The Periodic Table

1:03 AM

0

A: When is rotation around double bonds to form cis-trans isomers allowed?

Generally, all single bonds are said to permit free rotation while all double bonds are said to inhibit free rotation. This can actually be explained numerically as well: the rotation around the $\ce{O-O}$ bond in $\ce{H2O2}$ has an approximate rate constant of $2.0 \times 10^{8}~\mathrm{s^{-1}}$...

In case the people knowledgeable in group theory want to check the claim I made with which photon is able to excite pi->pi^*, please feel free and tell me how wrong I am ;)

DHMO

1:29 AM

@Jan thanks, but I believe that we say "I without you am like a singer without song" in English?

Jan

I would put commas in there. And I’m not fully sure but I feel the following is a slightly closer translation:

> Me without you is like a singer without a song.

DHMO

Also, I can't find "gestölpert" although google translates it to "stumped" or "stupid"

should it be gestolpert?

Jan

It’s tripped.

The infinitive is stölpern.

DHMO

I can't find stölpern either

not in Duden

Jan

Really …?

DHMO

1:34 AM

really

Jan

True story, I just checked all of German.SE’s common sources ô.o

DHMO

@Jan Wo bist du von?

Jan

Now I’m really confused. Maybe I should ask about it on German Language =D

DHMO

ja klar

@Jan "stolpern" means something similar though

Jan

However, I really stölper over stolper xD

DHMO

1:39 AM

@Jan Wuerdest du die Frage stellen?

Jan

I’m still going through posts of today on chem; after that travel, after that bed. Maybe tomorrow.

DHMO

ok

Jan

Why doesn’t \colspan exist in MathJax? D=

orthocresol

2:02 AM

Remind me not to answer questions by this guy again

Jan

Which guy?

orthocresol

Your question edit managed to invalidate two answers at one go. — orthocresol ♦ 5 mins ago

Jan

Oh, that one.

orthocresol

I have a nice diagram for the photochem question. I'll see if I can find it later ;)

Loong

@orthocresol Hm, if the current question really is what the user always intended, the first example using NaHCO3 was very unfortunate.

CowperKettle

2:21 AM

@Jan here's an animated version with subtitles

Киця кицюня - Пісні для дітей українською мовою - студія Ліра | ukrainian children's songs

►

good morning

7:23 here

Jan

@CowperKettle Unfortunately, the subtitles are Ukranian only, so I still don’t understand =C

Good evening; 3:30 here.

Jan

2:45 AM

0

A: What advantages does the mole have over counting large numbers using SI prefixes?

I am a chemist and I am still trying to understand why SI prefixes are not used by chemists. I am familiar with all the SI prefixes, but even if I was not familiar, I would prefer to learn a pair of universal prefixes rather than deal with the mole and all the issues, inconsistencies, and headac...

First line of the answer. … Seriously?

orthocresol

2:56 AM

Yeah, that was weird.

CowperKettle

3:26 AM

@paracresol - with your love for all things German, you might like the Barbie Museum

Rat Race (3/9) Movie CLIP - The Barbie Museum (2001) HD

►

user116211

3:44 AM

1

A: Does the free energy of the universe decrease for every process?

Didn't you ask the last question about this, too? The issue here is that when $\Delta G > 0$, the reaction is indeed non-spontaneous as written. If you wish to add energy to the system, for example, via electrolysis, you should include the additional changes in the computation of the free energy...

user116211

3:58 AM

This answer deserves more upvotes; though short, but it touched an important concept that the Second Law can indeed be reversed; it is not fundamental.

user116211

4:16 AM

@orthocresol If this has indeed happened, then this implies OP has changed his query he made in the earlier versions - it is highly discouraged; if you prefer, rollback to the previous version and leave a comment to make a new query separately.

orthocresol

4:34 AM

Rolling it back would borderline invalidate Jan's answer so...

user116211

okay.

