Unanswered Questions

8,622 questions with no upvoted or accepted answers
25 votes
0 answers
2k views

How to calculate transition dipole moment from two known wavefunctions

I am 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 ...
23 votes
0 answers
4k views

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 ...
20 votes
0 answers
1k views

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 ...
20 votes
0 answers
443 views

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 ...
16 votes
0 answers
386 views

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 ...
15 votes
0 answers
352 views

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 ...
14 votes
0 answers
397 views

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 ...
13 votes
0 answers
358 views

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 ...
13 votes
0 answers
382 views

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 ...
13 votes
1 answer
7k views

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-...
12 votes
0 answers
223 views

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 ...
12 votes
0 answers
262 views

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}...
12 votes
0 answers
302 views

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 ...
12 votes
2 answers
4k views

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 ...
11 votes
0 answers
1k views

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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