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

learn more… | top users | synonyms

2
votes
1answer
24 views

Determining the boiling point of a substance with the triple point and critical point

If I have the pressure and temperature of a substance in its triple point, as well as its pressure and temperature in the critical point, how can I determine de boiling point of the substance at 1 atm ...
5
votes
1answer
57 views

Behaviour of element 111

Is element 111 considered to act as an eka-aurum? Being under the same column of group 11, which usually provides enough evidence for correlation of properties for an eka-element, would this element ...
6
votes
1answer
38 views

Collisonally induced intersystem crossing

What makes a molecule a good initiator of collisionally induced ISC? $\ce{N2}$, $\ce{O2}$ and $\ce{CH4}$ have been mentioned as examples. I imagine the most important factor is the ability to quench ...
3
votes
1answer
47 views

Possible Synthesis of a Polymer

Following a question I have asked previously, what I intend to inquire this time is quite similar as well, except, with a polymer. So previously I asked whether such monomer PCDO is possible to ...
6
votes
1answer
268 views

Born-Oppenheimer adiabaticity

Born Oppenheimer aproximation is said to be adiabatic. What does adiabatic mean? What would be the case of a non adiabatic approximation to the Schrödinger equation?
11
votes
2answers
413 views

Ripping apart a polymer - reaction or not?

I was holding a piece of plastic earlier, and I ripped it in half. This caused me to start to think about what was happening at the atomic level. If the plastic is being ripped, clearly bonds are ...
11
votes
2answers
444 views

For a given element do heavier isotopes form stronger bonds than lighter isotopes?

I know that $\ce{C-D}$ and $\ce{C-T}$ bonds are stronger than $\ce{C-H}$ bonds, but is this generally true for isotopes of all elements? (By isotopes I mean stable ones with large half lives.)
6
votes
2answers
168 views

Exchange-correlation hole

I did a google and chemistry.exchange search and found several technical definitions of the exchange correlation hole. The questions that I want to proposes are: What the exchange-correlation hole ...
7
votes
2answers
76 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", ...
7
votes
0answers
41 views

Radiation in space and its effects on chemical reactions?

I know that one current area of research is ways to protect astronauts from ionizing radiation when they venture out of the atmosphere of Earth, but would that same ionizing radiation be a cause of ...
3
votes
0answers
44 views

theoretical model for the Hydrogen bond

I am curious how from the perspective of quantum chemistry the Hydrogen bond is modeled. In particular I am interested in using such a model to estimate the amount of energy released per $\ce{H2O}$ ...
3
votes
2answers
180 views

What kind of math should I expect in first year chemistry?

The course calendar for my university describes Chem 101 and 102 as "math intensive". However, it doesn't say what kind of math is involved. What kind of math should I expect in first year chemistry? ...
5
votes
1answer
78 views

Acidity of unsaturated five membered ring relative to seven membered analogue

Which of the following is more acidic? The most acidic proton is positioned on the carbon that is at the top of the above drawings (the methylene hydrogens) on each of the two species as ...
2
votes
0answers
18 views

What would be the Slater's determinant of an excited state? [migrated]

Setup Introducing this spinorbital notation: \begin{align} \Psi_1=\chi_{(r1)}\alpha_{(\omega1)} &= 1 \\ \Psi_1=\chi_{(r1)}\beta_{(\omega1)} &= \bar{1} \end{align} and the Slater's ...
4
votes
1answer
36 views

Charge consistency in fragment qm/mm methods

I'm calculating the multipole moments on several fragments of a molecule. What are some procedures to ensure that the charges etc are representative of the complete molecule? How do I ensure I'm not ...
5
votes
0answers
35 views

How could you predict degenerate pi molecular orbitals just knowing what symmetry point group a molecule belongs to?

If you were to apply the Huckel method to some molecules which belonged to, say, $C_{2v}, D_{2h}, $ and $ D_{4h}$, which ones would you expect to have degeneracies? I'm not sure if this is mixing up ...
14
votes
1answer
156 views

What is the relation between surface tension and initial molecular harmonic?

Initial harmonic is measured as Hartree/Bohr^2 ( like IHarmonic=n in Gaussian Software ). As I am from physics background I am used to look at features from their dimension point of view: Actually ...
9
votes
2answers
108 views

Hypervalency and the octet rule

I realize that the octet rule is more a suggestion than a rule, and that it applies mainly to non-transition metal compounds. Still, compounds that don't have an octet, like $\ce{BH3}$, tend to ...
2
votes
1answer
174 views

Why are 2 ways to calculate the energy of the ground state?

