The Periodic Table - 2016-10-24 (page 2 of 3)

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2:00 PM

the thing about resonance is that you basically have an infinite number of resonance forms

user228700

Oh, never mind the formal charge...

user228700

Okay..? So, how do I continue from this?

in fact your resonance structure might be better (contribute more to the hybrid) than mine

just draw as many as possible

user228700

Yeah, but how to proceed from this? What can I shift..?

user228700

@DHMO Why do u say this?

2:01 PM

@Kaumudi there are several criteria for determining which structure contributes more

user228700

Oh, yeah, Ik. I have to look it up again.

@Kaumudi from the first structure, shift the double bond to the right hand side

user228700

Never mind that just now, then. Can u pls tell me how to proceed from the third structure?

I don't think you can

there is no rule saying that you must form a resonance loop lol

user228700

Yeah, that's exactly the problem :/

user228700

2:03 PM

:-P Ik, but...

user228700

Okay, how about this:

user228700

user image

@Kaumudi correct

user228700

Yeah :/ Now what? Just one moment...

user228700

Dude, u gotta forgive me for being so dumb, but I still do not get ur set of structures >.<

2:09 PM

@Kaumudi nobody said my set is perfect

i think your set is better

user228700

No, I don't get how u got them. Trying again...

why bother getting my set if your set is better?

I just shifted the double bond around the ring

user228700

Yeah, OK...

user228700

I'll still try tho, don't mind that.

alright

user228700

2:13 PM

Hang on, are u usually here at this time everyday? (Judging from this past week, I'm inclined to think "Yes"...)

@Kaumudi may be

user228700

OK...

user228700

Hey, fourth structure...

@Kaumudi ?

user228700

Why did u break the pi bond and give that other carbon a negative charge? Sulphur can expand its octet, right?

2:18 PM

@Kaumudi I did not account for the expanded octet.

user228700

(Oh God, "break"="real". Wtf autocorrect)

user228700

@DHMO Ah, so there can be a case where it's double bonded to both?

@Kaumudi I already said that your structure is better than mine

and yes

user228700

@DHMO Idc! I'm just trying to understand urs...

user228700

@DHMO Cool. Maybe I'll try that too. Anyway, point is that none of the lone pairs are delocalized throughout the compound (loop not completing), yeah?

2:21 PM

@Kaumudi you can say so

user228700

So, in cases like these, I consider all the lone pairs on all the atoms for calculation of steric number, yeah? (As opposed to say, furan or something; one of the lone pairs on oxygen in furan is definitely delocalized throughout the whole compound)

user228700

..?

@Kaumudi When trying to determine if something is aromatic or not you should never have to resort to expanded octets.

user228700

@orthocresol Oh, really?

Yes.

user228700

2:25 PM

Why not?

@orthocresol even in her syllabus?

@Kaumudi some lone pairs are indeed delocalized...

user228700

@DHMO Dude, why do u keep thinking I'm a guy?

@Kaumudi The moment you have two double bonds next to each other, you know you cannot use the same p orbital on sulfur for both, right?

@Kaumudi sorry

user228700

@orthocresol Well, yeah...

2:26 PM

What happens if we abuse in a chat

@Vedant @orthocresol will delete your messages

user228700

@Vedant Flags! Bans!

or even worse in an answer

For example, you'd have to use the $\mathrm{p_x}$ orbital for one double bond and the $\mathrm{p_y}$ orbital for the other. Just like in an allene.

/question

user228700

2:27 PM

@orthocresol Yeah...

user228700

So..?

@Vedant It'll be deleted, you'll get a warning. In chat, you'll probably get timed out for a period of time.

@orthocresol @orthocresol Mathjax doesnt work here right??

@Vedant gist.githubusercontent.com/berquist/…

Copy this text into a new bookmark and use it when you want to turn it on.

Alternatively, there should be a plugin, if you go to meta and search for "chatjax" you should be able to find it.

@Kaumudi What's your definition of aromaticity?

Does it involve "conjugated" somewhere?

@orthocresol Thanks, im watching ur txts like a idiot

not ableto comprehed Mathjax!!

user228700

2:30 PM

@orthocresol Yes...

Mmhmm. So, can a pi bond from a px orbital, and a pi bond from a py orbital be conjugated?

They're at 90 degrees to each other.

@Kaumudi That 5 membered ring you drew above? You know that's anti aromatic, right?

user228700

@Zhe Yeah, that's what is given in the answers. Was trying to figure out why...

user228700

@orthocresol Ohh, yeah...

