The Periodic Table

getafix

12:52 PM

Hello!

Is there anyone out there..I need some help.

orthocresol

1:42 PM

@getafix What do you need help with/

That was supposed to be a question mark, but a forward slash works too.

getafix

can i upload like a picture here?

I had this question and we were supposed to identify the chiral centres, mark them R/S and identify an internal plane (if any) ..

I id'd two S centres..and one mirror plane..that I have indicated in the diagram..am I correct?

In general, I am having some trouble with the stereochemistry of such cyclic molecules..

Loong

2:00 PM

@getafix You only have one double bond. So the mirror plane in your drawing cannot be correct.

getafix

But if I reflect internally, won't the double bond shift to the other side, so its position relative to the other groups doesn't change? am i getting this wrong?

are the labels for the chiral centres correct though?

Loong

There actually is a mirror plane. It is parallel to the paper plane. So one of the chiral centres is the mirror image of the other chiral centre. So one centre has to be R and the other has to be S.

getafix

ah okay.

I see..

How does one generally go about identifying such planes?

Loong

2:16 PM

I don't know, whether there is a mathematical recipe that is generally applicable but still practicable. I look at the drawing, imagine the actual three-dimensional structure, and try out the possible reflections.

getafix

I see..are there any rules that i must follow while reflecting?

orthocresol

Hmm, for this molecule, as Loong pointed out there is only one double bond. So if there is to be a mirror plane, it must either contain the double bond or bisect it.

getafix

I see.

Loong

@getafix Make sure that you don't change anything else when reflecting the molecule.

orthocresol

I think with more practice you'll be able to develop some intuition

getafix

2:24 PM

i do laterally invert when i reflect right?

orthocresol

I just think of it as a mirror.

getafix

wait..so..

orthocresol

Sorry I'm not 100% sure about what you mean by the term laterally invert (havent seen it for a long time)

getafix

right becomes left, left becomes right

orthocresol

Yeah but right and left depends on which way you are looking at it.

getafix

2:28 PM

orthocresol

chemtube3d.com/ClaydenPlaneSymmetry.html

getafix

Again, a similar compound, only one stereocentre..is it an S? I am having trouble applying the CIP rules to such compounds.

orthocresol

Looks S to me

And the other bridgehead carbon is also chiral

getafix

but isn't it linked to 3 CH2 groups?

orthocresol

Yeah, but if you look beyond the CH2 groups, it differs.

getafix

2:32 PM

oh okay..

and would this be S or R?

orthocresol

here the hydrogen is "coming out"

getafix

Yeah, how can we tell? like the implicit hydrogens aren't labelled, and I have no idea which way they go..

orthocresol

Try and make a model of the compound if you have a set

getafix

Unfortunately, I don't. just pen and paper..

orthocresol

Well, you could think of the two C-C bonds to the side as being in the plane of the paper

then the C-C bond to the top has to go inwards, otherwise it's not going to reach the other side of the ring

getafix

2:40 PM

okay, that makes sense..

ahh

and the hydrogen has to point out..

orthocresol

and if the central C wants to have a tetrahedral geometry, or anything near it

yep the hydrogen has to point outwards

so same thing for the carbon behind

that hydrogen is pointing away from us

getafix

so this one should be an R?

because we rotate so that we can have the hydrogen pointing away from us

orthocresol

to me it seems to be an R

getafix

and the plane of the paper acts as an internal mirror for this one as well?

orthocresol

nah, there's no mirror plane here

it might help if you look at the original compound without the ketone first

Norbornane

Norbornane (also known as bicyclo[2.2.1]heptane) is an organic compound and a saturated hydrocarbon with chemical formula C7H12. It is a crystalline compound with melting point 88 °C. The carbon skeleton is derived from cyclohexane ring with a methylene bridge in the 1,4- position, and is a bridged bicyclic compound. The compound is a prototype of a class of strained bicyclic hydrocarbons. The compound was originally synthesized by reduction of norcamphor. The name norbornane is derived from bornane, which is 1,7,7-trimethylnorbornane, being a derivative of camphor (bornanone). The prefix nor refers...

there are 2 mirror planes in this molecule

getafix

2:44 PM

One across 4, 1?

orthocresol

one of them contains 2.5, 5.5 and 7 (where 2.5 is the midpoint of 2 and 3)

and the other one contains 1, 4, 7

getafix

I see.

orthocresol

now if you add the C=O group in, on carbon 2

getafix

the symmetry is disrupted..

orthocresol

neither of the mirror planes work anymore

yep

that molecule has lower symmetry

getafix

2:46 PM

can the plane of the paper acts as a mirror here?

orthocresol

nope

the C=O will be flipped over to the other side

getafix

aah okay..

stupid question..after reflection, does at have to match automatically or are we allowed to rotate it to make it fit?and check to see if it works..

orthocresol

Yeah i wanted to come to that actually.

