The Periodic Table

3:48 AM

@orthocresol Yeah sir... I'm sorry I said anion. Thank you very much for help.

4:17 AM

@orthocresol just one last question please... What would happen if the empty p orbital of the cation aligned with the sp2 sigma C–H bond of the 2nd carbon instead of the pi bonds and the empty p orbital? I mean why isn't hyperconjugation favored over resonance? Is that just a matter of priority? Thank you sir.

1,3-feeds

Q: 2019: a year in moderation

It's New Year's Day in Stack Exchange land... A distinguishing characteristic of these sites is how they are moderated: We designed the Stack Exchange network engine to be mostly self-regulating, in that we amortize the overall moderation cost of the system across thousands of teeny-tiny sli...

5 hours later…

Q: NMR magnetically equivalent protons for a 1,4-disubstituted benzene ring

9:08 AM

@OmegaKrypton You got it;)

@orthocresol Adding to Omega's explanation: t' is a time-reversing translation, the best symbol I could come up with for time travel; HNY is Happy New Year.

2 hours later…

Hot nitric acid (HNQ)

11:19 AM

Below I have drawn a molecule with random substituents $\ce{X}$ and $\ce{Y}$: If the distances from $\ce{H_b}$ and $\ce{H_a}$ to $\ce{H_d}$ are considered, they are different - $\ce{H_b}$ is 5 bonds away and $\ce{H_a}$ is 3 bonds away, so $\ce{H_b}$ sees $\ce{H_d}$ differently compared to $\ce...

organic-chemistry nmr-spectroscopy

1 hour later…

12:38 PM

I wonder what these socks are made of:

12:53 PM

@andselisk hello Happy new year :-)

@user8718165 Yaay, HNY:)

@andselisk yeah. How are you? BTW! This chat is really awesome :-)

@user8718165 Sober and happy that it finally snowed (one can tell I rarely drive a car) ). How are you?

@andselisk Wow! That's great :) I love snow. I'm fine too.

@andselisk I was just left wondering why t' indicated reverse time. :)

1:09 PM

@orthocresol Hii Ortho sir, could you please have a look at my question? Please :)

@user8718165 Yes. I am typing a reply. And don't call me sir.

That would be higher in energy than the alternative. It turns out that stabilisation derived from resonance is often far more effective than stabilisation derived from hyperconjugation. The molecule doesn't know what resonance or hyperconjugation is,
but it always wants to get to the lowest-energy configuration: this means having the pi orbital parallel to the empty p orbital.

@orthocresol Okay. I'm sorry. I'll just call you Ortho :-) And wishing you a very happy new year 😊

Happy New Year!

@orthocresol thank you so much :)

@orthocresol Is that because the sigma bond is more stable than the pi bond?

Hmm...

1:17 PM

@orthocresol okay... I was wondering why is resonance better than hyp. conj.? Does my reason make sense? I'm sorry if that's wrong.

I wish this chat had a way to show when people are typing. :)

It's a difficult question to answer and I think this will make more sense if you study MO theory in more detail.

Ultimately, though, it comes down to two factors: (1) orbital energies (2) overlap. The higher the energy of the filled orbital, the greater the stabilisation (generally). And the stronger the overlap, the greater the stabilisation.

@orthocresol yeah. I studied just basic MO theory, is is a deeper concept?

@orthocresol yeah, like whatsapp... But there's none :(

I was thinking more of something along these lines: chemistry.stackexchange.com/q/52158/16683 That would mathematically illustrate how the two factors above affect the degree of stabilisation, but won't make much sense if you don't do QM.

Anyway, usually the orbitals involved in resonance win in both aspects. For example, the C=C pi orbital is higher in energy than the C–H sigma orbital.

@orthocresol I'm so sorry. I know almost nothing about QM. Just learnt a bit about photons, HUP etc :(

@orthocresol yeah... fully got the 1st point... :-)

@orthocresol is there a similar argument for overlap? I'm not able to figure it out. Doesn't pi bond involve weaker overlap than the sigma?

1:36 PM

@user8718165 Yes, but it's not that overlap that matters. It's the overlap between the filled orbital & the empty orbital.

@orthocresol okay. Could you please explain it a little bit? I'll get it.

The pi bond is formed from two p orbitals. When you say the pi bond features weaker overlap, what you are really saying is that the overlap between those two original p orbitals is (relatively) weak. The overlap is thus not so much a property of the pi bond, but rather a property of the two interacting p-orbitals.

Likewise, the sigma bond does indeed feature stronger overlap, but that refers to the overlap between the constituent orbitals: a s orbital on H and an sp3 orbital on C.

@orthocresol Got it. Thank you so much Ortho :-)

@orthocresol You explained it in so much detail. Nobody explained it this way. Awesome

@orthocresol Enjoy the holidays. See you later 🎉😊