Unanswered Questions
8,738 questions with no upvoted or accepted answers
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Melting and boiling point trend in Group II
The following picture shows the melting and boiling point trends down group II elements.
I have added question marks where the variability in data was rather disturbing (over two hundred degrees ...
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How to calculate transition dipole moment from two known wavefunctions
I'm interested in calculating the transition dipole moment (TDM) from the information from two wavefunctions of different states. This is somewhat similar to calculating the molecular dipole moment ...
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Do Cyclohexane-1,3-diones Give Positive Haloform Reactions?
Recently a post appeared on ChemSE asking why cyclohexane-1,3-dione (dihydroresorcinol) 1a doesn’t give a positive iodoform test. Unfortunately, the post was subsequently taken down after several ...
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What is d-orbital collapse?
When I was perusing the works of Schwarz on atomic structure, I came across the unfamiliar term of d-orbital collapse.
He describes it as a variation in energetic sequence from group 1 to 3 elements ...
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Manuals for a Cahn TG-171 Thermogravimetric Analyzer
Recently a Cahn TG-171 Thermogravimetric Analyzer was donated to my school. We did not get a service or user's manual with it, and some of it still needs to be put back together.
I have tried to ...
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Tetrahedrane Properties and Analogs
I took a look into some tetrahedrane ($\ce{C4H4}$) analogs, platonic hydrocarbon, basically very strained tetrahedral geometry at every carbon. I was wondering what will be the predicted delta H of ...
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Rotation around CC bond in 1,2-dioxetane: transition states and local minimum structures
TLDR:
What: Potential energy surface associated with rotation around CC bond in the ring-opened version of 1,2-dioxetane.
How: State average(4)-CASSCF(12,10)/VTZP constrained geometry optimizations ...
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What is the largest coupled cluster calculation that has ever been done (as of March 2019)?
I am doing some research and trying to make sure the numbers I am reporting are accurate.
I found that the paper by Sylvetsky et. al. says:[1]
We were, however, able to complete a ...
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Inter electronic repulsion in s and d orbitals
This was written in a lecture slide:
Two electrons present in the same d-orbital repel each other more strongly than do two electrons in the same s-orbital.
Why is there a difference in the amount ...
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MNDO integrals in the global coordinate system
In MNDO and its descendants (Sewart's PMx models, Austin's AM1, MNDO/d, etc.), the nonvanishing two-center two-electron "coulomb integrals" are evaluated via a classical multipole expansion in a local ...
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What explains the color in clear sigma versus green pi complexes formed by methylbenzene?
Peter Sykes mentions in Guidebook to Mechanism in Organic Chemistry (6th ed.) on p.132 that there would significant differences in physical properties of the resultant mixture when we:
React ...
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Why do alpha-hydroxy ketones respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests?
I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests.
However, in another textbook I read that even alpha-...
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Rationalising diastereoselectivity of hydroboration using stereoelectronics
Using bulky reagents such as 9-BBN, hydroboration is often highly diastereoselective, giving rise to the 1,2-anti diastereomer:
This is easily explained using a steric argument, with the major ...
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Calculating Triplet-Triplet Spin-Orbit Coupling
According to the Q-Chem manual [1], the singlet-triplet spin-orbit couplings between a singlet excited state $I$ and a triplet excited state state $J$ is:
$$\langle\Phi_\text{singlet}^I|\hat{\mathrm H}...
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Accuracy of quantum chemistry calculations on iodine neglecting relativistic effects
Triiodothyronine is a molecule with three iodine atoms. If we attempted to calculate its properties with ab initio methods like Hartree-Fock or more complicated ab initio methods which included ...
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Is gallium slippery at room temperature in an inert atmosphere?
Ice is slippery when it isn't too far below it's melting point because the surface molecules are less loosely bound than the bulk and form a thin liquid layer.
Pressure melting is a much smaller ...
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Role of pH in azo C-coupling reaction, continued
In the question, "What is the role of pH in azo coupling reaction of diazonium with phenol and aniline?" asked by @DhrubaBanerjee and answered by @Klaus-DieterWarzecha, I find several ends ...
