The Periodic Table - 2016-10-06 (page 1 of 2)

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pentavalentcarbon

2:47 AM

user image

Only chance at the review queue is when everyone else is asleep, it seems

pentavalentcarbon

2:58 AM

Better wake up early and write the questionnaire.

4 hours later…

6:40 AM

Hey @orthocresol

I'm freezing here

In Australia?

Think I'll go back to sleep.

I didn't know that was possible

Cya

6:41 AM

Ha, alright

2 hours later…

Martin - マーチン

8:14 AM

-1

Q: Why is lemon mixed with water considered alkalizing water?

The benefits and facts of alkaline water are often skewed due to the marketing of companies and uneducated hype for the innocent idea of unlimited potential. I wanted to know the specific reactions occurring when mixing water and fresh lemon slices that lead to water becoming alkalized (higher in...

everyday-chemistry

so sad to see that downvoted to hell...

the boiling points of the straight chain n-alkyl alcohols have a trend, but their melting points are all over the place... why?

8:34 AM

0

A: Why does hyperconjugation help for ring cleavage?

This is a bit late, but my instinct tells me you form the 1,3 diradical. The fusion to a cyclopropane seems pretty reasonable. The alkene is formed from a 1,2-hydrogen atom shift (I admit, this is a strange abstraction), but the formation of the alkene (and the fact that this is flash vacuum pyro...

An honest answer on a mechanism question from an organic chemist should always start from "my instinct tells me". XD CC @Jan

1 hour later…

9:50 AM

Mass chromatogram

A mass chromatogram is a representation of mass spectrometry data as a chromatogram, where the x-axis represents time and the y-axis represents signal intensity. The source data contains mass information; however, it is not graphically represented in a mass chromatogram in favor of visualizing signal intensity versus time. The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography, such as in liquid chromatography-mass spectrometry or gas chromatography-mass spectrometry. In this case, the x-axis represents retention tim...

How is it different from just "chromatogram"?

@CowperKettle What "just chromatogram"?

@Mithoron Just a chromatogram

The usual thing

Where is the difference?

X axis: time, Y axis: signal intensity

The same with mass-chromatogram

sigh

@Wildcat I actually don't like the title. If there's no or little hyperconjugative effect then it's outright wrong. Should probably be something more generic like "Why does isotopic substitution affect the product distribution of blah blah blah".

@Mithoron Is there a good explanation anywhere online?

The Wikipedia article is horrible

9:55 AM

Concept check:
Solid, liquid, and gas differ in the bond forming and bond breaking between molecules.

For solid and gas, it is a stable equilibrium. In solid, all possible bonds are formed; in gas all possible bonds are broken. I do not mean all bonds are broken, but the bonds that can be broken are all broken. For example, in the gas phase of AlCl3, there may be a dimer.

For liquid, it is a dynamic equilibrium, since bonds break and form readily. The equilibrium position is governed by temperature. At the melting point, all bonds are formed. At the boiling point, all bonds are broken. At…

Please check if my concept contains any mistake, thank you very much in advance.

I expect it to contain quite a lot of mistakes.

@CowperKettle I can't agree with you on that

@Wildcat Right now it seems as if "hyperconjugation -> ring cleavage" is some generic conclusion that can be applied to all ring cleavage reactions, which is probably not true.

@Mithoron I've read the introductory paragraph several times, and it says nowhere how exactly a mass chromatogram differs from a simple chromatogram

OP last seen March 14... Maybe I will just take the liberty to edit it myself some time.

> A mass chromatogram is a representation of mass spectrometry data as a chromatogram, where the x-axis represents time and the y-axis represents signal intensity.[1] The source data contains mass information; however, it is not graphically represented in a mass chromatogram in favor of visualizing signal intensity versus time.

O_O

This basically says that Mass-chromo = Chromo

9:58 AM

@orthocresol could you please check my concept? thank you

> The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography, such as in liquid chromatography-mass spectrometry or gas chromatography-mass spectrometry. In this case, the x-axis represents retention time, analogous to any other chromatogram. The y-axis represents signal intensity or relative signal intensity.

Here it just repeats the first two sentences.

No, I don't have time.

@CowperKettle could you help me please?

> A MC (Mass Chromatogram) is a chromatogram for a specific mass, which is produced by connecting the spectral points of the same mass number. The figure shows the m/z 117 mass chromatogram. A MC sometimes provides us with a chromatogram of a single component in a mixed sample with less noise. (A **totally** different definition from Shimadzu)
http://www.shimadzu.com/an/mc.html

@DHMO No, sorry

Maybe I should ask on main site what a mass-chromatogram actually is.

