[Loz17]

(Original post by EierVonSatan)
What?

The more CO₂ that dissolves, the more carbonic acid there is. Therefore you get more H⁺ and so you end up with a lower pH since pH = - log [H⁺].

So pH decreases with increasing acidity.

So it's just my A level teacher's fault/some confusion along the way then. That's good news I guess

Thanks.

Warning guys I might have another question later

[cllio]

I dislike the photo for this society... for the obvious reasons. just saying

[illusionz]

Quick Q not deserving of its own thread:

Can you cleave methyl enol ethers with HBr in the same way you can cleave normal methyl ethers? I can't see why not but these things sometimes don't always work for similar groups. Tried a google search and nothing, lecture notes don't mention it.

[ste_mc_efc]

does anybody know of any good online revision resources? for undergraduate level physical/inorganic chemistry? 1st and 2nd year preferably.

[Loz17]

I still cannot get my head around mechanisms. I have an exam on it in about a month (but 6 others before that) and I'm ****ting it as it's worth 70% of the module. I have a high 2.1 fir the coursework but I doubt it's going to help all that much

[illusionz]

(Original post by Loz17)
I still cannot get my head around mechanisms. I have an exam on it in about a month (but 6 others before that) and I'm ****ting it as it's worth 70% of the module. I have a high 2.1 fir the coursework but I doubt it's going to help all that much

What about them don't you understand?

[Loz17]

(Original post by illusionz)
What about them don't you understand?

I can never really picture the correct movement of electrons; where they move from first and where they move to to form what I need, as well as which resonance structure to use when needed, which bonds are intermediate bonds in transition states and where other reagents attack.

I basically just need to learn o.chem from basics again but time issues worry me

[illusionz]

(Original post by Loz17)
I can never really picture the correct movement of electrons; where they move from first and where they move to to form what I need, as well as which resonance structure to use when needed, which bonds are intermediate bonds in transition states and where other reagents attack.

I basically just need to learn o.chem from basics again but time issues worry me

Do you know about/understand HOMOs and LUMOs?

[Loz17]

(Original post by illusionz)
Do you know about/understand HOMOs and LUMOs?

Yes I do. Is that a massive key to mechanisms?

[illusionz]

(Original post by Loz17)
Yes I do. Is that a massive key to mechanisms?

Massive doesn't quite do it justice. Go find any mechanism in your textbook. The arrows will show electrons moving from the HOMO of one species to the LUMO of another. If you know the HOMO and LUMO of two molecules then you can work out what will happen.

For example, take simple bromination of an alkene.

The alkene has HOMO being the pi bond and LUMO the pi*.
Bromine has HOMO being the lone pair and LUMO being the sigma*.

If you tried to pair up the HOMO of bromine and the LUMO of the alkene you'd end up drawing some arrows which would look rather silly - simple alkenes are not electrophilic. However, if you pair up the HOMO of the alkene with the LUMO of bromine you get your reaction. The highest energy electrons of the nucleophile attack the lowest empty orbital on the electrophile, which being the sigma*, breaks the Br-Br bond giving you your reaction mechanism.

I can talk you through other examples too if you want.

I haven't come across a reaction in organic chemistry yet that can't be explained with HOMO/LUMO interactions.

[EierVonSatan]

I barely use HOMO/LUMO thinking in mechanisms Each to their own

[illusionz]

(Original post by EierVonSatan)
I barely use HOMO/LUMO thinking in mechanisms Each to their own

I only use it when confronted with something I haven't seen before, but I reckon it's pretty fundamental when it comes to understanding what is actually going on.

A huge amount of the stuff we've done this year has required us to think about the actual orbitals involved. Be it ring formations with Baldwin's rules, pericyclics, stereochemical issues, hard/soft nucleophiles/electrophiles and more. The orbitals involved are the HOMO and the LUMO so I end up thinking about them all the time

[Loz17]

(Original post by illusionz)
Massive doesn't quite do it justice. Go find any mechanism in your textbook. The arrows will show electrons moving from the HOMO of one species to the LUMO of another. If you know the HOMO and LUMO of two molecules then you can work out what will happen.

For example, take simple bromination of an alkene.

The alkene has HOMO being the pi bond and LUMO the pi*.
Bromine has HOMO being the lone pair and LUMO being the sigma*.

If you tried to pair up the HOMO of bromine and the LUMO of the alkene you'd end up drawing some arrows which would look rather silly - simple alkenes are not electrophilic. However, if you pair up the HOMO of the alkene with the LUMO of bromine you get your reaction. The highest energy electrons of the nucleophile attack the lowest empty orbital on the electrophile, which being the sigma*, breaks the Br-Br bond giving you your reaction mechanism.

I can talk you through other examples too if you want.

I haven't come across a reaction in organic chemistry yet that can't be explained with HOMO/LUMO interactions.

That makes a lot of sense. I'll probably look back over HOMO/LUMO interactions tonight then apply these ideas to some mechanisms. I'll let you know if I need another example. Thank you!

[cpchem]

(Original post by EierVonSatan)
I barely use HOMO/LUMO thinking in mechanisms Each to their own

Ditto. But then I'm a dirty transition metal chemist, so what do I know?

[Kallisto]

I have questions for interest.

While an acid transferred a proton to a reactant and evolves an oxonium ion (H3O+), a base evolves hydronium ions (OH-) (in an aqueous solution of course). Is that the reason why an acid and a base are neutralized in an aqueous solution, because the kation (H3O+) and anion (OH-) will be neutralized after such a chemical reaction?

Is it possible that kation and anion react to water? That makes sense in my mind, because
acid and base react to water and salt, if both of them are reactants.

That would be my chemical equation: H3O+ + OH- -> 2 H2O.
Hydrogen would be the proton which is transferred.

Is that all right?

[danhirons]

[Loz17]

I never thought I'd see the day that o.chem would completely baffle me, whereas I understand thermodynamics and spectroscopy (so the many works of Boltzmann) to a good extent

[EierVonSatan]

It turns on you in the end. At least phys chem warns you away, org chem pretends to be your friend but ends up taking you for a ride

[Loz17]

(Original post by EierVonSatan)
It turns on you in the end. At least phys chem warns you away, org chem pretends to be your friend but ends up taking you for a ride

I hope it because my friend in the next 2 days otherwise I'll be failing this module

[shengoc]

Hey fellow organic chemists, some help here please. Do you think that would work? I would need to lithiate the protio ligand in the end for salt metathesis reaction but i figure an aqueous work up stage might be useful to just confirm that I have made it or something.

Thanks. Any advice is appreciated.