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Understanding two-electron integrals in Gaussian 09
I was comparing the two-electron integrals (electron repulsion integrals, ERI) printed by various well-established packages (Gaussian, GAMESS, Molpro etc.) and observed that Gaussian is the oddball in ...
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What is this golden looking substance?
I am currently messing around with gallium compromising aluminum. I am using a titalium lock which is just a brand of aluminum padlock and I put a gallium-indium euctic alloy on the surface of it. It’...
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Is there a structured data source containing information on the World Health Organisation's Stability Testing Policies?
Hoping to automate some product testing guidance software, I've been attempting to find a (hopefully live, up-to-date) Database, Web-service, or other structured data source containing the ...
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Color of methoxy substituted phenyl rings when heated in the presence of acid
Anyone who's familiar with organic synthesis will probably have came across the DMB and PMB protecting groups.
When TLC-ing compounds containing these protecting groups using common stains like ...
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Density Functional Theory with Generalized Gradient Approxmations (GGA) - What Happens if the Electron Density Shows a "Kink" at the Ion Position?
My question may be stupid, so please correct me if you find anything which is obviously erroneous.
In the following I will place a question mark (?) besides points/steps I consider doubtful.
My ...
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Doubt in Zeeman effect for sodium spectrum
I am reading an atomic molecular physics book (for Indian universities). You may not familiar with it. But you can download it from the link if you wish.
So in the book it is mentioned that for normal ...
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Using symmetry and group theory arguments to explain iron(II) in a tetrahedral crystal field
I am trying to figure out how to explain $1s \rightarrow 3d$ spectroscopic transitions for $\ce{Fe^{2+}}$ in $T_\mathrm{d}$ symmetry. These transitions make up the pre-edge region in K edge X-ray ...
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Frontier orbital analysis of zinc-catalysed carbonyl-ene reaction
Q1. Is the $\sigma_\ce{C-H}$ bond a donor in this reaction? If not, then can we take the alternate combination (HOMO of alkene, LUMO of the $\ce{C-H}$ bond and, HOMO of the carbonyl)?
Q2. We can also ...
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Why are IUPAC's definitions of exo- and endothermic disconnected from the direction of heat flow?
I'm wondering if anyone can provide a rationale for IUPAC's definitions of exothermic and endothermic since they disconnect these terms from the direction of heat flow.
Specifically, here are IUPAC's ...
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Does the alpha effect apply to third row elements?
Alkylperoxy anions are stronger nucleophiles than alkoxides (the so-called alpha effect), but would an alkyldisulfide anion be a better nucleophile than an alkylthiolate anion?
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Why is the bond angle of N-N-N in hydrogen azide not 180 degrees?
Chen and Wang (2009) have reported an $\ce {N-N-N}$ bond angle in the hydrazoic acid molecule of $171.5$ degrees using B3LYP/6-311G** model. The wikipedia page for the molecule also reports a similar ...
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In a molecular dynamics context, is the methyl rotation in propene a symmetric or asymmetric internal rotor?
In a prior question, I asked about the (a)symmetry of the potential energy surface of the methyl rotation of propene. In that context, the kinetic energy of the nuclear motions is of course assumed ...
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Which potentials are suitable for molecular dynamics simulation of simple explicit solvents?
Which potentials (force fields) are suitable for adequately simulating (mixtures of) explicit solvents? Interesting rheological properties include viscosity, surface tension, heat capacity.
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Why does the reaction of sodium nitrate, aluminium, and sodium hydroxide yield ammonia?
From Russian test problem 4301:
$$\ce{3NaNO3 + 8Al + 5NaOH + 18H2O -> 8Na[Al(OH)4] + 3NH3(g)}$$
How does ammonia evolve here? Is it that we get hydrogen gas evolving in the reaction between Al and ...
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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 ...
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Identifying alkyl ligands as π-donors or π-acceptors in transition metal complexes
Is there a systematic way to identify an alkyl ligand as a π-acceptor or π-donor in a transition metal complex?
Although various sources indicate that the weak field ligands are typically π-donors and ...
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Why are vapours of xenon hexafluoride coloured?
According to Wikipedia,
[...] It is a colorless solid that readily sublimes into intensely yellow vapors.
