A method of studying bonds between atoms in which electrons' motions are defined as being all around the molecule, though influenced by nuclei.

learn more… | top users | synonyms (2)

2
votes
1answer
20 views

Formation of Bands in Semi-Conductors

At school, we are learning about semi-conductors and their applications in modern electronics. One of the features of semi-conductors is that there is a small energy gap between the valence and ...
3
votes
1answer
39 views

If I can't draw resonance structures for a pi system, does that mean it doesn't exist?

Whilst trying to answer this question I came across an interesting situation regarding the relationship between resonance structures and molecular orbitals. There are two places that you can ...
4
votes
1answer
32 views

Lowering energy in molecular orbital mixing

When drawing molecular orbital diagrams for mixing two orbitals we always end up with one orbital which is lower in energy than the initial orbitals and another which is higher in energy. The ...
8
votes
1answer
589 views

Why is the cyclopropenyl anion “Not Aromatic”?

Is the following compound "Anti Aromatic" or "Not Aromatic" ? The above compound contains a single ring, has conjugation and also has $4 \ (=4n)$ electrons. So, according to Hückel's ...
1
vote
1answer
96 views

What is the IUPAC name of this Di-Benzene like compound? Is it Aromatic?

What is the IUPAC name of this compound? Is it Aromatic? The above compound has $12 \ \pi$ electrons and according to Hückel's Rule, it should not be aromatic because $12 \neq 4n+2$, but it ...
-1
votes
0answers
22 views

learn chemical reaction at atomic level? [duplicate]

I read chemical reaction Before . It was like mix A and B with condition X and D is born.That was just lot of memorization.I need to know, why condition C,why other condition wont work, what other ...
1
vote
0answers
24 views

Molecular Orbitals of Hydrogen Fluoride (HF)

This source states that the three s-orbitals of hydrogen and fluorine interact to form three new molecular orbitals, while other sources say that the 2s orbital is non-bonding. Which one is more ...
1
vote
0answers
36 views

How do i make an molecular orbital diagram step by step?

My professor explained me, but i'm still unable to do a correct molecular orbital, for a diatomic molecule
7
votes
0answers
98 views

How to rationalise with MO theory that CO is a two-electron donor through carbon?

A question I am looking at is as follows: $\ce{CO}$ is isoelectronic with $\ce{N2}$. Sketch MO diagrams for $\ce{CO}$ and $\ce{N2}$. Point out key differences between the diagrams and use the ...
3
votes
1answer
75 views

How are the electrons of benzene actually configurated?

I found this diagram here: According to it, it is not true that the six electrons of carbons in the pi-orbitals above the ring are all identical. But, how can it be the case, seeing that this ...
0
votes
0answers
26 views

Why do ionisations from non-bonding orbitals result in little/no vibrational structure in a photoelectron spectrum?

I understand that ionisations from bonding and antibonding orbitals create vibrational structure from the Franck-Condon principle, resulting in a greater overlap integral between different vibrational ...
0
votes
0answers
35 views

Hybrid orbitals in molecular orbitals

In our textbook there are two topics that I can't make connection between: hybrid orbitals which (as I understand) are used to demonstrate the spacial shape of molecules like CH4 with VSEPR while ...
5
votes
1answer
66 views

Why is oxygen paramagnetic?

Paramagnetic molecules are molecules that have single electrons. When I draw the lewis structure of $\ce{O2}$, it appears to be a diamagnetic structure. What makes it paramagnetic?
1
vote
0answers
25 views

HSAB: alkyl halides & carbonyls LUMO energy flaw

Hard electrophiles have LUMO of higher energy than soft electrophiles. Alkyl halides are considered to be soft electrophiles while carbonyl compounds are considered to be hard electrophiles. The sigma ...
1
vote
1answer
74 views

How should I construct the orbitals of dilithium using only pen and paper?

For a week I have lessons about quantum chemistry and I have a trouble understanding how to arrive at the good answer for the drawing of the orbital $(\ce{III})$ for $\ce{Li2}$ (see the second ...
6
votes
0answers
55 views

How does spin flipping of triplet carbenes occur?

Below is presented a page from Clayden Organic Chemistry 2ed. How and why does the spin flipping during the collision with solvent molecules actually occur?
3
votes
0answers
50 views

Mechanism for the Cleavage of Diborane?

