogous to waves combining constructively or destructively but how can a wave combine destructively and ...
6
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2answers
263 views

How to know whether s-p mixing will happen in heteronuclear molecules?

How do I know whether s-p mixing would occur in some diatomic heteronuclear molecules like CN, CO, NO etc?
5
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2answers
693 views

Using MO theory, give an explanation for the C-C bond length in cyanogen

1. The problem statement, all variables and given/known data 2. The attempt at a solution I know that the MO diagram for CN- is this: I am unsure how to draw the MO diagram for cyanogen. I know ...
2
votes
1answer
823 views

Draw a simplified MO diagram for the pi system of Methyl vinyl ether

My attempt at the answers: i) 2 bond pairs and 2 lone pairs on oxygen atom therefore bond angle of slightly less than 109.5 degrees, around 104 degrees. ii) 120 degrees bond angle therefore sp2 ...
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2answers
377 views

How many electrons are there in the pi-system of cyanogen?

I know that there are 18 electrons available for bonding in the entire molecule, and that 6 of these are used for sigma bonds. That leaves 12 left over. Which molecular orbitals best describe the ...
2
votes
1answer
65 views

What is the usage of orbitals more complex than f orbitals?

Every high school learner, in each corner of the world, faces the lesson History of Atom during his courses, just as I did. We learned about s,p,d and f orbitals, though there were no signs of ...
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1answer
40 views

Search materials by HOMO, LUMO and work function

I need to search organic semiconductors for organic photovoltaics (OPV) by their HOMO, LUMO, work function at 300K (as I understand, WF cannot be derived from HOMO and LUMO because semiconductor can ...
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1answer
48 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 H3+ molecule? According to the LCAO method, I feel the lowest energy MO will be 1s(A) + 1s(B) + 1s(C). ...
1
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1answer
123 views

Delocalization of pi electrons in nitrate ion

In my textbook, as examples of delocalization of pi electrons, benzene and nitrate ion have been considered. Benzene, due to symmetry of its resonating structures is simple enough. We assume that ...
2
votes
1answer
148 views

How to explain the effect of hyperconjugation on the stability of alkenes with MO theory?

Hyperconjugation stabilizes carbocations and that makes sense because electrons are given to the empty p orbital. But how does it stabilize alkenes ? Can MOT be used to explain it ?
3
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1answer
29 views

Non stationary effects of molecular orbitals

We have been learning a bit about molecular orbitals in class. However, we have always considered things under a quasistatic approximation. What are some effects that can only be explained by not ...
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1answer
47 views

How is ethanenitrile protonated?

I know that the proton will attack the HOMO, but I'm having difficulty imagining how this will happen. Thank you.
3
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1answer
202 views

How can BN be paramagnetic?

I read something recently that said "BN has been observed in the gas phase, is paramagnetic, and has a vibrational frequency lower than N2. These properties can be explained by the molecular orbital ...
2
votes
1answer
610 views

Why does AlCl3 dimerise to Al2Cl6 at low temperatures?

I know that it has something to do with HOMOs and LUMOs (I can't what the HOMO/LUMO for AlCl3 is, though).
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0answers
41 views

Relating Molecular Orbital Theory and Valence Bond Theory

As I have studied both the theories only superficially, I am unable to correlate them. I would like to know the link between the two.
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1answer
72 views

Molecular Orbital Theory and No. of bonds

The order of filling of molecular orbitals $\ce{O2}$ by MOT is this : But from it, how can I deduce that there is one sigma and one pi bond in an oxygen molecule ?
2
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1answer
206 views

The “rules” for LCAOs in Molecular Orbital Theory

In our course on physical chemistry, which involves MOT, we have been taught that in the LCAO approach, the wave function for a molecule... say hydrogen ion, can be approximated by a linear ...
2
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2answers
95 views

Why is an excited helium dimer created in this collision experiment?

Why does a collision between an excited helium molecule (He*) and a ground-state helium atom create He2*? Is it something to do with the lower-energy orbitals? I'm not really sure at all.
2
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1answer
41 views

MO theory methods other than LCAO

What methods other than linear combination of atomic orbitals does MO theory use? Which one is the most accurate and comprehensive?
3
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1answer
158 views

Why hybridization occurs in diatomic molecule

In diatomic nitrogen There are two electron configurations I'd like to compare: 1s2 2s2(lone pair) 2p3(the bonding electrons sigma,pi,pi) 1s2 2sp(lone pair) 2sp(sigma bonding) 2p2(pi,pi bonding) ...
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1answer
125 views

C=O and C=C antibonding orbitals

Why is the pi star orbital of the C=C bond higher in energy than the antibonding pi orbital of the C=O bond? I thought it was the other way around; it's relatively easy to add something to a C=C ...
3
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0answers
50 views

Irreducible Representations to Classify Atomic Orbitals [duplicate]

I have some major confusion on Irreducible Representations. An example of a problem i have is Based on the character table for the point group of each of the follwing molecules, which irreducible ...
5
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1answer
2k views

What are t2g and eg in CFT?

