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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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Can anyone explain the structure of H2XeO4?

Using the obselete VSEPR theory I had a hard time predicting the structure of H2XeO4. So I looked it up. This was what I found. Its kind of wierd to me. I can't see how it happened. Can anyone explain ...
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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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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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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 ...
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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
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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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269 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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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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Can pi backdonation occur on non-metal centers?

The common example of backdonation 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 a ...
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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
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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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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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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
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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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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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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
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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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120 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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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
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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
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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
244 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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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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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
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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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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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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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267 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
90 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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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
123 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
70 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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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}...
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C5v E1 SALC production using Full Projection

I have another SALC question. @Andrew and @user5713492 did a phenomenal job clarifying my previous confusion with Methane T2 SALC production, so I attempted to apply this to a new point group, and ...
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1answer
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Molecular Orbital Mixing to get the Molecular Orbitals of a large molecule

I am trying to get the molecular orbital for arbitrarily placed nuclear centres (identical). In other words , I am trying to solve the following one electron hamiltonian. $$h=-\dfrac{1}{2}\nabla^{2}-\...
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Which atom bears the negative charge in cyanide? I am confused by the MO diagram

In heteronuclear species, whichever atomic orbital a molecular orbital is closer to in energy contributes more to that molecular orbital, right? In other words, if the orbital is occupied, more ...
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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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Methane T2 SALCs

So I have a question on the form of the $T_2$ SALCs of methane. Below I show the $T_d$ character table and the accompanying reducible representation for the sigma framework (using, in the case of ...
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MO Diagram “greatest stabilisation when orbitals are close in energy”

I was studying MO diagrams in Chemistry and we were given a diagram explaining this: I understood the diagram furthest to the left describing the situation where the Electrophile (E) and Nucleophile (...
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Why does NH3 hybridize at all?

So in Chemistry class I've been taught that hybridization is a way we can explain things such as how $\ce{CH4}$, for example, forms four, equally strong bonds. However at the same time I'm told that ...
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Why are pi antibonding orbitals lower in energy than sigma antibonding orbitals?

I know when a carbonyl group is attacked by a nucleophile, the electrons of the nucleophile enter the antibonding π orbital of the $\ce{C=O}$ bond, which breaks the π bond. My textbook says that ...
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Why is a carbon to iodine pi-bond less stable than a carbon to fluorine pi-bond?

This question comes from a second semester undergraduate organic chemistry course. Please refer to the image below with regard to the question. My understanding of the trend in section 4a is that "...
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1answer
146 views

ClO2 molecular orbital diagram?

I was trying to construct a MO diagram for ClO2, and since I'm not too sure about my final result I thought I'd check it from one of the experts here. ClO2 is of C2v point group, so I just read off ...
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Theory of symmetry breaking in water?

As we all know $\ce{H2O}$ is bent ($C_\mathrm{2v}$) in its ground state equilibrium structure, rather than linear ($D_\mathrm{\infty h}$), which can be readily understood e.g. from the MO diagram of ...
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Does a neutral dimercury molecule exist?

Is a neutral $\ce{Hg2}$ molecule possible, as a gas under extremely low (partial) pressures? What is the enthalpy of formation or similar? It is my impression that usual mercury vapors are monatomic? ...
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Explaining why s and p orbitals do not interact

While going through molecular orbital theory, my chemistry teacher mentioned that the reason why there is no significant interaction between $\ce {s}$ orbitals on one atom and $\ce {p_x}$ and $\ce {...
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Structure of (CH3COO)3Fe

I'm a grade 12 student trying to comprehend MOT & LFT in Co-ordination compounds. For one of our salt analysis(practicals), the test for acetate ion includes the addition of Neutral Ferric ...
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Guidelines on qualitatively drawing MOs

I would just like to clarify the guidelines of drawing MOs formed from interactions between AOs. Strangely, this topic is rarely touched on in most books on molecular orbital theory. The following are ...
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Consequence of interactions between filled orbitals

It is known that the interaction between filled orbitals from the perspective of molecular orbital theory is overall destabilising because antibonding MOs are more antibonding than bonding MOs are ...
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How do three-electron bonds work in MO theory?

When we're taught MO theory in basic chemistry, a rule-of-thumb hammered into our heads is that an orbital takes up to 2 electrons with opposite spins. Sigma or pi bonds are represented by stable ...