@Kaumudi Each pi bond has 2 electrons.

Each heteroatom that isn't involved in a double bond has a lone pair in a p orbital, so 2 electrons.

user228700

2:32 PM

But only π bond is there, right?

2 + 2 + 2 + 2 = 8

Well, it depends on whether you assume it's going to be planar.

But for the purposes of this exercise, it seems like they want you to assume that it is all planar and everything is sp2 hybridised.

Thanks @orthocresol Love you! got mathjax workin .Now i understand something. how to impress mod

user228700

@orthocresol: OK, I was trying to figure out the hybridization of each atom in the ring to find out how many π electrons are there.

@Kaumudi Well, if you go back to furan, there's nothing stopping you from insisting that oxygen is sp3.

If furan's oxygen were to be sp3, the compound wouldn't be planar, and it wouldn't be aromatic.

user228700

But it looks like the carbons are all sp2 hybridized and the heteroatoms all look like they're sp3.

2:35 PM

It just turns out that "switching" to sp2 hybridisation is more stable, because that confers aromaticity.

user228700

@orthocresol Yeah, Ik, so one of the lone pairs is delocalized...

Here too, there is nothing stopping you from saying the sulfur and both nitrogens are sp3.

They very well might be.

user228700

Yeah...

It's just that if you assume that they are sp2, then you end up with an anti-aromatic 8 pi electron structure.

user228700

@orthocresol In furan, we assume its sp2 by having one lone pair be delocalized, right?

user228700

2:37 PM

How does it work here?

In furan, if you make oxygen sp2, then it will have three sp2 orbitals and one p orbital.

Two of the three sp2 orbitals are used for the O-C bonds.

user228700

And what's the point of assuming they're sp2 hybridized, but the molecule still being antiaromatic?

user228700

@orthocresol Yeah...

One more sp2 lone pair, and that leaves one p lone pair.

Which allows it to be delocalised.

Yeah, you got that.

As for what's the point, I don't know.

Actually, I do know

Since the planar molecule is antiaromatic, that probably means that it would prefer not to have the heteroatoms sp2 hybridised.

Which is why I don't think that that molecule is planar to begin with.

user228700

Yeah, so delocalizition, right? What about here? By drawing the resonance structures, I was trying to figure out if any of the electron pairs are delocalized, to make them sp2...

2:40 PM

@Kaumudi Ever looked at cyclooctatetraene?

1,3,5,7-

user228700

7

Q: Hybridization of the oxygen in furan?

I fail to understand why the hybridization of oxygen in furan is $\ce{sp^2}$. I think that since there are 2 bond pairs and two lone pairs so it should be $\ce{sp^3}$ hybridized? Is it to do with the aromaticity of furan? Please help

electronic-configuration orbitals hybridization

meh

user228700

..?

If you assume they're sp2, then you get anti-aromaticity.

Which isn't good for the molecule

user228700

Wait, it doesn't matter if my way is right or not. I just need a way to deal with this sp2/sp3 ambiguity when checking for aromaticity.

2:41 PM

@orthocresol what is anti-aromaticity?

So that tells you that your initial assumption is probably false.

@Kaumudi Aromaticity as a concept makes no sense if you have sp3 atoms peppered in between.

user228700

@DHMO 4n π electrons.

user228700

@orthocresol Yes...

To check for (anti)aromaticity you have to treat it as being planar first.

Planarity implies sp2.

user228700

Always?

2:42 PM

Yes.

For a cyclic molecule at least.

Then again, it's not like you're looking for acyclic aromatic compounds, so it doesn't matter.

user228700

So, hang on, I just assume they're sp2, whatever might be the case and then, I check Hückel's rule?

Yep

user228700

Wait, all the time?!

Yes.

And then, if you find that that gives rise to antiaromaticity, you know that in real life it probably isn't sp2.

user228700

I found all these guidelines that ask me to check for delocalization first and all, to then check...

2:45 PM

Oh, I see. Well, that's another possible way of doing it.

user228700

@orthocresol Ah, the dichotomy b/w "real life" and whatever Chemistry says "real life" is. So awesome.

user228700

@orthocresol Ah, OK! So, what about the diagram that I drew?

@Kaumudi No, no.

You know, in maths, something called proof by contradiction?

user228700

Ohh.

That's precisely what I'm describing.

user228700

2:46 PM

Okay...

To show that something isn't true, you assume it's true first. Then show that it's wrong.

user228700

Yeah, OK...

user228700

Wait, so what about my molecule?

