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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20
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1answer
7k views

How can the intense color of potassium permanganate be explained with molecular orbital theory?

In the permanganate ion, manganese is in the $+7$ oxidation state, therefore it is a $\ce{d^0}$ ion. $\ce{d^0}$ and $\ce{d^1^0}$ ions don't absorb visible spectrum radiation because there are no ...
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2answers
2k views

Formation of Bonding and Anti-bonding Molecular Orbitals

If two orbitals combine in-phase, a bonding molecular orbital is formed. When they combine out-of-phase, an anti-bonding molecular orbital is formed. For a single molecule, how are both orbitals ...
5
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1answer
1k views

Why do closo-boranes have a 2− charge?

In a question I was solving, it was mentioned that: [...] closo-boranes are compounds having the general formula $\ce{B_nH_n^2-}$ [...] an example is $\ce{B6H6^2-}$. Why do these boranes possess a ...
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1answer
922 views

Physical Meaning of the Difference between MO and VB Wave Function of H2?

What would be the physical meaning of the difference between the MO wave function and VB wave function of $\ce{H2}$?
8
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2answers
476 views

Alternative Program for Orbital Population Analysis

Gaussian has Orbital-by-Orbital Population Analysis. From the manual: ...
12
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1answer
2k views

Destabilization of antibonding MO vs stabilization of bonding MO

My textbook writes that The net energy stabilization due to the occupation of a bonding MO is equal to the net energy destabilization due to the occupation of the corresponding antibonding MO. ...
-2
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1answer
147 views

Creating Pi Molecular Orbitals from P Atomic Orbitals

As shown in the image, we have two free p orbitals in ethene but we need two p orbitals each for the bonding and anti-bonding orbital. That is a total of four. What is the concept behind this?
6
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1answer
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Hybridization, MOT and Paramagnetism

In what way can hybridization or molecular orbital theory be used to explain paramagnetism? For instance, when something is hybridized to make enough bonding electrons, do all the electrons end up ...
15
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1answer
5k views

How can the gauche-effect be explained?

Generally, anti-conformations are more stable. But in the case of 2-fluoroethanol, the gauche confirmation is more stable. It's given in March's advanced organic chemistry book that intramolecular ...
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1answer
1k views

How is a molecular orbital a 'quantum superposition' of the atomic orbitals?

Let me quote from Feynman's lectures the concept of superposition: (1)The probability of an event in an ideal experiment is given by the square of the absolute value of a complex number $ϕ$ which ...
3
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2answers
7k views

What do positive, negative and zero overlap of atomic orbitals mean?

I am confused about positive, negative and zero overlaps. Do they represent the extent of overlap or are they related to the bonding and anti-bonding orbitals as described in Molecular Orbital ...
5
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1answer
275 views

Stereochemistry of product in Diels-Alder reaction

I have a few questions on this problem I solved: 1) Why does carbon "b" on methyl vinyl ketone attack carbon "5" on the lactone? Why not carbon "2"? 2) The answer key says that the end product ...
6
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1answer
878 views

Axial vs equatorial attack of Grignard reagent on dioxan-5-one and dithian-5-one

How to account for the diastereoselectivety (axial vs equatorial attack) of these reactions?
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3answers
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How is hyperconjugation into antibonding orbitals stabilizing?

So I learned that hyperconjugation is electron delocalization from a $\ce{C-H}$ $\unicode[Times]{x3C3}$ bond into an empty p orbital (on a carbocation for example) or an antibonding orbital. I get how ...
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3answers
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Why is the inversion barrier larger in PH3 than it is in NH3?

The inversion barrier in $\ce{NH3}$ is approximately $5~\mathrm{kcal~mol^{-1}}$ and that of $\ce{PH3}$ is $35~\mathrm{kcal~mol^{-1}}$. This has well-known stereochemical consequences in that amines ...
3
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2answers
794 views

Rotational Barriers - Amide and Hydroxamic Acid

Why the barrier to rotation about the $\ce{C-N}$ bond higher in an amide than it is in a hydroxamic acid? (MO-based explanation preferred)
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343 views

QMOT | Orbital mixing in methyl

The following picture is from E. V. Anslyn Physical Organic Chemistry and shows constructing of MO of methyl using QMOT. MOs $\textbf{E'}$ and $\textbf{D'}$ are formed by mixing $\textbf{D}$ and $\...
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2answers
2k views

What is the highest known bond order?