The cleavage of diborane was presented in a recent lecture, and it was said that the borane could be cleaved unsymmetrically if sterics allowed, or symmetrically if they did not, as shown in the image ...
12
votes
1answer
917 views

Why/how is blood red? (colours of hemoglobin)

Oxyhaemoglobin is red, deoxyhaemoglobin is bluish-purple, and carboxyhaemoglobin is a cherry red colour. Evidently in the porphyrin around the iron molecule in heme there is a conjugated pi system ...
0
votes
0answers
18 views

Why does conjugation decrease energy? [duplicate]

Why does an increase in the degree of conjugation in a molecule decrease the HOMO-LUMO gap?
2
votes
1answer
56 views

How does molecular orbital theory explain CH4?

I have understood the formation of $\ce{CH4}$ by valance bond theory, but I'm having trouble understanding it through molecular orbital theory. The energy level diagram of molecular orbitals of ...
0
votes
1answer
32 views

“Exactly Equal” and “At Least” in electron excitation

When we examine IR spectra, we see troughs corresponding to absorption at exactly a specific frequency that corresponds to the energy needed to stretch certain bonds (although translational motions ...
0
votes
0answers
9 views

Trends in Single Bond Enthalpy of All Nonmetal Groups

Here I have a list of single bond enthalpies, $\ce{X-X}$, in kJ/mol, for the nonmetals arranged by group: Group 7: F: 155 Cl: 242 Br: 193 I: 151 Group 6: O: 146 S: 266 Se: 172 Te: 126 ...
0
votes
0answers
59 views

How to find the bond order of molecules like BF3,SO3,NO2+

I know that the formula for bond order is 1/2*(Nb-Na).But is there a quite simpler way than to use this formula?As the use of this formula requires the writing down electronic config according to ...
3
votes
0answers
74 views

Negative hyperconjugation stabilizes tricyclopentane derivate

As far as I know, negative hyperconjugation means, that we have electrons that are transferred from a p- or $\pi$- to a $\sigma^*$-orbital. In the lecture, we analyzed a TMS-substituted ...
0
votes
0answers
47 views

Why is there only one nodal plane in σ* molecular orbitals for homodiatomic molecules?

I know that there's one nodal plane exactly inbetween the σ* MO however why is there not three nodal planes in total? As the picture shows three areas of zero electron density (one on each P ...
1
vote
1answer
90 views

Does crystal field splitting energy Δ increase going down a group of transition metals if the ligands are weak field?

Going down a group, the metal orbitals are more diffuse so there is greter overlap between the metal and the ligand orbitals. If there are no π-interactions, i.e. with σ-donor ligands like ...
1
vote
1answer
72 views

Structure of $\ce{HNO3}$ with Molecular Orbital diagram

Take an example, $\ce{HNO3}$ The total valence of $\ce{HNO3}$ must be 24. By using formula $\pi =6\mathrm{n}+2-\mathrm{V}$ where $\pi$ is number of $\pi$ electrons, $\mathrm{n}$ is number of atoms ...
4
votes
0answers
66 views

How are SN2 transition states stabilised by adjacent double bonds and carbonyl groups?

It is my understanding that transition states in an SN2 reaction have some filled and some empty orbital character, as we have the backside of the C-X σ* beginning to fill with electrons from the HOMO ...
0
votes
0answers
85 views

What does Molecular Orbital Theory get wrong?

I am learning about MO theory in my advanced inorganic chemistry course and am starting to realize that it is truly the most accurate representation of how molecular orbitals look like, where they are ...
1
vote
0answers
35 views

mechanism in Birch reduction

at first I wondered why 2 H are added to opposite side of benzene like reaction below. because I could imagine 2 H added right next to each other or 1 C away from each other. so, looking for ...
3
votes
1answer
46 views

What is the criterion for filling up of electrons in molecular orbitals of increasing energy in simple diatomic species?

So far I have found different ways in different books. For e.g. One says "In MO electronic configuration of diatomic species up to 14 electrons, $\sigma2p_z$ orbital (considering $z$ as the ...
6
votes
0answers
53 views

Orbital and state correlation diagram for ring-closure of pentadienyl to a cyclic allyl

This is an exam question. I am to construct the orbital and state correlation diagram for one of the reaction below (disrotation or conratation). Also, I should explain whether the reaction is ...
0
votes
0answers
66 views

How do energy levels work in relation to HOMO, LUMO transition?

I've just started a basic quantum course and I'm facing many exercises regarding the transition from HOMO to LUMO. I've already mastered unidimensional problems, but I'm a bit confused in ...
0
votes
0answers
31 views

What does a molecules color have to do with its bond/orbital energies?