Well, you could theoretically draw resonance forms for your compound.

Lemme do up a chemdraw sketch.

user228700

DHMO and I spent close to an hour drawing and discussing the possible structures!

user228700

2:47 PM

It's all there ^

user image

Did you get this one?

Too lazy to check.

@orthocresol can I move the double bond to the other direction to get the third one?

Yes, with the positive charge on sulfur

user228700

@orthocresol I didn't draw it, but I get how this works...

@orthocresol then why didn't your software draw it?

2:50 PM

@orthocresol Did you try throwing this into scifinder and seeing if it's actually been studied?

@Zhe Nah, not really bothered.

@DHMO I drew this manually.

@orthocresol ok, I see

user228700

@orthocresol: So OK, we drew cases in which these lone pairs get delocalized...

user228700

It didn't complete a loop.

Yup, precisely.

user228700

2:51 PM

But it still counts as being delocalized?

Well, if it can't go round the whole ring, then it's not fully delocalised.

You need a ring that has a complete pi system.

user228700

Yeah, that's what I thought too...

It's delocalised to a certain extent, but not quite enough.

user228700

So wait, can I or can I not count these lone pairs when calculating the steric number?

user228700

Even tho it's not fully delocalized...

2:53 PM

That's a difficult question to answer.

We have nothing to review. They're gonna fire me.

user228700

That would make every atom sp2 hybridized and then we're all happy and I can go have dinner :-P

You're asking how is it in real life, you mean?

user228700

No, I'm asking if I can count them as being sp2 hybridized. That would make it planar and conjugated but yeah, still not aromatic.

Which ones?

user228700

2:56 PM

It would make more intuitive sense than simply assuming that they're sp2 hybridized because we've found the molecule to be planar experimentally.

All of them?

user228700

The heteroatoms in particular.

@Kaumudi not aromatic is not the same thing as anti-aromatic

user228700

The carbons are already sp2 hybridized...

user228700

@Zhe Oh, yeah, sorry. It's anti-aromatic.

user228700

2:58 PM

At the end if the day, I just want for it to make sense.

user228700

And assuming that the heteroatoms are sp2 hybridized doesn't exactly make sense 'cause the electrons aren't fully delocalized. Still, it makes more sense than just assuming them to be sp2 hybridized for the sake of matching the experimental evidence of the molecule being planar.

@Kaumudi I'll be surprised if there's experimental evidence of the molecule being planar.

I'd be strongly inclined to think that it isn't.

user228700

Wait, what?

user228700

Ah, proof by contradiction.

Precisely. Planarity would imply anti-aromaticity, something that is quite unfavourable.

If you see cyclooctatetraene, as Zhe mentioned, you'll notice it bends to avoid being planar.

user228700

3:02 PM

Okay, so wait. Can u pls just tell me what to do in such cases? (Where heteroatoms seem to be sp3 hybridized)

Step 1: Assume everything is sp2, just for the sake of checking Huckel's rule.

Step 2: Count pi electrons. If it's 4n+2, fine, it's probably sp2.

user228700

@orthocresol Ohh. Anti-aromatic different from non-aromatic!!

user228700

OK..?

Step 3: If it's 4n, then something is probably not gonna be sp2.

user228700

'Cause it doesn't want to be anti-aromatic, OK...

3:03 PM

Mmhmm.

user228700

But what if I'm supposed to check for anti-aromaticity?

Well, I would be very careful with my wording here.

Then it's 4n.

And that's a different story altogether

Let's use cyclooctatetraene as a simpler example. I'll use "cot" as a short form for that.

The molecule will prolly distort their geometry.

3:04 PM

Real-life cot, which is non-planar, is not anti-aromatic, precisely because it distorted its geometry to avoid being anti-aromatic.

user228700

No, I meant that in that in that case, I can't just assume sp2, no?

user228700

@orthocresol OK...

The hypothetical planar molecule of cot is anti-aromatic.

@Kaumudi The only reason you assume it is to check Huckel's rule.

user228700

@orthocresol After us assuming everything is sp2?

If it's aromatic, then you accept your hypothesis.

user228700

3:05 PM

If not..?

user228700

(If anti-aromatic)

If it's not, you reject your hypothesis, and you write something like "If this compound were to be planar, it would be anti-aromatic".

user228700

@orthocresol So only if I know for sure, if the compound is planar or not can I say if it's anti-aromatic or not?

