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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why must there be degeneracy in the orbitals to have Jahn Teller effect
Why is it the case that For Jahn-Teller effects to occur in transition metals there must be degeneracy in either the t2g or eg orbitals?
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Sigma bond by combining two p orbitals
If I combine two p orbitals in such a way that they form σ bonds, which linear combination will represent bonding and antibonding?
My work on this problem:
$$
\begin{align}
&\text{Bonding:} &...
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0answers
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Energy level of molecular orbitals in heteronuclear diatomic compounds
I have been studying the molecular orbital theorem. I read that the energy levels for the $\ce{p}$ orbitals in the first series of $\ce{p}$ block molecules are something to the tune of $$\pi_x=\pi_y&...
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1answer
144 views
Energies of Virtual Molecular Orbitals (LUMO)
I just had a question about molecular orbitals. I was just wondering if the energies of the LUMO (virtual orbitals) derived from CCSD(T)/cc-pTVZ calculations could be trusted. I remember reading some ...
2
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1answer
56 views
Is there a hypervalent molecule which has no contribution of d-orbitals at all?
I thought that d-orbitals were used to "extend the octet rule" in these molecules until I looked it up on Google and saw that they actually contributed only a little to the molecule. A little, but not ...
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1answer
34 views
Relative Energies between LGOs and 2s orbital of oxygen in H2O MO Diagram
In this MO diagram, we find that the LGOs of the two premixed H1s orbitals are significantly higher in energy than oxygen's 2s orbital. Although oxygen's $Z_{eff}$ is considerably higher, is it really ...
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1answer
75 views
On mathematics behind molecular orbital energies
When explaining the mathematics behind calculating molecular orbital energy , namely HOMO and LUMO energies, using quantum chemistry, Chainer Chemistry documentation states that
From mathematical ...
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25 views
Constructing a π-system given a molecular formula
Is there a simple way to construct a π-bond system (the molecular bond diagram but solely for π-bonds) for a polyatomic molecule solely being provided a molecular formula (i.e. benzene $\ce{C6H6})?$
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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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26 views
Stabilizing donor-acceptor interaction between orthogonal orbitals in the SN2 transition state?
For the $\mathrm{S_N2}$ reaction between chloroacetone and iodide, my professor has drawn a donor-acceptor interaction between the iodine lone pair attacking the Cl-substituted carbon and the π ...
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+100
diborane fragment orbitals energy of dihydrogen
I want to ask a question about the fragment orbitals of the $\ce{B2H6}$ system, specifically when I combine the $\ce{B2H4}$ with the $\ce{H2}$ fragments.
I am halfway through my inorganic chemistry ...
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Varying sizes in LUMO of acrolein
I want to ask a question about the varying sizes in the LUMO of acrolein during a 1,2- or 1,4-addition.
Today in our introductory lesson to Organic Synthesis with 1,2- and 1,4-addition we were ...
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0answers
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How to deal with non-symmorphic space groups for orbital/vibrational analysis?
I am learning about how to apply group theory analysis of MO diagrams and vibrational in the solid state context (not isolated molecules).
I think the strategy for calculating representations and ...
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1answer
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Sulfur can violate the octet rule because it has an “empty D orbital” is there any other information the periodic table isnt telling us?
In sulfur or any atom with an expanded octet on the 3rd row, where does the idea that they have an empty D orbital come from ?
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Calculating the Molecular Orbitals of a Molecular State [closed]
I am performing ab initio calculations on a heteronuclear diatomic compound using the MRCI method on the MOLPRO quantum chemistry package. I obtained the molecular states of the compound but I was ...
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117 views
What is the purpose of phase matching when drawing a MO diagram?
During the lecture, we were learning how to draw the MO diagram for $\mathrm{BF_3}$.
I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My ...
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0answers
26 views
Properties that probe electron kinetic energy
This post is inspired by a question regarding the meaning of off-diagonal elements of the KE matrix (in some AO basis). One answer suggests that a diagonalized KE matrix might not be very useful. I ...
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1answer
186 views
Molecular orbital energies prediction with ML algorithms
In the recent years, computational chemistry community has focused on Machine Learning algorithms to predict molecular properties. Unfortunately, many of the authors of such papers are not chemists, ...
