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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What are the details of being able to predict whether a pi or sigma bond will be lower in energy for diatomics (or any system for that matter)? [closed]

I have heard that one can find out the ordering of pi and sigma orbitals (such as the switch between N2 and O2 in their MO diagrams) using quantum mechanical calculations. I am a research student with ...
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1answer
107 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 ...
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1answer
49 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?
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1answer
29 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 ...
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1answer
66 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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141 views

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 ...
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2answers
105 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 are: $(\sigma 1s)( ...
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43 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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90 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"? ...
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5answers
417 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, ...
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1answer
93 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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111 views

Singlet/triplet oxygen cycloadditions

Why can singlet oxygen participate in cycloaddition reactions while the triplet oxygen, on the other hand, can't?
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160 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?
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1answer
83 views

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
85 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?
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2answers
74 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} + ...
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1answer
160 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 is an ...
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46 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 ...
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49 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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91 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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87 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
72 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\!:: ...
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2answers
188 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 ...
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243 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 ...
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82 views

Is azide paramagnetic?

Is an azide ion paramagnetic? How do I use MO theory to show that it is or isn't? I drew a sine wave diagram and filled up the 1pi and 2pi MOs, and since there is no unpaired electron, can I ...
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1answer
521 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 ...
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1answer
79 views

Torquoselectivity: Disrotatory ring opening

In organic chemistry lecture we discussed the beginning of the Woodward Hoffmann Rules with a key step of the vitamin B12 synthesis. (The initial paper from their work can be found here: ...
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219 views

How can the dipole moment of carbon monoxide be rationalised by molecular orbital theory?

Despite the fact that oxygen is much more electronegative than carbon, the bond in $\ce{CO}$ presents a weak dipole moment. This observation can easily be explained using the concept of "dative bond", ...
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82 views

Molecular orbitals of CH2 an SLACs

I was wondering about molecular orbitals of methylene different states 1B1 3B1 1A1 and how are they connected to symmetry point group lower case 1a1, etc orbitals what those numbers and alphabets ...
2
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1answer
71 views

Understanding FHF- molecular orbital diagram?

I need help understanding the molecule FHF-'s molecular orbital diagram: So I know that "ag" refers to the 2pz and 2s orbitals of fluorine atoms...but I am not sure why "ag" is labeled for the ...
2
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1answer
43 views

MO for $N_2^{2-}$

Could someone please show me the MO diagram for $\ce{N_2^{2-}}$? What I did was since N has 5 valence $\ce{e^{-}}$, then $\ce{N_2}$ must have 10, and $\ce{N_2^{2-}}$ must have 12. And $\ce{N}$ has $s$ ...
4
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1answer
63 views

Why does iodine have different colors in different media?

It is violet in trichloromethane, but brown in water. why? In the Shriver Atkins book, they tried to explain this using Molecular Orbital Theory which was not clear to me
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44 views

Orbitals involved in Ni(CO)₄

Which orbitals are filled? Is it diamagnetic? According to CFT, $\ce{CO}$ is a strong field ligand, so will it pair the electrons and be diamagnetic?
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3answers
442 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?
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180 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
101 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
59 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?
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2k 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 ...
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1answer
370 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 ...
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4answers
245 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 ...
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1answer
46 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
363 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
53 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
116 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 ...
5
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1answer
209 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 ...
7
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2answers
598 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?
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2answers
964 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 ...
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1answer
1k 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
837 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 ...
5
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1answer
86 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 ...