Strictly speaking, yes, you can only assign these labels if you know the molecule is planar.

user228700

Ahhhhh, OK!!

user228700

3:07 PM

All cleared up. I bow down to you, mighty seal!

user228700

Thanks so much! :-D

No problem.

BTW, I just want to make sure

@Kaumudi He's not that mighty

You can still do a hypothetical treatment of a hypothetically planar molecule.

So, even if X isn't planar in real life, on paper you can still discuss its hypothetical properties if it were to be hypothetically planar.

Which is probably the entire point of your exercise. Even though the compound you're given probably isn't planar, you can still talk about a theoretical planar form of it, which would be anti-aromatic.

He's prolly a meter long. That's 3.28084 feet for people that don't like nice numbers.

3:10 PM

@Kaumudi still don't understand, sorry

Antiaromaticity

Antiaromaticity is a characteristic of a cyclic molecule with a π electron system that has higher energy due to the presence of 4n electrons in it. Unlike aromatic compounds, which follow Hückel's rule ([4n+2] π electrons) and are highly stable, antiaromatic compounds are highly unstable and highly reactive. To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions. In contrast to the diamagnetic ring current present in aromatic compounds, antiaromatic compounds have a paramagnetic ring current, which can be observed...

Google is just a tab away.

what the hell is that rule...

never heard of it

Antiaromatic compounds would be higher in energy than normal.

(due to my ignorance)

No, due to your only paying attention to exam material

I heard that's called focus, not ignorance

3:14 PM

@M.A.R. if I only paid attention to exam material, I would not even study resonance

or molecular orbitals

@M.A.R. Can you flag this chemistry.stackexchange.com/questions/61506/… as a dupe of this chemistry.stackexchange.com/questions/50684/…

Can I flag that as a dupe of that?

i just want somebody to start the closing process

I prolly can.

its presence on the front page is triggering me

3:19 PM

@orthocresol Ben looks cool

yeah :P

i just saw that too

user228700

3:45 PM

@orthocresol Yes, I realize this. However, I was just making sure 'cause I'm pretty sure that the examiners don't want us to choose options that aren't anti-aromatic simply by assuming sp2 all over.

I see. Yeah, good idea.

user228700

@orthocresol What "hypothetical properties" are u talking about?

user228700

(BTW, I just realized this. I don't even have anti-aromatic molecules in syllabus :-P But it's great that Ik about them)

user228700

@M.A.R. :-)

Aromaticity or antiaromaticity or lack thereof.

user228700

3:47 PM

Okay...

user228700

Thanks, again :-)

user228700

@M.A.R. :-P Still is. He/She(?) is pretty rad for having taken the time to explain all that so clearly.

user228700

@DHMO Sorry, I didn't explain everything. Yeah, it would be best if u just Google it.

@Kaumudi never mind, I understand now

user228700

Cool :-)

user228700

3:50 PM

Okay, folks! I think I'm done doing Chemistry for the day. Night! (And THANKS! :-D)

user228700

4:11 PM

Oh, BTW!

user228700

We have molecules like these:

user228700

user image

user228700

(4)

user228700

It already looks like every atom is sp2 hybridized.

user228700

However, for aromaticity, we have to assume that the N is sp hybridized!

4:14 PM

Yes.

user228700

This is OK, right? I mean, does it being sp hybridized cause angular strain or something, which causes the molecule to not be planar? (This compound is aromatic!)

Yeah, it's OK.

user228700

No angular strain?

Even if there's additional angle or bond length strain, it's compensated for by the aromaticity.

user228700

OK...but sometimes, steric strains overweigh the stability caused by aromaticity, no?

4:16 PM

@Kaumudi Do you want me to give you a test question to check your understanding?

user228700

Yes, please!

Do you know what an oxirane is?

aka epoxide

user228700

God, I've forgotten...

Take a cyclopropane and replace one of the C's with an O

user228700

OK...

4:17 PM

That's ethylene oxide

anyway, that's also called an oxirane

user228700

OK...

user228700

U want me to check for aromaticity?

I once asked during lecture if a certain kind of oxirane chemistry also applies to _oxirene_s

Why was this a stupid question?

user228700

_oxirene_s?

emphasize taht this is different

ene insteaf of ane

user228700

4:20 PM

A "certain kind of chemistry"? Hm...

Don't worry about that part

user228700

Well, in case this "certain kind of Chemistry" is aromaticity...

Focus on the oxirene

(You'll probably want to draw it out)

user228700

Focus on it and what?