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1answer
49 views
Based on Molecular Orbital Theory , how is it decided that the double bond in O2 molecule has one sigma bond and one pi bond?
My Chemistry textbook says this in regard to a C2 molecule:
It is important to note that double bond
in C2 consists of both pi bonds because of the
presence of four electrons in two pi ...
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0answers
29 views
Is Octet Expansion appropriate when regular Octet bonding is possible (such as using dative bonds)?
I was taught to use Occam's razor whenever in doubt over an octet expansion, being told it never happened when, for example, dative bonds could resolve the issue with a regular octet. This seems to ...
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30 views
Two questions about MO diagrams [duplicate]
In $\ce{HF},$ the $\mathrm{1s}$ orbital of $\ce{H}$ matches the $\mathrm{2p}$ orbital of $\ce{F}.$ However, in $\ce{LiF},$ the $\mathrm{2s}$ orbital matches the $\mathrm{2p}$ orbital. I knew that the ...
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Finding out more stable conformer via molecular orbital interaction
Out of these two, which one is more stable? I'm unable to imagine the orientation of the lone pairs of O and ABMO of C and Cl bond.
Any tips to tackle these kind of problems?
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Explanation of SN2 Mechanism using MOT
SN2 is usually explained by MOT, where we state that the incoming nucleophile starts donating the electron density into the σ∗ orbital and the carbon-leaving group bond weakens and finally breaks and ...
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0answers
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Why are sulfur trioxide and nitrate not isoelectronic, even though both have the same number of outer electrons?
Though $\ce{SO3}$ has the same number of outer electrons as $\ce{NO3-}$, the two are not isoelectronic.
This statement is from JD Lee, but I could not understand why is he calling these two molecules ...
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259 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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1answer
46 views
Cycloaddition vs Electrocyclic Pathway [closed]
Is there a molecular orbital/Woodward-Hoffmann explanation as to why Diels-Alder reactants don't commonly undergo electrocyclization instead of cycloaddition?
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1answer
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Molecular Orbitals (only pi system) of Allyl system using group theory
I have just started reading group theory and their applications in the MO theory. I tried to get the equations of the pi molecular orbitals of allyl system using group theory, but I am stuck at the ...
2
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1answer
108 views
Antibonding, Nonbonding and Bonding orbitals
Recently I came across nonbonding orbitals. I know something about bonding and antibonding orbitals and their formation, but I have no idea about nonbonding orbitals. Could someone explain their ...
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0answers
45 views
Why is triatomic hydrogen relatively short-lasting?
The first chapter of Fleming's "Molecular Orbitals and Organic Interactions," describes the formation of triatomic hydrogen. In summary, the sigma MO of diatomic hydrogen interacts in phase with the ...
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0answers
83 views
Crystal field splitting energy of hexaaqua copper(II) and hexaaqua iron(II)
I am performing an experiment for the IB diploma program to determine the crystal field splitting energy of d-orbitals of different transition metal ions when they are complexed with ligands.
In my ...
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34 views
How can I obtain the wave function of the dihydrogen system, by hand using Self Consistent Field DFT calculations? [duplicate]
After doing some energy calculations for the $\ce{H2}$ system in Gaussian, using ωB97X-D/STO-3G level of theory, and generating a .wfn file, I wanted to understand better how the computer does ...
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1answer
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Adding cyanide vs nitrite for nucleophilic substitution and why does it change when we use silver salts for it
On adding $\ce{NaCN}$ to $\ce{RX}$, we get
$$\ce{NaCN + RX -> RCN + NaX}$$
And not $\ce{RNC}$. Clayden gives the explanation as follows:
Although linear cyanide (which is isoelectronic with $\...
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Gauche conformations for 14-electron AH2BH2 systems
The hydrazine molecule, and the similar sulfonium/Oxonium ylides, all have a gauche conformation that is more stable than the anti conformation.
Is there any particular reason for this pattern? ...
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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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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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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
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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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32 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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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
212 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
74 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
50 views
Ab Initio and Molecular Orbitals [closed]
What is the difference between ab initio calculations and molecular orbital theory?
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1answer
60 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
158 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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52 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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2answers
119 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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1answer
70 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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188 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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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
49 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 ...