@CowperKettle Well you should have answered properly what would be your "just chomatogram"

10:02 AM

@Mithoron A chromatogram is the visual output of the chromatograph. In the case of an optimal separation, different peaks or patterns on the chromatogram correspond to different components of the separated mixture. Plotted on the x-axis is the retention time and plotted on the y-axis a signal (for example obtained by a spectrophotometer, mass spectrometer or a variety of other detectors) corresponding to the response created by the analytes exiting the system.

So it's the same as "mass chromatogram", if Wikipedia is to be believed

Geez, it's simply a type of chromatogram!

But what type? How is it different?

There must be a human-readable definition somewhere.

Subtype

@orthocresol agree :)

@Wildcat could you help me check it please?

10:06 AM

It's simply a type of chromatogram, diffrenent from for example chomatogram from TLC, that's it! What is here to even ask about

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6

Q: Reaction intermediates of MnO2 catalyzed H2O2 decomposition reaction

Manganese dioxide catalyzes the decomposition of hydrogen peroxide to water and oxygen gas. But what are the intermediates in this catalyzed reaction?

inorganic-chemistry catalysis

@Mithoron Different in what?

Where is the difference?

@DHMO hi! what do i need to check? :O

@Wildcat 13 minutes ago in this room

XX:55 where XX is the last hour

Okay I'll try to find out more.. no answer thus far

10:11 AM

@CowperKettle MS gives you rather different output then TLC don't you think?

@DHMO, hmmm... I don't know.

@Wildcat ok, thanks

cats are the best

I mean, solids, liquids and gases differ in strengths of intermolecular bonds.

That is essentially it.

Intermolecular bonds are, in a sense, always there.

@Mithoron I know that. But what has it to do with a mass-chromatogarm, if, according to Wikipedia, it does not show the MS data?

It is just that they are very weak in gases.

intermolecular interactions

is even better

than intermolecular bonds

10:15 AM

@Wildcat that's a new perspective to me... but is liquid in a dynamic equilibrium or are the bond strengths constant? if it is the latter then i do not see how molecules can slide...

@DHMO first, the concept of a chemical bond is not sharply defined

also, AlCl2 has two gas phases... one with the dimer and one with the mononer

@Wildcat well, i meant internolecular attractions

that's what i refer to bond

for brevity

11:11 AM

@ortho are you there?

No @ortho, no fun. :|

pH13 - Yet another Philipp

we need that orthocorrection immediately!

@pH13 what for?

pH13 - Yet another Philipp

everything

11:51 AM

3

Q: Corey-Schmidt oxidation of primary alcohols

Why does pyridinium dichromate (PDC) in dimethylformamide (DMF) oxidize alcohols to acids while in methylene chloride the oxidation stops at the aldehyde level?

organic-chemistry reaction-mechanism

Nahhh. Wrong answer, obviously. The right one should start with "my instinct tells me". XD

12:52 PM

acdlabs.com/iupac/nomenclature/93/r93_81.htm

Did it forget to mention that buta + ene gives butene instead of butaene, or am I missing something?

@Loong

@NilayGhosh welcome back

@Wildcat Yes, I heard a meow in the dark calling for me?

@orthocresol :D just wanted to ask you: did you know about different conventions for inner product in phys and math communities I mentioned there?

1:10 PM

@DHMO Strictly speaking, the "ene" part replaces the "ane" ending of the saturated parent structure.

@Loong but we have butadiene

@Wildcat No, I actually didn't know about that. But I am not surprised to hear of such a thing.

@DHMO In this case, if you have multiplying prefix and locants, you insert the letter 'a'.

7

A: Naming unsaturated hydrocarbons

According to the general methodology described in the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), a double bond is expressed by changing the ending ‘ane’ of the name of the corresponding saturated parent structure to ‘ene’. ...

@Loong So this is not related to r017

R-0.1.7

I thought the original form is buta-

@DHMO The old rule was R-3.1.1: acdlabs.com/iupac/nomenclature/93/r93_280.htm

In the current rules, it's P-31.1.1.1 and P-31.1.1.2.

1:21 PM

@Loong how new is that?

@DHMO The 1993 recommendations had the old wording of this rule; the new wording appears in the 2013 recommendations. I don't know when it was introduced. The 1998 guide does not mention the complete rule.

@Loong Oh... alright, I think I'll quote the new version. I didn't know that R- is 1993

@DHMO You can see it in the full path name: http://www.acdlabs.com/iupac/nomenclature/93/r93_280.htm refers to the 1993 recommendations; http://www.acdlabs.com/iupac/nomenclature/79/r79_53.htm refers to the 1979 recommendations.

@Loong do you have the link to 2013?