Setup I found in Szabo, Quantum chemistry page 88, these two ways to calculate the energy of the ground state: $$E_0= \sum_a^N \langle a|h|a\rangle + \frac{1}{2} \sum_a^N \sum_b^N \langle ...
2
votes
2answers
51 views

Does the third law of thermodynamics apply to all compounds and elements?

According to wikipedia, the third law of thermodynamics is "The entropy of a perfect crystal, at absolute zero (zero kelvins), is exactly equal to zero.". Then, theoretically, could all substances, ...
8
votes
3answers
178 views

How to define custom force in quantum chemistry packages?

I dont know if this is really applicable but I want to add a custom force ( say F(x,y,z) ) to some atoms in my geometry optimization. Is there any way to add such forces to the DFT or Molecular ...
2
votes
1answer
31 views

CASTEP Geometry Optimization Movie

I am using a calculation software called CASTEP, within Materials Studio, and I want to make a "movie" of my geometry optimization, but don't know how to. CASTEP allows one to do many many different ...
7
votes
1answer
44 views

How to visualize or think about spin waves (magnons)?

According to Wikipedia: "A magnon is a quasiparticle, a collective excitation of the electrons' spin structure in a crystal lattice." I have little pictures in my mind for other quasiparticles. For ...
7
votes
1answer
84 views

PBP vs TBP geometry?

Why are the axial bond lengths greater than those of the equatorial bonds in a trigonal bi-pyramid (TBP) geometry molecule; but the opposite is true for pentagonal bi-pyramid (PBP) geometry molecules? ...
3
votes
0answers
68 views

Calculate the number of moles of NO₂ (g) produced per hour per liter of air?

A reaction of importance in the formation of smog is that between ozone and nitrogen monoxide described by $\ce{O3(g) + NO(g)->O2(g) + NO2(g)}$ the rate law for this reaction is: rate of ...
10
votes
2answers
221 views

How to find the second order perturbation to wave function?

Today, I'm looking for how to find the 2nd perturbation to the base in Rayleigh Schrödinger Perturbation Theory (RSPT). SETUP Starting from the 2nd order perturbation in Dirac's notation: ...
2
votes
1answer
48 views

How to get a protein's dihedral angles ordered by variance?

The setting: I want to simulate protein docking and let some dihedral angles vary, but in order to keep it low-dimensional I have to select those which are most likely to change. What I've thought of ...
15
votes
1answer
162 views

What would follow in the series sigma, pi and delta bonds?

I realise, that this question is a stretch, but I was wondering, how would a bonding orbital be called if it was formed from two $f_{x(x^2−3y^2)}$ or $f_{y(3x^2−y^2)}$ orbitals. Have there been any ...
1
vote
1answer
86 views

Is this a possible explanation as to why sigma bonds are stronger than pi bonds?

Sigma bonds form due to the axial overlap of two orbitals whereas pi bonds form due to their lateral overlapping. Since the former is more effective, we can say that sigma is stronger than pi. We mean ...
2
votes
2answers
94 views

Can we really beat the speed of light? [closed]

This is a rather physics question but I wanted to get an insight from a chemistry perspective. I heard from some that you can beat the speed or go faster than it but is that really true. Physicists as ...
4
votes
2answers
282 views

Why are sp hybridized carbocations high energy?

You don’t see carbocations on double bonds very much, and here’s a good reason: compared to sp3, there is more s character in the orbitals, so the empty orbital is held more closely to the ...
6
votes
4answers
119 views

Is there a field of chemistry that doesn't do experiments?

In other words, a field of chemistry that is all theoretical? I have heard of theoretical chemistry, but my chemistry professor said you can't really major in theoretical chemistry. He said the ...
6
votes
2answers
274 views

London dispersion forces and distance relationship

Why is the London dispersion force inversely related to distance but not to the second power but the sixth power? Why is there not an inverse square relationship as there is for Coulombic forces? Is ...
1
vote
0answers
39 views

Reducing NOx with Ammonia. Practical in a gasifier?