In science we learn about single, double, and sometimes triple bonds. From a quick search I have found up to sextuple bonds. Is there a maximum bond order? If yes/no, what causes this?
5
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1answer
4k views

Structure of Buckminsterfullerene

In several pictures that I have seen of buckminsterfullerene and graphite (such as below), each carbon is bonded to only 3 other carbons, so it only forms 3 covalent bonds. I asked my teacher about ...
23
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2answers
9k views

Sp5 hybridization in cyclopropane?

I have never before heard/read about something as a $sp^5$ hybridization. Today, Henry Rzepa's blog post made me aware of the existance of such a bonding system. That made me search a little bit and I ...
8
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1answer
326 views

What happens to the complex part of the wave function when doing LCAO?

I understand that in general the wave function can take complex numbers, however when talking about combining atomic orbitals to form molecular orbitals we talk about the phase of the orbital being ...
7
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3answers
6k views

Does the shared electron in Covalent bonds revolve around nucleus?

We know that electrons are charges that revolve around the nucleus. Then, when in covalent bonds the electron is shared; does the electron obey the rule?
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0answers
48 views

Molecular Orbital Sequence [duplicate]

Two highly respected books: Atkins, Chemical Principles 5th ed. and Clayden Organic Chemistry 2nd ed. don't agree on the orbital arrangement of the $2p$ orbitals of $\ce{N2}$. Clayden on page 94 ...
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4answers
37k views

Why is the bond order of CO+ 3.5?

According to my books the bond order of $\ce{CO+}$ is $3.5$. But shouldn't it be $2.5$? On googling this, I found the following answer that is on Stack Exchange but its only talks about the bond ...
12
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1answer
416 views

What's the reaction type of the Hydrogen shift?

Rearrangement of cycloheptatrienyl carbene yields heptafulvene via a hydrogen shift. I see that the reaction is favorable because there is a conjugative effect with the $\pi$ system of the ring in ...
21
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5answers
10k views

Physical intuition behind negative values for wave function?

So a positive and a positive wave function create a bonding orbital where the probability of finding an electron is summed while a positive and a negative create an anti-bonding orbital with a lower ...
5
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1answer
1k views

Reduction of butadiene with Na/NH3 - stereoselectivity

Why is the major product of the reduction of butadiene with sodium in liquid ammonia cis-2-butene (60:40) when it is thermodynamically less stable than trans-2-butene?
3
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1answer
128 views

Carbon/Silicon pentacovalent intermediate during substitution

During $S_N2$ reaction with a silicon compound, a pentacovalent intermediate is formed, while there is no such intermediate formed with carbon compounds (only a pentacovalent transition state). Why is ...
7
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1answer
257 views

Geometries of methyl and silyl radicals

The $\ce{.CH3}$ radical is planar but the $\ce{.SiH3}$ radical is a trigonal pyramid. Why are they different? After all, $\ce{C}$ and $\ce{Si}$ are in the same group.
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1answer
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Orbital correlation diagram for the cleavage of cyclopropylmethylene carbene

In the last exam we were asked to rationalize the mechanism of the cyclopropylmethylene carbene cleavage into acetylene and ethylene. In the lecture we discussed pericyclic reactions (cycloadditions, ...
18
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2answers
102k views

Molecular orbital (MO) diagram for N2 and N2^-

I have been taught that the MO diagram is different for molecules with 14 or less electrons than the one used for molecules with 15 or more electrons. For $\ce{N2}$ the orbitals in increasing energy ...
20
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1answer
232 views

Similarities and Differences between Resonance and MCSCF treatments

Recently, there has been a question by Voldemort concerning different resonance structures of $\ce{NCO-}$, requesting an explanation why one resonance structure would be more preferred than another. ...
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2answers
1k views

Why is the resonance concept not required in molecular orbital theory?

In valence bond theory, resonance plays a pivoting role; why isn't such concept needed in MO theory? Why is it told that "MO theory provides a global, delocalized perspective on chemical bonding"? (...
33
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3answers
20k views

What is actually the difference between valence bond theory and molecular orbital theory?

