For questions seeking generalised answers deduced from or composed of theories regarding the chemical reactions involved.

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2
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0answers
61 views

What is the pKa of the oxonium / hydronium / H3O+ ion?

Although the wikipedia page on Hydronium indicates a pKa of -1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:Hydronium#pKa.3F) ...
1
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1answer
20 views

How to estimate the dielectric constant of a liquid?

Are there any approximate relationships between the (static) dielectric constant of a liquid and properties of the individual molecules? For example, suppose I know the polarizability and dipole ...
4
votes
1answer
132 views

Why are excited Slater determinants used to describe electron correlation?

Usually the first step in describing the electronic wave function of a molecule or atom is to describe it with a single Slater determinant. I get that this is an independent particle approximation, ...
2
votes
2answers
73 views

How to properly denote imaginary magnitudes of vibrational frequencies

Vibrational frequency computations provide the magnitudes of vibrational frequencies for each vibrational mode of a molecule ($3N-6$ degrees of freedom for non-linear molecules and $3N-5$ for linear ...
1
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1answer
30 views

Polymers with no molecular mass distribution?

What sort of ideal conditions are required - theoretically - to conduct polymerization reactions to make all the macromolecules end up with exactly the same molecular mass, just like the products in ...
0
votes
1answer
75 views

Software for predicting chemical reactions

I wondered if it was possible to predict the product(s) of a reaction (or even the equilibrium) based on the reactants and the temperature/pressure. I found an answer to a similar question here: ...
2
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0answers
71 views

DFT optimization of a molecule in gaussian and find electrophilic sides [closed]

I am not a pro, but I have some experience with gaussian. For example, I can optimize a structure, calculate the frequency and rotational energies. In the lab I made a nucleophilic substitution ...
4
votes
1answer
137 views

Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable ...
0
votes
1answer
75 views

Configuration Interaction matrix composition from electronic configurations

The six electronic configurations below could all be found in the matrix elements of the CI matrix at CISD level. How do I construct the 6 x 6 CI matrix composed of these six configurations and which ...
2
votes
1answer
56 views

Equilibrium: Equations with complex roots

I'm studying civil engineer in my first year. We have a course called "General Chemistry". One of the chapters was about chemical balance of a reaction (called equilibrium in English, I think). We got ...
8
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0answers
119 views

Is there a general consensus on the causes of the $\alpha$-effect?

There have been various explanations posited for the $\alpha$-effect. It is currently in the list of unsolved problems in chemistry on Wikipedia, but, due to a lack of references to that effect, I'm ...
1
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1answer
67 views

Electrode potentials at interfaces?

My questions relates to the fundamental concept of electrochemistry, more specifically the electrode potentials. 1) First, why is there a potential difference at the interface of two phases? ...
2
votes
2answers
76 views

Do ions also form special electron configurations? (just as Copper and Chromium do)

Do ions also form special electron configurations? (just as Copper and Chromium do) I know that because copper has 1 electron in its s-orbital (highest) because it wants to have a full d-orbital ...
5
votes
1answer
93 views

Computing of strengthening of pi-interaction

I need some practical advise. What would be the easiest approach to compute strengthening or weakening of pi-interaction in a bond with multipole-bond character. I'm not really fond of going through ...
2
votes
1answer
449 views

Why is a theoretical titration curve higher than a practical one?

I'm currently in high school and I did two titrations. The first one is a titration of $10.0$mL $0.1$M $\ce{HCl}$ with $x$ mL $\ce{NaOH}$. I obtained the following titration curve: The blue curve ...
1
vote
2answers
1k views

what is a pseudohalogen/pseudohalide?

What do you mean by a pseudohalogen/pseudohalide and how do you tell whether a molecule/ion is a pseudohalogen/pseudohalide ?
1
vote
1answer
282 views

What does reaction exothermicity say about the stability of molecules

If a reaction is exothermic it means that the energy state of the products is lower than that of the reactants so this will be the state that 'nature' will naturally strive for. Often you see that ...
1
vote
1answer
724 views

Why x in equilibrium calculations can be “ignored”

You don't need to work out anything for me. I am just giving an example so you can explain something to me. For example: $$\ce{ClF3(g) <=> ClF(g) + F2(g)}\\ \ \ K_c=8.77\times10^{-14} \ \ @\ ...
5
votes
1answer
675 views

Electron density definition of single, double, triple bonds?

I was reading this question and the answer by @EricBrown to it and this got me thinking about covalent chemical bonds. The way I was always taught is that a single bond contains 2 paired electrons, ...
1
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1answer
267 views

Difference between the terms “autocatalysis” and “(branching) chain reaction”

Is there a technical difference between the terms "autocatalysis" and "branching chain reaction"? They both seem to refer to something very similar, namely sequences of reactions in which one of the ...
1
vote
1answer
35 views

Can I deduct heteronuclear van der waals parameters from homonuclear parameters in a forcefield?

I got a forcefield (OPLS-AA in this case) that lists lennard-jones parameters for all homonuclear van der waals interactions. Is there a way to deduct the heteronuclear vdw-interaction parameters from ...
6
votes
2answers
190 views

Measuring Thermodynamic Stability

We can predict whether a reaction can occur spontaneously by calculating the change in Gibbs' free energy. I was just wondering whether there is any general measure of the thermodynamic stability of ...
1
vote
1answer
119 views

Hot and cold air interaction in a sealed environment

What would happen if air heated to 1200 degree's Fahrenheit in a sealed environment was injected with colder air? No specific pressure defined yet just a general idea of potential interaction between ...
1
vote
0answers
164 views

Calculation of partial charges and protonation/deprotonation states depending on pH

What is the best method for calculating partial charges and protonation/deprotonation states of a small molecule such as phenol or caffeine, depending on the pH? For instance, it is well known that ...
9
votes
1answer
138 views

Are chiral quasicrystals possible?