In the Crystal Field Theory, when the splitting of the d-orbital occurs, it gets divided into two parts... The upper part with higher Energy is the $t_{2g}$ and the lower part with lower Energy is ...
5
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1answer
201 views

Diatomic halogens - bond strength

Why is the F-F bond relatively weak? And why does bond strength decrease from Cl-Cl to I-I? Does this have anything to do with "lone-pair" repulsions on the rather small F-F molecule? I haven't ...
3
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2answers
63 views

Structure of benzene

How does molecular orbital or valence bond theory explain the delocalised structure of benzene? I.e. when the carbon forms 3 bonds with other carbons/hydrogen, what happens to the remaining hybridised ...
0
votes
1answer
327 views

How do you determine how many electrons occupy the anti bonding orbitals?

For molecular orbital theory: How do you determine how many electrons occupy the anti bonding orbitals? Also, why does hydrogen gas have no anti bonding orbitals- if each atom's electrons form a ...
4
votes
1answer
113 views

Asymmetry in trigonal bipyramidal geometry

I teach an MCAT course in chemistry. I like to explain VSEPR by saying.. first, imagine arranging electron pairs around the central atom so they are maximally distant from each other, and uniformly ...
5
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1answer
186 views

Show the vibrational frequency of F2- is much lower than that of F2

Basically I need to draw the molecular orbital for $\ce{F2}$ and then answer a bunch of questions about it. I have drawn it correctly, as far as I know, but I don't know how to use it to show that the ...
6
votes
2answers
477 views

How does a Frost diagram reproduce the solutions to the wave equation?

I came across a Frost diagram for cyclic compounds in my book, and all my book had to offer was that it geometrically reproduces the solutions of the wave equation, and can therefore determine the ...
2
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1answer
47 views

Quick way to find magnetic nature of compounds or ions

According to the Molecular Orbital Theory, the method to check whether a given compound is paramagnetic or diamagnetic is to draw the molecular orbitals and then to see whether we have all the ...
3
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1answer
106 views

Unequal ionization energies of methane

Why does methane have two different ionization potentials? How does this work? I understand that MO theory predicts C-H bonds of differing strength, while hybridization predicts C-H bonds of varying ...
5
votes
1answer
229 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 $\{ \phi_{k} \}_{k=1}^{n}$ $$ ...
2
votes
1answer
293 views

Which one, Mulliken charge distribution and NBO, is more reliable?

Sometimes the Mulliken and NBO turn out to be so different that I can't decide which one I can trust. I've heard that Mulliken is inaccurate, but is NBO always accurate? And should I use Gaussian or ...
0
votes
1answer
242 views

Nitric Oxide Dimerization

This is the molecular orbital diagram for nitric oxide: Now, we know that nitric oxide can dimerize. However, why does nitric oxide dimerize as to form an $\ce{N-N}$ bond? Why not an $\ce{O-O}$ ...
2
votes
1answer
392 views

Position of nodal planes in molecular orbitals

From the attached picture (MO diagram of cyclopentadienyl anion) I can figure out where the nodal planes are, but why are they exactly at these positions? Why is this nodal plane invalid?
3
votes
1answer
485 views

Energetic Placement of Atomic Orbitals in the HCl Molecular Orbital Diagram

How are the 3p orbitals of chlorine lower in energy than the 1s orbital of hydrogen?
3
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2answers
1k views

Why are least electronegative elements usually in center of lewis structure

Many sources state that one of the primary rules for molecular structures is that the least electronegative element is in the center. However, none of them explain why this is the case. Is this ...
5
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1answer
112 views

Electronic model with highest prediction rate

Among many models, including the valence bond model (VB) or the molecular orbital (MO) model, which are the ones with best predictive power? (e.g. the MO is thought to predict spectroscopic ...
6
votes
3answers
372 views

Do filled Orbitals also hybridize?

Recently I was watching a video on Valence Bond Theory, on the MIT Open-Course youtube channel. The teacher there said that for hybridization to occur, electron promotion from fully filled orbitals to ...