Ask Us Anything!

It is fantastic, that you finally created this thread, @5hyl33n! I wish you and of course @TypicalNerd the best and hope for success. Maybe I ask or even answer a question too.


What kinds of questions can be asked? questions about the curriculum? lessons? certain subjects in chemistry?

For metal organic frameworks used in water harvesting, how do the intial water seeds bind to the metal centres?

Hi!
I did a mock interview yesterday where I was asked quite a complex chemistry question that I didn't understand. I was given the rates and concentrations of reactants (rate equation and order of equation style question). I was meant to determine that hydroxide ions have a 0 order. However, I was then later on meant to deduce a mechanism of nucleophilic substitution with hydroxide ions of a haloalkane knowing that hydroxide ions are 0 order. How would the mechanism change if hydroxide ions are 0 order? Sorry if this is quite a weird question

Just about anything chemistry related could be asked if you so wish. The only real restriction I would impose is that we can't do assignments or homework for anyone on this thread as that defeats the purpose of teachers/lecturers/tutors etc setting it.

That is an interesting question and I am not entirely sure I can give a definite answer as I haven't studied MOF's (metal organic frameworks). What I can do, however, is attempt to make a guess as to what happens having spent 5 minutes googling MOF's and some of the research on them.

My understanding is that the structure of the MOF results in there being several pores in which water molecules are able to fit, though the extent of hydrophilicity depends on several factors such as surface area, the valency of the metal ion(s) present, how exposed the metal centres are for binding and the relative sizes of the pores.

My guess is that since the extent to which the metal centres are exposed is a factor in the hydrophilicity, the formation of dative covalent bonds between the oxygens of the water molecules and the metal centres could be one possible explanation. However, the mechanism by which the initial water seeds would bind to the MOF could depend on what substance is used and what the coordination of the metal present is like. If the metal is heavily coordinated, then it is improbable that there will be any dative covalent bonding between the initial water seeds and the metal centres as there will be insufficient space to fit water molecules around the metal centres and instead it could be argued that the water molecules in the initial seed would instead experience hydrogen bonding with functional groups in the ligands.

Given you are likely better versed in this area, if you have any alternative explanations, I would love to hear them.

Thank you so much.

It's been a struggle trying to find an answer to this, as most papers on the topic don't mention this at all. The closest I've got to was a mention of ligand formation with Cu2+ and water molecules. Are metal centres the same as transition metal complexes but with organic linkers and in this case, water seeds instead?
Also, I remember reading the effect of the organic linker's polarity affecting the ability of MOF to release water molecules as vapor. Was wondering if you'd know much about this?

Okay, so here is my first chemistry related question: in this thread it were mentioned the id-id and pd-pd states of Van der Waals forces. Just to make it clear for myself: are these certain states of orbitals electron get when they are changing their positions?

@5hyl33n of course, you are requested to anwer to the question too!

Thank you again! I was also wondering if you happened to know the mechanism for amide link formation (something that an A level student would be able to understand) ?
I asked my chemistry teacher today about why HOOC-R-NH3+ doesn't form amide links in a test tube, and he said that we need an enzyme in order for it to happen. So I'm not sure what to reply with to the interview question, without considering the mechanism. I'll try and write up a reply to the dms tomorrow if time allows it! Really appreciate the help 🙂

Hello! Quick (if you can call it quick) question:
I have read 6 papers trying to understand the following mechanism for the formation of a triazole using Cu(I) as a catalyst.
Would you please be able to explain what happens at number 2 and 4 (link attached)?
From number 2:
From number 4:
I have studied some ligand-based reactions but not many, so thank you so much in advance!

https://ibb.co/4FcjFvy

Ah this reaction was I believe the subject of last year's nobel prize and I studied it briefly before this year's olympiad round 1, so as to understand the kinetics behind it as I (incorrectly) predicted it would be a topic that came up. Though the mechanism I was familiar with was rather different from the one you have linked: https://www.organic-chemistry.org/namedreactions/click-chemistry.shtm

The first copper(I) attaches to the alkyne through a dative bond, because terminal alkyne protons are somewhat acidic (pKa ≈ 25) and certain bases can remove them, which leaves an available lone pair. Once you get to undergraduate level, you will come across hybridisation theory and you will learn that the carbons in an alkyne have sp hybrid orbitals, which are of relatively low energy (as they have 50% s-orbital character and you will also study radial distribution functions which can be used to justify the fact that orbitals with high s-orbital character tend to be closer to the nucleus and of relatively low energy) and so the lone pair within would be relatively stable, which allows for the terminal alkyne to deprotonate to a reasonably stable conjugate base.

I am not entirely sure as I haven't looked into homometallic bonding in much depth. I would think that what happens does involve available orbitals (in the fourth quantum shell) in the copper(I) ions allowing for the formation of a homometallic bond. However, since the explanation of the mechanism I am more familiar with states that the second copper (which would be the one that replaces the hydrogen at the terminal alkyne position as per the mechanism as I knew it) is a stabilising donor ligand after the formation of the 6-membered metallocycle, it is possible you could be (mostly) right.

You can get bonding electrons moving to form new bonds in both covalent and dative covalent bonds. There aren't many examples of the electron pair in a dative bond being used in this way that I am aware of, but I'm sure that if you decide on studying chemistry at undergrad level, you will come across a number of mechanisms in which covalent bonds react in this way (hydride shifts and carbocation rearrangements spring to mind).

Hi, sorry for all the questions!
So for conjugated molecules, that exhibit colours -such as chromophores- within the visible light region. How does the resonance structure affect which photon is released, and how does the structure change when absorbing EM radiation vs releasing photons?

Hello @TypicalNerd , you asked on another thread which college my son had an interview for. It is Wadham. He’s getting a bit anxious particularly as we don’t have the touch screen tech they’re asking for. He’s waiting for school to see if they can provide an IPad and stylus.

He’s also a bit worried as there are topics school haven’t covered yet, particularly in Organic Chemistry. He’s read ahead a bit but would find answering questions on any of these topics difficult. Is it ok to say you haven’t covered something or do they expect you to give it a go anyway?