Recently I have read about both of the concepts in my book (Physical Chemistry by Atkins, Paula). It was literally a reading; though I could understand the language and superposition of orbitals, ...
3
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1answer
227 views

Can one relate the frequencies of vibrational modes within a molecule to the molecule's HOMO/LUMO energies?

Can one relate the frequencies of vibrational modes within a molecule to the molecule's HOMO/LUMO energies?
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1answer
824 views

Singlet/triplet oxygen cycloadditions

Why can singlet oxygen participate in cycloaddition reactions while triplet oxygen, on the other hand, can't?
14
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1answer
875 views

How is spiro[4.4]nonatetraene antiaromatic

How is spiro[4.4]nonatetraene antiaromatic? I know that spiro compounds exhibit homoaromaticity, but how do they exhibit antiaromaticity?
6
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1answer
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Difference between oxygens in a carboxylic acid?

I've been reading about MO theory and am wondering if the traditional model of carboxylic acids is correct. Usually, how it's presented is that the carbonyl carbon is doubly bonded to one oxygen and ...
4
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1answer
440 views

What are good books about MO theory that don't require a lot of math background?

Are there any books about MO theory that explain the theory to a certain detail but don't rely on a lot of math background or explain the math within the book?
5
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2answers
476 views

How can hybrid orbitals be equivalent?

How can hybrid orbitals be equivalent? Take, for example, $\mathrm{sp^3}$ hybridization. The wave functions of each hybrid orbitals are given by: \begin{align} \psi_1 &= \psi_s + \psi_{p_x} + \...
8
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1answer
2k views

Is the hybridization only related to atomic orbitals but not to the molecular orbitals?

What is Hybridization? (Spelling: Hybridisation (British English) / Hybridization (American English)) The hybridization is a concept that describes atomic orbitals. In other words: Hybridization ...
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0answers
705 views

Is the para-position of anisoles more reactive than ortho in electrophilic substitutions?

In my group’s seminar last Friday, we discussed the total synthesis of 6-demethyl-6-deoxytetracycline 1 by Woodward et al.[1] One intermediate of their synthesis is meta-substituted anisole 2 that ...
9
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0answers
490 views

Free Web-Based Orbital Solver to look into the Walsh orbitals of a perturbed cyclopropane

There exists a free online orbital calculator. When I draw cyclopropane it plots three molecular orbitals, but unfortunately it doesn't use the Walsh orbitals. Are there any free online tools which ...
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1answer
1k views

Subtracting wave functions?

In molecular orbital theory bonding of two atoms can be seen as addition or subtraction of the wave functions of these atoms. Addition seems pretty logical and straight-forward - atoms overlap their ...
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1answer
3k views

Limitations of Lewis structures

Using Lewis structures to describe chemical bonds inside a molecule is still fairly common start in undergraduate education. Lewis structure however can be misleading, or just simply wrong in many ...
4
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1answer
918 views

Can I predict the preferred resonance structure of carbon monoxide from its molecular orbital scheme?

Because of the 8-valence electron rule I assume in CO the left resonance structure to be favored . $$\ce{:\!\overset{\ominus}{C}#\overset{\oplus}{O}\!: ~<->~ :\!C=O\!:: ~<->~:\!\overset{\...
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3answers
3k views

Are the bonding orbitals in methane equivalent - photoelectron spectrum

The low energy portion (the part dealing with the $\ce{2s}$ and $\ce{2p}$ electrons) of the photoelectron (PE) spectrum of methane is reproduced below. (image source) The reaction being examined is ...
18
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2answers
2k views

What does it mean when it is said that an sp³ orbital has 25% s character?

My textbook frequently mentions: $\mathrm{sp^3}$ hybrid orbital has 25% $\mathrm{s}$-character and 75% $\mathrm{p}$-character. What are these "characters"? And how do these characters influence ...
16
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1answer
2k views

Is azide paramagnetic?

Is the azide ion ($\ce{N3-}$) paramagnetic? How do I use molecular orbital theory to show that it is or isn't? I drew a sine wave diagram and filled up the $1\pi$ and $2\pi$ MOs, and since there ...
32
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1answer
38k views

What is a non-classical carbocation?

What is a non-classical carbocation? How is it different from a classical carbocation? I am confused as I have come across this term many times on Chem.SE but there seems to be nothing for my level ...