@DHMO Unfortunately, there is no free version of the 2013 recommendations: pubs.rsc.org/en/content/ebook/978-0-85404-182-4#!divbookcontent

1:33 PM

@Loong not even through sci-hub?

@Loong There is no free legal version. However, that thing has more than 1500 pages, so it would be difficult to distribute anyway.

@Loong sci-hub is legal

pH13 - Yet another Philipp

@DHMO why do you think that?

2 days ago, by MAFIA36790

@DHMO The site is not illegal.

Not so sure about that.

1:40 PM

2 days ago, by CowperKettle

> In her defense Alexandra Elbakyan has cited Article 27 (1.) of the UN Declaration of Human Rights "to share in scientific advancement and its benefits", which she claims is hindered by publishers demanding payment despite putting in minimal effort in publishing the academic papers, which she says are essentially donated by researchers.

pH13 - Yet another Philipp

@DHMO well, then the question has to go to @MAFIA36790 ... but the question stays

> The site is currently involved in a legal case with Elsevier: Elsevier et al. v. Sci-Hub et al.[26] Court documents which discuss technical details of how the site functions are available to the public.[27] Elsevier claims that Sci-Hub illegally accesses accounts of students and academic institutions to provide free access to articles through their platform ScienceDirect.

if it was illegal, I wouldn't be able to talk about it, right

pH13 - Yet another Philipp

no

@pH13-YetanotherPhilipp ?

pH13 - Yet another Philipp

it is unclear if it is illegal or legal. therefore those courts have to decide about it. as long as there is no decision, we simply don’t now it

1:43 PM

@pH13-YetanotherPhilipp alright

@pH13-YetanotherPhilipp In 2015 a New York court ruled that Sci-Hub violates US copyright law.

However, that doesn’t change anything for sci hub in practice.

pH13 - Yet another Philipp

the servers are somewhere in kazakhstan ... us law is not so important there

@Loong So, maybe you could answer the question using 2013 standard?

@orthocresol it took me some time few years ago to realise that :D

@DHMO Sure, however that wouldn't be so much different from my other answer. Maybe I coul put more emphasis on the multiplying prefix.

1:56 PM

@Loong sure. the table should be identical, right

user116211

2 days ago, by MAFIA36790

Sci-Hub is an online search engine with over 58,000,000 academic papers and articles available for direct download, bypassing publisher paywalls. New papers are uploaded daily when accessed through educational institution proxies, and papers that have been accessed through Sci-Hub are stored in the LibGen repository. Sci-hub was founded by Kazakh graduate student Alexandra Elbakyan in 2011, as a reaction to the high cost of research papers behind paywalls, typically US$30 each when bought on a per-paper basis. Sci-Hub follows the general open access movement of the 1990s, and a number of smaller...

user116211

@pH13-YetanotherPhilipp And I just meant it is not illegal in my country.

pH13 - Yet another Philipp

@MAFIA36790 that’s possible

user116211

Although I can't stand along this statement too strongly, there are still no legal actions against Sci-Hub in India. On the contrary, it's quite famous and extensively used.

@orthocresol I notice that there is no Holy Thin Space of Antioch in these posts. ;-)

2:01 PM

@Loong heh, what does that mean?

Sep 21 at 13:34, by orthocresol

@Loong I put in my \,'s religiously now!

:O I didn't notice that there was no space

Blasphemy!

Firefox autocorrect does not recognize "covalent"...

pH13 - Yet another Philipp

9 mins ago, by Loong

Blasphemy!

2:16 PM

user image

How do we know that 2a1 is NBMO?

Because there is an interaction with three orbitals which create one bonding, one non bonding and one anti bonding

So 1a1 is BOM, 2a1 is NBMO and 3a1 is ABMO

2a1 results of the effect of antibonding between 2s and phi1 and bonding between phi1 and 2pz

@9-BBN is this a law?

three AOs must create 1xBMO + 1xNBMO + 1xABMO?

I don't if it is a law, but if you draw the MO you'll see the MO will have not a big electronic dentity in the middle hence the bond is very weak and then NBMO

In this case

@9-BBN what is the NBMO actually?

well, I know that two AOs must create 1xBMO + 1xABMO, right

or 2xNBMO

is there a rule?

It is a MO which not unstabilized the system nor stabilizied it too so the energy of the system is not quite modified with this interaction

user image

Look at (II)

At the right

The interaction between the atoms is very weak because the "recouvrement" (don't know the english noun) (Sij integral) is very small as you can see

2:30 PM

@9-BBN oh, you're french

What is written is maybe false. I did that to ask a question here

your handwriting is good by the way

Yes I am

Why do French people should have a bad handwritting? :P

pH13 - Yet another Philipp

@9-BBN no one said that

@pH13-YetanotherPhilipp exactly

2:31 PM

@pH13-YetanotherPhilipp don't worry ;)

Also I'm still waiting @Jan to answer my question in a comprehensive way haha

So in english Sij is the integral of ??? ?

