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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45 views

Electronic States of the (unstable) tetrahedral CrCl4

I was probing for first order Jahn-Teller instability in the coordination complex CrCl4 (2 electrons in E set). Taking the direct product yields the states A1 + A2 + E, so I took the symmetric and ...
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91 views

Is any symmetry element conserved during a supra-antarafacial cyclo addition of two cis-butadiene units

I tried to construct a correlation diagram for the [4+4] cyclo addition of two cis-butadiene units. But I failed to construct any meaning full orbitals for the "educt" side where the two butadiene ...
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115 views

Is there a reliable chemical theory that predicts pKa based on structure?

Obviously, there are general stability arguments that can be made to estimate relative pKas, such as evaluating the stability of the conjugate base of an acid, or thinking about how polarized the bond ...
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1answer
103 views

Is fluorine also hybridised in carbon tetrafluoride?

I had read that when an atom forms multiple bonds, it hybridises it's orbitals to minimise the repulsion and decrease the overall energy. But do the terminal atoms also exist in hybridised form? E.g. ...
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35 views

Ionization energy and charge localization: π-bonds/systems and ionization energy

Page 35 of my textbook, Mass Spectrometry by Jürgen H. Gross, says the following in a section on ionization energy (IE) and charge localization: Molecules with π-bonds have lower IEs than those ...
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117 views

HOMO orbitals of B-N from an MO diagram

I want to ask a question about the MO diagram of BN. I was provided with the following question and answer and describe the situation occurring: After performing the s-p mixing for BN, I found this ...
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4answers
293 views

Why do solutions of electron in a box (and in a ring) predict coefficients for LCAO (linear combination of atomic orbitals) in 1D systems?

The solutions to the 1D particle in a box quantum mechanic system are standing waves (zero at both ends of the box) with 0,1,2... nodes for increasing energy (zero for the ground state). If I look ...
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1answer
139 views

Band MO of Sodium Filling of electrons confusion

I wanted to ask a question about metallic bond - band electron theory. Consider the diagram of Sodium below: Circled are orbitals both containing $2$ electrons each which combine using LCAO to give ...
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1answer
57 views

Ab Initio and Molecular Orbitals [closed]

What is the difference between ab initio calculations and molecular orbital theory?
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1answer
71 views

FMO analysis of the [3,3] Sigmatropic reaction regarding geometry. Is it accurate?

While studying the reasons behind the stereospecificity of [3,3] Sigmatropic reactions, I ran into an image portraying both possible transition states for the reaction: The Chair TS and Boat TS. The ...
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1answer
288 views

In the Lewis structure for barium fluoride, why does barium lose its valence electrons?

I searched for $\ce{BaF2}$ Lewis structure, and found out that the Barium atom loses its 2 valence electrons to form $\ce{F- Ba^2+F-}$. Before seeing it I thought each of $\ce{Ba}$'s valence ...
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57 views

Group theory and the orbitals of benzene

Can I apply group theory to the $\sigma$ orbitals of benzene? I have already seen it be applied to the $\pi$ orbitals, but I can't find an application to the $\sigma$ in literature. In this case, ...
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125 views

Is dihydrogen the only example of overlap between two s orbitals?

I heard that $\ce{H2}$ is the only example of s–s orbital overlap. Can anyone give an example which contradicts this statement?
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114 views

Molecular Orbital Hybridization vs Delocalization for positive charge stabilization

While studying Molecular Orbital Theory, I ran into a comparison of basicity between pyridine and piperidine. The latter was concluded to be more basic because of the sp3 hybridization of the ...
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259 views

Can 2 dz2 orbitals form a π bond?

Usually , d orbitals overlap sideways along a common internuclear axis, but drawing and checking for dz2 , it always seems to form a sigma bond or null overlap. Is this because it doesn't have any ...
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57 views

Determine HOMO and LUMO of compounds

I have the reaction below and am asked to determine the HOMO and LUMO of the two reactants. I know that the cyanide anion will be the nucleophile since it is donating an electron pair to the ...
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1answer
64 views

How does hyperconjugation explain stability of partial positive charges?

Recently I was reading this answer to the question Why does boron add to the less substituted carbon in the hydroboration of an alkene?. See the transition state given in the above answer, and the ...
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1answer
205 views

What is the explanation of the structure of H2XeO4?