For example, elemental iodine is deep violet. It's sigma bond or perhaps the lone pairs are capable of absorbing all visible light frequencies except violet which is why we see it as that color. ...
1
vote
0answers
52 views

Why is tin(IV) iodide bright orange while elemental iodine is violet?

Does it have anything to with iodines polarizability? Is there a way to explain this using sigma bonding or an MO diagram?
1
vote
1answer
85 views

Confusion about atomic/molecular orbital terminology

I have come across several different orbital terms: atomic orbitals, natural orbitals, split-localized orbitals, molecule-intrinsic orbitals, quasi-atomic orbitals. I don't know what the difference ...
1
vote
0answers
63 views

Why is He2- unstable?

$\ce{He2-}$ according to MO theory should be possible with one electron in 2s sigma, but my professor said only at very low temperatures for some reason. Why only at low temperatures? What is the ...
1
vote
0answers
36 views

Anti-bonding orbitals for ionic bonds

Are there any concept of Bonding and Antibonding orbitals in the case of Ionic bonds, as there are in case of covalent bonds (electron sharing) ? OR: Is it possible to break an ionic bond by pushing ...
3
votes
0answers
70 views

Wavefunction convergence error and keywords. (Spartan)

I am currently working with Spartan software and am calculating MOs. My problem is that when I try to do calculations SCF error occures. And every time I try to put some keywords (like CONVERGE, ...
4
votes
0answers
31 views

How are the hydrogens attached to the nitrogen atom in the ammonium ion?

Naively attaching hydrogens to a nitrogen atom's electron orbitals results in a picture like this: However, there are two problems with this drawing that I can see. First, I have heard that the ...
0
votes
0answers
22 views

Determining the type of electrocyclic via MO theory

I have been working on this particular problem for a while now to determine how this particular reaction plays out. I think it is a a thermo electrocyclic ring transformation involving 6 pi ...
4
votes
1answer
80 views

Ordinary differential equation for molecule collision

My knowledge is 0 in chemistry. But, I have a good background in mathematics and computer programming. I have planed to simulate the collision of two simple molecules $\ce{Br2}$ and $\ce{H2}$ just ...
5
votes
2answers
112 views

Why HF is said to be formed from H-1s and F-2pz overlap?

According to Wikipedia, HF is formed by the interaction between hydrogen's $1\mathrm{s}$ orbital and fluoride’s $2\mathrm{p}_z$ orbital: In hydrogen fluoride HF overlap between the H 1s and F 2s ...
0
votes
0answers
19 views

Can you deduce unsaturated fatty acid structure from orbital hybridisation theory?

In biology class we have seen how an unsaturated fatty acid has a double carbon bond which makes the molecule bend. In chemistry class we have seen orbital hybridisation theory and as an exercise I ...
2
votes
0answers
133 views

Why does AsH5 not exist?

Why does $\ce{AsH5}$ not exist? Is it because the s-orbital of H doesn't and can't overlap with the d-orbital of As after As makes $\rm sp^{3}d$ hybridization?Theoretically the bond can occur because ...
1
vote
1answer
68 views

How to compare the energies of sigma and pi bonds in molecular orbitals of diatomic heteronuclear species?

There is a rule for diatomic homo-nuclear species that says that if $Z<8$ then $$E(\sigma_{2p})>[E(\pi_{2p_y})=E(\pi_{2p_z})]$$ and the inverse if $Z\geq8$ and in both case we have energy of ...
2
votes
0answers
94 views

Why is conjugation not possible if there is not present alternate $\pi$ molecules according to MO theory?

I was reading this page at Chemwiki; there they were discussing conjugated-$\pi$ bond. In order to show that conjugation requires alternate double bonding, they cited the example of ...
11
votes
1answer
149 views

Jahn-Teller Distortions in Square Planar Complexes?

A Jahn-Teller distortion is predicted whenever a non-linear symmetric molecule has degenerate orbitals and has unequal electron occupation in those degenerate orbitals. Of course this most often is ...
4
votes
1answer
61 views

Is it possible to have accumulation of electron density in the inter-nuclear region even if the overlap integral is zero?

Recap: Lately, I've been studying Hückel theory where I learned about the approximation of neglecting all overlaps and making overlap matrix an identity matrix that is $S_{AB}= 0\;_; \;S_{AA}= 1$ or ...
8
votes
2answers
190 views

How can off-diagonal Hamiltonian matrix elements be nonzero when the overlap matrix is diagonal?

While studying about Hückel theory, I got accustomed to the approximation of making the overlap matrix an identity matrix; that is making the off-diagonal elements zero as $S_{AB}= S_{BA}= 0\;;$ this ...