Sorry if this is an outright stupid question. I am no chemist. For nitric oxide: $\ce{2{NH_{3}} + 2 NO -> 2 {N_{2}} + {H_{2}} + 2{H_{2}O}}$ For nitrogen dioxide: $\ce{2{NH_{3}} + 2{NO_{2}} ...
1
vote
1answer
27 views

What are the possible concentration pathways for a 3-species system?

Inspired by this question, which asks if a multi-species system could oscillate around its equilibrium, I thought about the possible concentration pathways the following more narrow specified system ...
1
vote
3answers
63 views

Why do molecular orbitals in solids merge to bands?

Why do molecular orbitals in solids merge to bands? For example: In silicon every atom is sp3 hybridised, but when I merge two of these orbitals then it yields a bonding and an antibonding MO. When a ...
3
votes
1answer
74 views

Unitary Transformation of the HF equations

I am working on a code to preform a HF procedure and I am a bit confused about the unitary transformation of the basis. My instructions are as follows. specify the basis and geometry (done) ...
1
vote
0answers
54 views

How can I contribute to the chemistry with mathematical theories?, what kind of math is most used in chemistry? [closed]

I'm curious in how mathematics can contribute to chemistry. I know that in theoretical chemistry is very useful the Group Theory and Symmetries. If I'm wrong in something, please let me know. By ...
1
vote
1answer
187 views

Does the ammonium ion hydrogen bond with water?

What about oxonium ions, such as hydronium ion? Do these hydrogen bond with water? If we see hydrogen bonding as a purely electrostatic phenomenon, then why not? Ammonium ion still has nitrogen ...
0
votes
1answer
94 views

Molecular Orbital Theory and No. of bonds

The order of filling of molecular orbitals $\ce{O2}$ by MOT is this : But from it, how can I deduce that there is one sigma and one pi bond in an oxygen molecule ?
6
votes
2answers
85 views

Dissociation of water into H+ and OH-: Does the law of mass action hold at nanoscale?

Suppose water under neutral conditions is confined in a virtual spherical nanocontainer with a radius of 25 nm. To calculate the number of hydronium ions, one uses water dissociation constant which is ...
1
vote
1answer
54 views

Elastic scattering of x rays in 3D: the principle for XRD analysis

I have some trouble visualising scattering of x-rays in 3D, since all textbooks and examples present it in 2D. Under I will share some reflections (no pun intended) about the elastic scattering of x ...
7
votes
2answers
224 views

Carbon-Sulfur Bond Lengths; Resonance Effects (Or Lack Thereof)

Why is the C-S bond in $\ce{CH_2SH^-}$ longer than in $\ce{CH_3SH}$? Wouldn't there be resonance in the former, forcing the C-S bond to contract? ...
5
votes
1answer
181 views

Orbital overlap and size “mismatch”

Why is atomic size mismatch a sign of poor bond strength? Wouldn't orbital overlap be proportional whether the two atoms are small or the two atoms are big? For example I heard someone comment that ...
7
votes
1answer
716 views

Is cyclobutadiene anti-aromatic?

Cyclobutadiene is very unstable. But, some sources claim that this instability can be attributed to other factors such as ring and angle strain rather than antiaromaticity. Cyclobutadiene is simply ...
8
votes
1answer
190 views

Why F replaces axial bond in PCl₅?

Why does $\ce{F}$ replace an axial bond in $\ce{PCl5}$? I realize that it would be more stable there than at equatorial bond, but what is the reason of its stability? Similarly in $\ce{AB4}$ type of ...
0
votes
1answer
50 views

Conical intersections - phase

Can anyone explain why at a conical intersection the wavefunction changes sign? My understanding is that it is a test to see if the crossing IS indeed a conical intersection or just a coincidence of ...
6
votes
2answers
538 views

How does a Frost diagram reproduce the solutions to the wave equation?

I came across a Frost diagram for cyclic compounds in my book, and all my book had to offer was that it geometrically reproduces the solutions of the wave equation, and can therefore determine the ...
7
votes
3answers
374 views

Is the transformation of pi bonds to sigma bonds always energetically favorable?

Is the move from pi bonds to sigma bonds always favorable? My professor claims so, except in the case of conjugated pi bonds. I can see how pi bonds going to sigma bonds might be favorable; I know ...
15
votes
2answers
754 views

How many molecules does it take to have a phase?

A single molecule can't be solid, liquid or gas. It's just a molecule. A mole of something can be any of the three. So, how many molecules does it take for phases to be meaningful? I realize that ...