user228700

4:51 AM

Yo, @paracresol: This is why I feel that Chennai is so much cooler (i.e. Warm (people) and kind) than Kerala:

user228700

user161117

waddap ppls

user161117

any cool chemistry stuff going on

user246160

Hi @StevenGrigsby :)

user246160

The chat room is relatively empty at this time !

user161117

4:55 AM

are you a bot lol

user246160

@StevenGrigsby No, I am a smart Artificial Intelligence :)

user246160

Better than the bots out there :P

user161117

Great, you can start proving your intelligence by installing GAMESS on my computer

user228700

x'D

user246160

@StevenGrigsby I don't prove my intelligence to random strangers on the net :P

user246160

4:58 AM

I am intelligent and I see no need to prove it :_D

user161117

pssshhh

user246160

So, where are you from, Steven ?

user161117

nowhere

user161117

which is why I'm here, so that I can say that I am from some where

user246160

Nowhere, Oklahoma

Nowhere is an unincorporated community in Caddo County, Oklahoma, United States. Nowhere is located at the southeast end of Fort Cobb Reservoir 5.5 miles (8.9 km) south-southwest of Albert and 14 miles (23 km) northwest of Anadarko. == References... ==

user246160

5:00 AM

This ^

user246160

or

user246160

Nowhere, Norfolk

According to 19th-century directories, Nowhere or No-Where is a marshy area by the River Bure where the villagers of Acle, Norfolk had salt-pans to produce salt for food preservation, etc. Originally an extra-parochial liberty it was formally incorporated into Acle parish in 1862 and the name no longer appears in maps and gazetteers. In 1861 there were four inhabited houses and 16 people. == External links == Page at GenUKI quoting directories such as: White's History, Gazetteer & Directory of Norfolk, 1883 Kelly's Directory of Norfolk, 1904 Acle (Det. No. 2) and Acle (Det. No. 3), the Ordnance...

user161117

yes

user246160

Oh, good to know, merkan :)

user161117

What sorta chemistry do you like

user246160

5:01 AM

Any undergraduate level chemistry topic

user246160

Organic, Inorganic , Physical

user246160

You?

user161117

Organic and Physical mostly

user246160

I am in final year of high school of Artificial Intelligences :-D

user161117

right on robot kid

user246160

5:03 AM

@StevenGrigsby And and what level are you learning chemistry ?

user161117

I'm procrastinating applying to graduate school at the moment, I got my bachelor's in chemistry 2 years ago

user161117

at the moment I was looking for someone to throw around ideas at understanding why this reaction goes the way it does

user161117

name-reaction.com/mukaiyama-aldol-addition

user161117

I think I'm getting a bit rusty with my organic

user246160

@StevenGrigsby As a matter of fact I am robot kid made of flesh and blood and all organs that humans have...and I am fairly advanced compared to puny humans ;-D........ btw what were you doing for 2 years ? :-O

user161117

5:05 AM

but I don't see any particularly good reason why the aldehyde oxygen acts as a nucleophile and kicks out the Cl from TiCl4

user246160

@StevenGrigsby I am seeing the reaction. Wait a min.

user161117

relaxing, studying number theory

user161117

tensors

user161117

whatever I felt like mostly

user161117

browsing dank memes

user161117

5:06 AM

learning a bit more QM to feel less stupid about what I was talking about, stuff like that

user161117

but enough about me, I am boring, I am more interested in this mechanism

user246160

Well, aldehyde oxygen is the only legit nucleophile I can see in the mechanism. Moreover, TiCl4 does have vacant orbitals to allow the attack. Cl is a good leaving group, better than the aldehyde oxygen anyway.