And for this it's probably better to look at the first alkene above

the mirror plane that you drew in the diagram - if you reflect the molecule and then rotate by 180 degrees, it can be superimposed on itself

that only implies that the molecule isn't chiral overall (there are chiral centres but its not chiral - i.e. that alkene is a meso compound)

however, it doesnt mean that that plane is considered to be a plane of symmetry

for a plane to be a plane of symmetry, you can't do any more rotations on it

getafix

i see...

orthocresol

What level of chem are you studying?

getafix

2:52 PM

I am second year, undergraduate

first time taking ochem in uni.

orthocresol

Ah okay

If you have a course on molecular symmetry, i guess you will study these stuff in more detail, it usually comes under inorganic

getafix

I see. we won't have courses on that till next semester..

So, I guess the best way to work this out is do more exercises?

orthocresol

I guess so. That can be said of a lot of things, I think.

getafix

another stupid question: if a molecule has two chiral centres, one R and the other S..is it automatically a meso compound? I feel no..

orthocresol

i'll let you draw your own conclusion haha

getafix

3:01 PM

aah okay..so if it is RR or SS then it cannot be meso, but if it is R and S, and has an internal mirror plane then it is meso..otherwise..no??

inɒzɘmɒЯ.A.M

@orthocresol Hey that somehow occurs to me as those "kosher vs. non-kosher" posters.

orthocresol

@getafix These actually don't have a mirror plane, they have a centre of inversion. But I guess, you'll learn that next semester... Anyway, it's pretty complicated. There are formal rules for determining the chirality of a compound. But for the simple case here, where there are 2 chiral centres, it has to be (RS) and the groups attached to both chiral centres have to be the same.

inɒzɘmɒЯ.A.M

TRE stats

getafix

i see.

orthocresol

So the top-left compound isn't meso because it's (RR), and the bottom-left isn't because the LHS chiral centre has (H, CH3, OH, CHClCH3) and the RHS chiral centre has (H, CH3, Cl, CHOHCH3).

getafix

3:09 PM

okay..i see.

inɒzɘmɒЯ.A.M

@orthocresol While you're at it, could you gimme a nice online thingy to study about symmetry?

(Molecular symmetry)

orthocresol

@in Let me search. I learn these stuff from lectures and textbooks so not too sure about online resources

getafix

@inɒzɘmɒЯ.A.M What level of chem do you study, again? just curious.

inɒzɘmɒЯ.A.M

@getafix That's . . . hard to tell.

I study here and there, studying everything that I might in the university one day.

getafix

You aren't university yet? somehow i pegged you for an undergrad..lol

inɒzɘmɒЯ.A.M

3:15 PM

*need dammit.

@getafix I'm only 16.

getafix

oh wow. cool.

actually, that is quite impressive..

orthocresol

@inɒzɘmɒЯ.A.M This isn't bad reciprocalnet.org/edumodules/symmetry/intro.html if you can load the java stuff

inɒzɘmɒЯ.A.M

3:28 PM

\o @Mart the mod/Mod the Mart

Jan

6:15 PM

Right, the gauche-effect question has an answer!

0

A: How can the gauche-effect be explained?

The gauche effect is commonly explained with LCAO-based bond orbitals. LCAO is short for linear combination of atomic orbitals and implies that we can take two atomic orbitals $\phi_1, \phi_2$ and create two molecular orbitals $\psi_1, \psi_2$ from them by linear combination: $\psi_1 = a_1 \phi_1...

Awaiting @wild and all the other quantum chemists to flog me for bad word usage xD

Loong

6:37 PM

This is the best answer I have seen so far in chemistry stackexchange. — Aditya Dev 3 mins ago

Wildcat

Meow! :D

The gauche effect, as a special form of hyperconjugation

Oh, boy! :)

Jan

It's probably because Aditya just scanned bad questions xD

Okay, not that the gauche effect question really was a good one, but it at least needed an answer somewhere xD

Wildcat

6:52 PM

In organic chemistry, hyperconjugation is the interaction of the electrons in a sigma bond (usually C–H or C–C) with an adjacent empty (or partially filled) non-bonding p-orbital, antibonding σ or π orbital, or filled π orbital, to give an extended molecular orbital that increases the stability of the system.

Mother of God! :O

Jan

What's wrong, cat? ó.ò

-1

Q: Can anyone give me detailed logical solution to my questions?

What is 1 amu? From where it is derived? Why it is compared with carbon-12? Why it was once compared with hydrogen-1? and now its not? Can anyone please explain me logically? And what would have happened if other elements were used?

> How about: No? x3

I was sooo~ tempted to just comment that ^^'

Wildcat

Nothing "wrong". I just trying to understand all these o-chem terms...