Using the obsolete VSEPR theory I had a hard time predicting the structure of $\ce{H2XeO4}$. So I looked it up. I found the molecule via chemapps.stolaf.edu: It looks weird to me. I can't explain the ...
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1answer
609 views

Does peroxide ion have any unpaired electrons?

According to the MOT diagram there are no unpaired electrons but in an exam I gave the answer key said it has 2 unpaired electrons. I can also find some images on google where it has 2 unpaired ...
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1answer
395 views

Molecular orbitals of the enolate ion

The reactivity of the enolate ion is most frequent explained with reference to its system of $\pi$ molecular orbitals. The image below taken from Wikimedia Commons depicts this system of $\pi$ ...
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176 views

Why is the HOMO always lower in energy than the LUMO?

We say that increasing the energy of the $\ce {HOMO}$ of molecules increases their reactivity towards electrophiles while decreasing the energy of the $\ce {LUMO}$ increases their reactivity towards ...
12
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1answer
191 views

What is the physical origin of conjugation?

I had a question about the origins of conjugation in conjugated molecules. Take two ethylenes as compared to butadiene. Huckel seemed to argue that conjugation was the result of pi-pi stabilization ...
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1answer
225 views

Why does Methyl Carbocation have p orbital

For a carbocation to form, it needs to lose an electron. In the example below the leaving group is Br and the products are a methyl carbocation and a bromide ion. What I am unsure about is why the ...
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359 views

Why is a LCAO necessary within Hartree Fock?

As I understand it, the electronic Schrödinger equation cannot be solved for polyelectronic systems. To circumvent this problem in the Hartree-Fock method, it is assumed that the polyelectronic ...
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62 views

Protonation of pyridine

Recently, I have been reading the Nobel Lecture given by Kenichi Fukui when he won the Nobel Prize in 1981, for his contributions to the development of Frontier Molecular Orbital Theory. One of the ...
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109 views

Can pi backdonation occur on non-metal centers?

The common example of back-donation is the interaction of a CO molecule with a metal center (d-orbitals) on a surface. Can a similar mechanism occur between CO and a non-metal center, like oxygen on ...
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86 views

Variational method: Hydrogen atom ground state in STO-3G basis expansion

I computed numerically the ground state energy of hydrogen by variational procedure, firstly expanding the wave function over the s-wave basis set STO-3G $$\psi(r)=\sum_{i=0}^3 C_{i} e^{-\alpha_ir^2}$$...
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1answer
67 views

How does hyperconjugation in alkenes affect bond lengths?

I understand how the diagram below results in hyperconjugation stabilising alkenes. Essentially, the C-H sigma bonding orbital interacts with the pi bonding orbitals creating two molecular orbitals. ...
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1answer
625 views

Reasons for low melting point of gallium

J.D. Lee writes in Concise Inorganic Chemistry: Gallium has an unusual structure. Each atom has one closest neighbor at a distance of 2.43 Å. This remarkable structure tends towards discrete ...
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2answers
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MO diagram of BeH₂

I was learning about the MO diagrams of triatomic molecules and was left slightly confused about $\ce{BeH2}$. A picture of the MO is shown below: When looking at the $\mathrm{1s}$ combinations, I ...
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1answer
157 views

notation on MO diagrams

I wanted to ask a question about notations on MO diagrams. Our first lesson about MO diagrams was today and I was taken through an example with $\ce{F2}$ as shown below: but one thing that the ...
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164 views

Hartree Fock for an atom (Beryllium)?

I'm working on solution of Hartree-Fock equation for Beryllium in configuration $1s^2 2s^2$, expanding the orbital with STO-3G basis $$\phi_k=\sum_{p=0}^3 C_{kp}e^{-\alpha_{kp}r^2}$$ I know the values ...
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55 views

water molecule orbitals in MO=LCAO theory

In the picture below I have evaluated the combinations of atomic orbitals which belong to the same symmetry specie using the standard method with the character table. Now I think that in order to ...
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2answers
54 views

Predict the number and nature of bonds using Molecular Orbital Theory

I found the following question in a high school chemistry problem book: According to Molecular Orbital Theory which of the following is true: (A) In $C_2$ molecule both the bonds are $\pi$ ...
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2answers
310 views

Why is manganate ion paramagnetic [closed]

When I tried to figure out why manganate ion is paramagnetic, given that its oxidation number is +6, I am not able to understand why there are unpaired electrons. Is it the case that six of the seven ...
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70 views

Antiaromaticity can be explained by Hückel method?