Quasicrystals are materials that have long-range atomic order but lack the translational symmetry of conventional crystals. All quasicrystalline tilings and packings I have read about thus far, whilst ...
8
votes
4answers
1k views

Which chemical properties make the substance to be explosive?

I know that some chemical substances are used as explosives. The most famous maybe are nitroglycerin in dynamite and cyclonite in C-4. But which chemical properties (well physical don't play the role, ...
3
votes
1answer
240 views

Influence of solubility at different pHs on the complexation constants

Given some small chemical compounds whose solubility varies with pH, and in the case of compounds that can form complexes, I have seen that the complexation constant varies with pH. I think there ...
4
votes
1answer
66 views

How do chemists find a procedure to produce a given substance?

How do they find out exactly what reactions they can use to produce some substance they want to produce? Is there some reaction database that helps them find a way to make the target substance out of ...
3
votes
1answer
56 views

How can you estimate how much of a substance will dissolve in a given lipid?

How can you estimate how much of a substance with a known partition coefficient and other physical/chemical data regarding the substance will dissolve in a given lipid? In particular I would like to ...
2
votes
1answer
91 views

Questions about intramolecular interactions in AMBER forcefield

I am trying to run a molecular dynamics simulation with AMBER forcefield. However, it's the first time I use is, and while I know the form of the various intra- and intermolecular energy terms, some ...
4
votes
1answer
87 views

Could you estimate the rate of reaction from the chemical structure of the reactants? If so, how?

Say you have two compounds with their own unique chemical structures and you know the environment (e.g. temperature, pressure, presence of enzymes) could you then, using this information, approximate ...
3
votes
1answer
78 views

Is it possible to estimate a substance's water solubility from data like the substance's partition coefficient, dissociation constants, etc.?

If it is possible, how would you estimate a compound's water solubility from data like its partition coefficient, $ \log P $, its dissociation constant, $pK_a $, its molar mass, etc.?
4
votes
2answers
179 views

Basis sets that can be used for macrocyclic complexes

What could be the possible basis set that can be used for a metal base macrocyclic complex in gaussian09? I am using transition metals such as $\ce{Ni}$, $\ce{Co}$, etc. Also, I have tried using ...
1
vote
1answer
201 views

How does simulation software work at a fundamental level?

There are lots of software packages like Schr­­­ödinger Maestro or Argus Lab, which are used for simulations of docking. I have always been fascinated as to how such software works. What is the ...
1
vote
2answers
320 views

deduce chemical properties of a compound from elements

If we know the properties of two elements e.g Oxygen and Hydrogen. We know the following properties sound speed boiling point melting point refractive index etc. given that information, is it ...
0
votes
1answer
74 views

Methods: Does failing at intermolecular properties mean the same for intramolecular properties?

Let us consider the following: 1.) Method X fails at describing intermolecular non-covalent interactions. 2.) Method X excels at describing molecules of type Y. 3.) Method X ___?___ at describing ...
4
votes
2answers
115 views

Modeling perturbations of a quantum mechanical system

I'm wondering how to properly perturb a quantum mechanical system. I'm looking for a way to express the return to equilibrium of such a perturbed state, where the perturbation is in the Hamiltonian. ...
5
votes
1answer
170 views

Algebra of conserved quantities for chemical reactions

So there is the standard formation enthalpy $\Delta H^0_f$ and there is also formation entropy. Are there more (independent) quantities? What about the heat capacity? Is there a general theoretical ...
23
votes
2answers
2k views

Bonding in C2, a carbon-carbon quadruple bond?

Carbon is well known to form single, double, and triple C-C bonds in compounds. There is a recent report (2012) that carbon forms a quadruple bond in diatomic carbon, $\ce{C2}$. The excerpt below is ...
11
votes
2answers
326 views

How should I go about picking a functional for DFT calculations?

I've been looking to use time-dependent density functional theory, but reading the literature I keep getting overwhelmed by how many different functionals there are. How should I go about selecting ...
6
votes
1answer
826 views

What does “reaction coordinate” mean?

I'm familiar with the concept of a reaction coordinate from high school chemistry as some generic conformational parameter that all of the intermediate states of a chemical reaction lie upon. ...
6
votes
1answer
109 views

What does the charge distribution around a Stone-Wales defect look like?

I'm reading a book on carbon nanotubes (P.J.F. Harris, Carbon Nanotube Science, to be specific) at the moment and puzzling about Stone-Wales or 5775 defects. This is where two adjacent carbons undergo ...
6
votes
2answers
244 views

Z-matrix of a series of 5 colinear atoms

How can I write a Z-matrix for the following complex? O==C==O H--O \ H I have managed to write: ...
9
votes
1answer
854 views

Definitions of autocatalysis

Is there a formal definition or algorithm that can take a list of reactions and tell me whether it contains a set of species that can produce itself autocatalytically? It is clear that the following ...
11
votes
3answers
362 views

What is natural bond orbital theory used for?

My understanding is that the NBO methodology transforms the molecular orbital picture of a molecule into a collection of pairwise interactions (bond orbitals). This is obviously handy for didactic and ...
5
votes
1answer
190 views

Are buckminsterfullerene-corannulene complexes actually stabilised by π stacking?

According to wikipedia and the references given therein, $\pi\cdots\pi$ stacking interactions are the result of interaction between the quadrupole moments of two aromatic rings, rationalising the ...