It is clear from the above statement that $\ce{XeF6}$ is colourless in solid form. But why ...
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Why does 1,4-diiodobenzene have a non-zero dipole moment?
From this answer, I came to know that 1,4-diiodobenzene has a dipole moment of $0.19~\rm D$ in benzene at $20\ ^\circ\rm C$. On the basis of symmetry, I'd expect the bond moments due to the difference ...
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Is there a reliable chemical theory that predicts pKa based on structure?
Obviously, there are general stability arguments that can be made to estimate relative pKas, such as evaluating the stability of the conjugate base of an acid, or thinking about how polarized the bond ...
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Can I make a mirror on PET plastic using Tollen's reaction?
I want to make a very shiny surface, like a mirror. I tried to use chrome paint but it's barely shiny. It's more like gray even though I bought one of the most expensive chrome looking paint.
I know ...
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Quantitative Transfer of Volatile Standards
(Edited w/ updates) Okay, long story short I work in a lab which has been working on cannabinoid analysis (in the licensed Canadian market) and have had a lot of issues surrounding the standards/...
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The Action of Nitrogen Iodide on Methyl Ketones
I recently encountered two old publications on action of nitrogen iodide on various compounds (Ref.1 and Ref.2). Between them, Ref.1 described the iodoform formation by methyl ketones upon treatment ...
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Vanishing integral rule for two-electron integrals
I understand the vanishing integral rule for a one-electron integral to be:
$$\langle i | \hat{O} | j \rangle = 0 \hspace{1cm} \mathrm{if} \hspace{0.2cm} \Gamma_O \neq \Gamma_i \otimes \Gamma_j$$
...
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Cobalt Chloride in various solvent/water mixtures - tested
In a recent post the solvatochromic behaviour of cobalt chloride in acetone was discussed. There were some ideas how the acetone might influence the ratio between the blue $\ce{[CoCl4]^2-}$ and the ...
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Quenching rates in nucleation MD simulations
I am trying to perform nucleation simulations with molecular dynamics. To prepare the metastable fluid, I am equilibrating at temperatures about 30 K above the melting temperature, and then "quenching"...
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Free Web-Based Orbital Solver to look into the Walsh orbitals of a perturbed cyclopropane
There exists a free online orbital calculator.
When I draw cyclopropane it plots three molecular orbitals, but unfortunately it doesn't use the Walsh orbitals.
Are there any free online tools which ...
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How to get defect-energy level diagram from PL data
I am reading this article Phys. Chem. Chem. Phys. , 2011, 13, 14902-14905 and seen that the authors have drawn a image of defect level using PL data
Can you explain me how this diagram can be drawn ...
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multielectron spin-orbit coupling and energy level
For multi-electron atoms for which the Hamiltonian (including the spin-orbit coupling) reads
$$H=\sum_i T_i-Z\sum_i V_i+\sum_i V_i^{\text{s.o.}}+\sum_{i>j}V_{ij}$$
The $T_i$ are the kinetic ...
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The Krieger-Li-Iafrate Approximation
I am having trouble understanding what KLI approximation is. Could someone explain it to me in an intuitive/simple way?
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Will the sulfur-iodine cycle and Haber Method work at lower pressures and temperatures?
I have a year-long research project next year in my senior year of high school, in which we have to make some product or prototype to solve some issue.
My interest was in the Liquid Fluoride ...
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Order of Basicity of Nitrogen Trihalides
I was asked to arrange nitrogen tri-halides in order of increasing basicity. On looking up the answer online, it turned out to be the following: $\ce{NF3}$ < $\ce{NCl3}$ < $\ce{NBr3}$ < $\ce{...
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Mysterious violet-purple compound in "Gerber Method" & "Banana oil synthesis"
During the determination of fat in milk (Gerber method), in a milk butyrometer are mixed milk + $\ce{H2SO4}$ 90% w/w + isoamyl alcohol (isopentyl alcohol) and heating.
The acidic mixture separates ...
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Why is octaoxygen diamagnetic?
I tried considering that according to LCAO-MO theory $\ce{O2}$ is paramagnetic, which is confirmed by experimental evidence. Since octaoxygen has the crystal structure in figure, I thought there is a ...
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