Pentalene is one of the most famous antiaromatic molecules. But I obtained its energy of $\pi$ system as $8\alpha+10.46\beta$ by Hückel method (with a bit complicated but straightforward calculation). ...
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1answer
40 views

Struggling to understand wavevector K for deriving energy levels in reciprocal space [closed]

I don't really understand why, when deriving wavefunctions for arrays of atoms, the wavevector k is introduced and the general idea surrounding momentum space. please help!!
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1answer
122 views

Possible erratum in solutions to Orbital Interactions in Chemistry 2ed [closed]

I was attempting the problems in Chapter 1 of Orbital Interactions in Chemistry, and found a slight problem. ftp://ftp.wiley.com/public/sci_tech_med/orbital_interactions_2e/Chapter%201%20-%20Answers....
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1answer
264 views

Pauli exclusion principle

Pauli exclusion principle states that 'No two electron can exist in same state' or 'No two electron can have same set of quantum numbers'. But in reality there is no state of electron. The state is ...
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73 views

How do we get the wave function of Ligand Group Orbitals with the same symmetry as that of the corresponding metal orbitals

In the book Principles of Structure and Reactivity by Huheey, Chapter 14, the author has taken linear combination of ligand orbitals to form ligand group orbitals and then further combination of LGOs(...
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3answers
489 views

Linear Combination of Atomic Orbitals

In Atkins Physical Chemistry 10th edition in chapter number 10B it is given that within the Born-Oppenheimer approximation, the Schrödinger equation can be solved for the molecular species $\ce{H2+}$ ...
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1answer
61 views

Mixing of molecular orbitals in polyatomic molecules

I am trying to solve the following Hamiltonian,$$H=-\frac{1}{2}\nabla^{2}-\sum_{i=1}^{10}\frac{1}{|\vec{r}-\vec{R_{i}}|}$$ Here $Z=1$ . To get all ther molecular orbitals of this system. I took the ...
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25 views

Do species with more unpaired electrons attract magnets more strongly than those with fewer unpaired electrons?

My lecture notes state that you can distinguish between high spin and low spin complexes by their magnetic properties. This thought came to me: consider two octahedral crystal fields with a d7 ...
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57 views

What are the pi-MOs in anisole like?

The $\pi$-orbitals of benzene are well known and given in any standard undergraduate textbook. When considering anisole, phenol, etc, a lone pair in a p orbital of the O can delocalise into the $\pi$-...
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1answer
513 views

Valence bond theory and molecular orbital theory — how do they complement one another?

Based on my readings, valence bond theory (VBT) and molecular orbital theory (MOT) tend to complement one another in explaining a molecule, but I don’t understand how VBT helps us explain the ...
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1answer
191 views

Oxalate Anion MO Diagram

I figured I’d study $\ce{C2O4^2-}$ as an organometallic ligand, and found that it is weak field (pi donor). I hence decided to construct a MO diagram. The oxalate anion is of D2h symmetry, so one ...
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82 views

Hydrogen Bonding in Water (MO theory)

Valence Bond Theory tells us that each of the “sp3” (in reality, 44% s character) oxygen line pairs in water can act as electron donors, but observing the MO diagram for water tells us that the 2 non-...
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1answer
343 views

C4v point group complexes and the group orbitals (MO Theory)

Out of curiosity, what would the group orbitals be like in a C4v complex (square planar complexes or octahedral complexes with 5 identical ligands and 1 other) look like? I get a irreducible ...
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1answer
175 views

MO diagram for pentaamminechlorocobalt(III)?

I was considering the MO diagram for [Co(NH3)5Cl]2+, and figured it’d be as follows: 5 sigma interactions from the NH3 ligands; by reducing a reducible representation one obtains 2A1 + B1 + E 2 pi ...
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1answer
92 views

Quantitative MO theory- how is the overlap integral and the weighting coefficients of the molecular orbital actually evaluated?

Title. In my inorganic chemistry course, we learn about SALCs and qualitative MO treatment, with only a fleeting reference to the S integral and actual molecular wave functions (only hydrogen, $\ce{H2}...