@9-BBN Is there a way to identify NBMO from the probability diagram / y a-t-il un methode pour identifier les NBMOs du diagramme de probabilite?

user116211

@9-BBN overlap integral.

What do you mean by probability "diagram" ?

@MAFIA36790 thank you

@9-BBN well, the images of the MOs / les images des MOs

I understand english ;)

2:35 PM

@9-BBN alright

But I don't understand what you mean. :P Well is that on the diagram I drew for LiH for example?

user image

@9-BBN these for example

user116211

@9-BBN To be a mathematician, you must have to know French.

Oh I guess the answer might be yes let me think

@MAFIA36790 oh really?

user116211

@9-BBN Yes. Thanks to Bourbaki.

user116211

2:38 PM

Well, that's only one reason.

user116211

There are many that will convince a to-be mathematician to learn French.

@MAFIA36790 this guy is a myth ?

user116211

@9-BBN No.

user116211

@9-BBN Should be these; in fact that is a pseudonym.

user116211

A whole group worked under the name of Nicolas Bourbaki.

2:40 PM

@DHMO well in fact on those diagram you need to draw like on the (a) but with a very thin bond between the two atoms

user116211

And the interesting fact is that he is still alive.

user116211

@Rubisco o/

Yo

@DHMO but I've never seen that

@9-BBN but you just drew 3 of them

2:42 PM

@MAFIA36790 oh ok and so what is the reason to learn french ?

@DHMO I drew a MO-diagram

user116211

@9-BBN There are many maths papers which don't see the light of translation :(

@9-BBN I mean the molecular orbitals

you drew three molecular orbitals

@9-BBN a number in the beginning of a name is creepy.

Yes but I don't know what you wanted me to do more ?

@Rubisco why creepy?

@9-BBN Because it's creepy

2:44 PM

9BBN is cool

No, it's warm.

I was expecting to see another nominee.

Guess we're not that lucky

3.5k 1 19

physical-chemistry spectroscopy thermodynamics bond energy homework quantum-chemistry

user116211

Hmm, the nomination seems to be cool here; no drama ;/ But that's good. Physics saw much more.

@Jan a sock with 3k rep is too much.

@MAFIA36790 Physicists . . .

@DHMO look

pH13 - Yet another Philipp

@Rubisco and how about the middle/end?

2:48 PM

user image

@9-BBN en train de voir

This one is bonding

@pH13-YetanotherPhilipp Not so much

@9-BBN s + pz

pH13 - Yet another Philipp

@Rubisco damn

2:48 PM

Because the electronic density is big between the two atoms

user116211

@Rubisco What does experimental chemical physicist mean? Totally new to me.

next :

user image

What the ping

@9-BBN what is this

user116211

@Rubisco I'm hearing no sound of pinging.

2:49 PM

That's because you're pinging me

user116211

@Rubisco No. no...

user116211

When someone pings me, I hear a sound; but it's not happening lately.

Somebody get MAF off the keyboard

My speakers are exploding.

user116211

._.

@9-BBN seriously, this looks like s-pz but this does not look like s-pz

2:51 PM

Dear diary,
Today I didn't have to edit a new user's question body. I feel life has finally smiled at me.
The End

2

Well no the next one is not a good example because the website doesn't make what I would like to show you I need to find an other example

By the way what I drew with hand is the easy way to get a result without make calculus. It is based on it but we did some approximations

Lol

hi, and welcome to chemistry StackExchange. Have a look at the wikipedia page, you should be able to answer your question. google.co.uk/… — porphyrin 6 mins ago

@9-BBN maybe you should use your hand-drawn MOs to explain instead

But explain what ?

ugh

well

explain how we can identify NBMO

2:54 PM

By looking at the size of the lobes

and how far they are

If you have a + + or a - - interaction with two small lobes as I drew it must be a non bonding one

@Loong Haha... I haven't been paying much attention to the questions these two days. As I suspected, life has gotten much busier

if you have a + - or a - + interaction it is always anti (I have no counterexample in head)

@9-BBN I thought + + is bonding

Yes

It is bonding if S is "big"

it is not if S is close to 0

@9-BBN I don't understand

I know what S means

what about antibonding?

2:58 PM

If S = 0 there is no bond, if S=0.001 maybe it could have a bond but too much weak to be consider as stabilizing the system i.e. create a bonding bond

You will say with anti S = 0 too. Yes but you see it is anti bonding because of the signs

@9-BBN :o

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