Wildcat

7:10 PM

Hyperconjugation is proposed by quantum mechanical modeling to be the correct explanation for the preference of the staggered conformation rather than the old textbook notion of steric hindrance.[5][6]

That is interesting. Suddenly, don't have time to read the articles. :(

inɒzɘmɒЯ.A.M

@Wildcat Ahh, so "steric hindrance" is the old version of hyperconjugation. I went thinking what the heck it's supposed to mean.

Jan

@inɒzɘmɒЯ.A.M No, it's not, unfortunately. ^^'

Hyperconjugation is what explains the stability of tertiary carbocations.

inɒzɘmɒЯ.A.M

What is it?

orthocresol

See @jan's answer, but replace the C-F σ* orbital with a p orbital in the positively charged carbon.

inɒzɘmɒЯ.A.M

Oh, she did post an answer!

Stack Exchange

7:49 PM

0

Q: Is there a way to save questions for later reading?

While I am trying to search from my questions, I come across many questions that interest me. I open them and often, I have to close my browser without reading many questions. I know I can use the "Open where left" option in my browser but that bugs me sometimes because of the large number of lin...

discussion feature-request

Jan

I just realised that @Wild's ava has an interesting effect: When kitty posts a one-liner, it looks like the head is slanting. When it's a longer block of text, it looks like the head is upright =D

inɒzɘmɒЯ.A.M

0

A: Is there a way to save questions for later reading?

Your best bet using Stack Exchange UI is favoriting questions. To do so, just click the star below the beautifully designed arrow signs of the questions. You can access the questions you favorited in your profile tab; here. However, I find this feature really annoying, because I have 224 favorit...

My answer is better than yours @Jan. ᕙ(⇀‸↼‶)ᕗ

@Jan I just realized that @Wild kitty's avatar has an interesting effect: It looks cute no matter what the size of the image is.

Jan

Just because you have links D=

Hehe, when @inɒzɘmɒЯ.A.M's and @ortho's avatars are in the list of people in the room next to each other, it looks like their molecules fuesd =D

inɒzɘmɒЯ.A.M

Yes. ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ

Jan

(Can anyone tell that I'm trying to procrastinate writing my weekly report? ^^')

inɒzɘmɒЯ.A.M

8:02 PM

@Jan Hmm, lemme check.

I mean, talk @Jan.

Jan

@inɒzɘmɒЯ.A.M Noo, don't type, or you'll destroy the fusion D=

Loong

@Jan either that or you are breathing solvent fumes

Jan

@Loong I would be concerned if I had because I used a lot of methanol today D=

inɒzɘmɒЯ.A.M

@Jan We look like a Ts(OH)^2-toluene. A three centered bond right there.

@Jan Today I did lab work, for the . . . hmm, second time. XD

Loong

@Jan as long as you can still recognize the avatars, you are not blind yet ;-)

Jan

8:07 PM

I keep thinking you have a periodic table there, @Loong xD

inɒzɘmɒЯ.A.M

And I got a brown hand with FeCl3 flavor.

@Jan @Loong reminds me of chocolate candies.

Jan

Chocolate? =D

Damnit, my Dess-Martin oxidation is about 70 % through, 3.5 hours after addition of more periodinane. Should I wait for it to complete or go home and work it up on Monday? *decisions*

Loong

in Photography 2015 Moderator Election, Oct 12 at 20:56, by AJ Henderson

@Loong - so how many people actually recognize your gravatar?

inɒzɘmɒЯ.A.M

@Loong One. @Martin. Because he recognizes all teh things.

> 526 helpful flags

Beat on that! (ノಠ益ಠ)ノ彡┻━┻

Mithoron

10:29 PM

4

Q: PV=nRT approximation on other planets?

In Chemistry class yesterday, I learned that real gasses with low atomic masses behave like an ideal gas at high temperatures and low pressure. Since on earth at sea level the pressure is close to $1\ \mathrm{atm}$ (which is a low pressure) and temperature is close to $288.15\ \mathrm K$ (high te...

gas-laws temperature pressure equation-of-state

Someone tell me that it would be better on Physics...

inɒzɘmɒЯ.A.M

@Mithoron Yeah, but meh, let it be.

Mithoron

Yep, it's at least no another homework dump, but illustrates most common misconception about atmospheric pressure on planets.

@inɒzɘmɒЯ.A.M Wildcat has probably best avatar here :)

Did I ping you more than once? Problem with connection :(

0

Q: NaOH + 2BaCl = NaCl2 + Ba2OH Balanced?

We are balancing equations and we got this one and were asked if its right. I assumed: Na (+) OH (-) + 2 Ba (4+) Cl (2-) = Na (+) Cl2 (2-) + Ba2 (4+) OH (-) So how can it be balanced as it needs the same amount of charges unless its an acid/base? I checked it with a online balancer and it says...

acid-base everyday-chemistry

XD, oh my...

orthocresol

11:59 PM

some interesting redox chemistry going on there...

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