Draw it out maybe?

user228700

4:22 PM

Wait, what's ur question?

Why was asking about oxirene chemistry stupid on my part?

user228700

Oxirene looks like this, yeah:

user228700

user image

user228700

Nvm the 38 :-P

So, why was this a stupid question for me to have asked?

user228700

4:25 PM

What was the question?!

@Zhe who said that this was a stupid question?

I did!

I asked if certain types of oxirane chemistry applied to oxirenes.

And yes, it was not a good question

user228700

Oh!

user228700

Do u mean how oxirenes are waay more stable 'cause if aromaticity and how oxiranes and ixirenes probably don't have the same type of Chemistry?

You're on the right track, but you got the wrong answer :(

I have to go to lunch, but think about how aromaticity applies to this molecule

user228700

4:30 PM

:-(

user228700

Okay, I will...

user228700

Thank you.

@Kaumudi Count electrons!

user228700

4:54 PM

Oh, shit!

user228700

I didn't even bother!

user228700

Oxirene is anti-aromatic!

5:06 PM

That is correct. Even if oxirene chemistry is interesting. Making it is going to a real pain..

Anonymous

@Zhe Does it exist btw? I don't think it can

I don't know of any references to oxirenes being made

Which made it stupid to ask if you can do chemistry to it...

Anonymous

Me too :/ ...too much strain =)

The strain isn't the biggest problem...

Anonymous

and AA

5:15 PM

yeah :)

Anonymous

damn, at first i thought O could delocalize both lp but that was flawed logic :-P

Anonymous

only one lp can move around

Anonymous

@Zhe never seen you here on chat...where are you from ? which country?

I'm in Boston

Pretty new to chat

But I found my way in after a prolonged discussion in comments

Anonymous

welcome :-) have a good time

5:19 PM

Haven't been a chemist in many years, but I saw a link to chemistry.SE from SO

thanks!

user228700

5:29 PM

@Zhe Riight!

5:46 PM

@Zhe You know, you could just have come to chat and asked me how to come to chat.

Sheesh, these new users don't even do any basic research...

@M.A.R. Your meta post is boring

In fact this whole place is boring...

I've had enough of moderating this place, bye guys.

Seriously though, meta participation is pretty much zilch now.

Please go and post something there, even if it's just a simple "This makes sense, I agree" comment!

6:23 PM

@orthocresol YOUR FACE IS BORING

@orthocresol Well, what did you expect?

Told you it'd be like this after the election.

But you can enjoy the soothing feeling that when you see a quiet meta and stay there, you can officially count yourself in the core group of the site that help things run smoothly and don't fall apart.

@Kaumudi ORTHO'S A SHE. ORTHO'S A SHE!

I again missed @Zhe.

@M.A.R. We need another election. Now

@orthocresol finding chat was not hard. finding the right room was more challenging

I kept thinking, no, I don't want to discuss the periodic table right now

@Zhe You can safely blame LordStryker for that

6:40 PM

1

Q: What is the correct definition of Hydration Enthalpy and why is it always negative?

The first definition of hydration enthalpy I found on the net is : The hydration enthalpy is the enthalpy change when $1$ mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution. Hydration enthalpies are always negative. Another definition I found in a b...

physical-chemistry thermodynamics

6:56 PM

@M.A.R. Ugh, I commented on that question without seeing your comment...

Couldn't tell which part of the question was the actual homework part...

@Zhe Which question?

the redox one with Fe and Cl

Hmph.

The more the merrier

Hi everyone !

@Zhe Heh... Well, I have the power to rename this room.

Oct 3 at 11:17, by Loong

room topic changed to Периодическая система химических элементов: Haikus are awesome / Chemistry's even better / So pull up a chair [blowing-the-lab-up] [german-stuff] [hullo] [love-you-all] [martin] [table-flipping] [tre] [welcome]

7:08 PM

@orthocresol how do you do this king of message ?

@Zhe Doesn't really matter that much, you can help homework guys in comments or even answers if you want.

@9-BBN hover over a message, click the green arrow on the left

click on permalink

copy-paste the URL of the window that opens into chat

Green hum where ? ^^

user image

it's green for your own messages, brown for others' messages, it seems

2 mins ago, by orthocresol

@9-BBN hover over a message, click the green arrow on the left

:D

I thought it was tricky haha

But impossible is not French

Today I add an exam about organic chemistry in one of the exercise there were a step with a diene and a vinylthioether and they add they heat it... I don't know why but I failed here I forgot Diels-Alder :(

I suck lol

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