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1500 questions
17
votes
2 answers
Is the triplet state of the cyclopentadienyl cation really aromatic?
While checking the ASAP articles of the Journal of the American Chemical Society I came across a very interesting contribution by Costa et al. who synthesised a $\ce{BF3}$ stabilised cyclopentadienyl cation 1 and confirmed that its singlet state was…
Jan
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17
votes
2 answers
Why is crystallography still used in some cases for small molecule structure determination?
I was wondering for some time why in some cases x-ray crystallography and not NMR is used for structure determination of small molecules? Does crystallization maybe require a smaller amount of the compound than NMR?
geox19
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17
votes
2 answers
Practical differences between storing 2-electron integrals and calculating them as needed?
Some texts that I read suggest calculating all of the 2-electron integrals at once (taking into account permutational symmetry) and some suggest calculating them on demand when building the Fock matrix.
Which of these is the most computationally…
obackhouse
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17
votes
2 answers
Predicting sigma bond overlap strengths of s-s, p-p, s-p, sp-sp etc
How can we qualitatively predict $\sigma-$bond strengths of overlap between:
$\ce{s-s}$
$\ce{s-p}$
$\ce{p-p}$
$\ce{sp-s}$
$\ce{sp-p}$
$\ce{sp-sp}$
etc.?
My school-book says $\ce{s-s}$ overlap bond strength is greater than $\ce{s-p}$ overlap which…
jonsno
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17
votes
1 answer
Hellmann-Feynman Forces with Hartree-Fock
The energy in the Hartree-Fock approximation is given as:
$$E_{HF}=\left<\psi_{HF} \left| \hat{H} \right| \psi_{HF} \right>=\sum_{i,j}P_{i,j}H_{i,j}^{core}+\frac{1}{2}\sum_{i,j,k,l}P_{i,j}P_{l,k}(ij||kl)+V_{NN} \tag{1}$$
The geometrical derivative…
Erik Kjellgren
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17
votes
1 answer
How to name this quintuply-bonded chromium dimer?
Depicted below is a chromium compound with a metal–metal quintuple bond. It boasts two identical bridging ligands, derivatives of 1,3-diphenylbenzene. The aim of this question is to figure out
the proper name.
Proper means without losing…
Linear Christmas
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17
votes
2 answers
What happens to electrons in metal complexes after excitation by visible light?
My book writes:
When white light shines through a solution of a complex ion of a transition metal, photons of a particular frequency are absorbed and their energy promotes an electron from lower energy level to upper energy level. We perceive the…
Eliza
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17
votes
1 answer
Are there any significant uses of the compound formed by magnesium and anthracene?
In an unusual reaction, magnesium reacts with anthracene in THF to form a grignard-like compound called, prosaically, magnesium anthracene:
I remember using it briefly in the 1980s. At the time there was speculation about its potential use in both…
matt_black
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17
votes
2 answers
Why are fluoroalkyl chains hydrophobic/oleophobic?
I'm searching for an answer that explains the hydrophobicity / oleophobicity in terms of intermolecular forces, but can't really find one.
Below is an example fluoro-alkyl nano-particle, F-POSS. It has 8 ligands of a fluoroalkyl chain…
John Snow
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17
votes
1 answer
Molecular orbital diagram for BF3
I'm trying to build a molecular orbital diagram for BF3 and I'm running into problems with irreducible representations on the F side.
2s for B has an irreducible representation of A1. 2p for B has an irreducible representation of E' and A''2.
2s…
Billqaz3
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17
votes
4 answers
Why is the electron-nucleus attraction modelled with only electrostatic interactions?
While reading about the structure of an atom, I've encountered (even in some renowned books) the statement that electrons and nuclei are attracted due to electrostatic, or Coulombic, attractions.
However, since the charged particles (electrons and…
Abhinav Dhawan
- 297
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17
votes
1 answer
How does WD-40 remove rust?
One of the often-touted uses of WD-40 is that it "dissolves rust". The official website states that WD-40 "breaks down the bonds between metal and rust".
I can't understand how this would work, since there seem to be no rust-dissolving ingredients…
Maarten
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17
votes
6 answers
Why do we need the identity operator, E
In group theory, in order to assign a point group, one must first identify the symmetry elements present in the molecule.
To give an example, water has:
a rotational axis, labelled C2 since it is a two fold axis, with a π/2 rotation giving back…
NotEvans.
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17
votes
1 answer
Conventional heating compared to microwave heating of chemical reactions
In order to try to increase yield of my cross-metathesis, it was suggested to carry out the reaction in the microwave (a lab microwave, not a kitchen microwave).
The rationale for this was that microwaves accelerate the reaction, but thinking on…
James Dealon
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17
votes
3 answers
What is the mechanism of action of anaesthetics?
A range of very different compounds are used in medicine as anaesthetics. They don't seem to have much in common chemically but they all seem to keep people asleep while medics are doing nasty things to them.
Inhaled anaesthetics include a variety…
matt_black
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