user161117

Oh, what do you mean by "TiCl4 does have vacant orbitals"

user161117

what makes you say that

user246160

Titanium configuration- [Ar] 3d2 4s2

user246160

5:12 AM

Now, try writing it for Ti(+4)

user161117

Oh ok

user161117

I thought you meant something a bit more involved than that

user246160

Yes, the antibonding orbitals allow the attack by another nucleophile. Otherwise it would not have been possible. Another reason is the high charge density of Ti(+4)

user161117

I guess you're judging Cl- as being a better leaving group than the aldehyde just on account of their pKas or something else

user161117

Yeah, it's definitely a good lewis acid, pretty well oxidized there

user246160

5:15 AM

Leaving group

In chemistry, a leaving group is a molecular fragment that departs with a pair of electrons in heterolytic bond cleavage. Leaving groups can be anions or neutral molecules, but in either case it is crucial that the leaving group be able to stabilize the additional electron density that results from bond heterolysis. Common anionic leaving groups are halides such as Cl−, Br−, and I−, and sulfonate esters such as tosylate (TsO−). Fluoride (F−) functions as a leaving group in the nerve-agent sarin gas. Common neutral molecule leaving groups are water and ammonia. == Leaving Group Ability == ...

user246160

......en.wikipedia.org/wiki/Leaving_group#Leaving_Group_Ability

user246160

See the chart given. You will find that Cl is one of the best LGs

user161117

of course it's a great LG

user161117

but do you have a specific trend in mind or did you just memorize this table?

user246160

Actually there are several factors which make a LG good or bad

user246160

5:17 AM

Including resonance effects and size of atom

user246160

vacant orbital, etc

user161117

sure, so what makes you say Cl- is a better leaving group than the aldehyde?

user161117

I would say they're fairly similar

user246160

Which is bigger in size? O or Cl ?

user246160

Which has higher charge density ?

user246160

5:22 AM

Which has more vacant orbitals to hold electron lone pair ?

user161117

they're fairly similar in size on their own, Cl- will have higher charge density

user161117

seems to me the aldehyde has an inductive stabilizing effect, it's bulkier

user161117

it's electrically neutral

user246160

@StevenGrigsby Are you kidding me ? :P

user246160

one is 60 pm

user161117

5:23 AM

?

user246160

and the other is 175 pm

user246160

They have large difference in size

user161117

oh right

user161117

Cl is larger yeah

user246160

O has greater charge density

user161117

5:24 AM

but O is attached to stuff

user246160

@StevenGrigsby so ?

user246160

still it has a much higher charge density

user161117

so the pi bond and the rest of the molecule won't do anything as far as making the oxygen softer?

user161117

just seems to me that the Cl- that leaves will be leaving with an electric charge while the aldehyde is neutral

user246160

@StevenGrigsby It will, but not much. If it was a carboxylic acid with the O conjugated then we could'nt say so. Instead of aldehyde if you took any carboxylic acid as nucleophile, then the attack on TiCl4 would not happen

user246160

5:29 AM

@StevenGrigsby Cl- prefers forward direction as Si-Cl compound is stable

user246160

Si-Cl compound is formed finally in the reaction as you can see

user161117

I guess I'm still a bit put off since the pKa of HCl is about -7 and the pKa of a protonated ketone is about -7.3, which would mean that a protonated aldehyde would be even less

user161117

so I'm sorta imagining the equilibrium not shifting that way

user246160

But why are you comparing it with HCl ?

user161117

sure, so is there any reason to believe the Cl- attacking carbonyl the aldehyde attached to the TiCl3 is unlikely

user246160

5:32 AM

The medium is not even acidic

user161117

just by analogy of instead of H+ being what's attached, it's +TiCl3 that's attached

user161117

I don't think it's entirely unreasonable to look at as a rough guess, nucleophilicity and basicity aren't unrelated

user246160

I will sum up by saying: 1) Si-Cl bonds are more stable than that Ti-Cl bonds which prefers the forward reaction 2) Nucleophilicities and basicities do not parallel in case the attacking atoms are different 3) Leaving group ability is dependent on many factors out of which the major factor is charge density and here O has a higher charge density than Cl

user161117

Sure, sounds like what you've been saying

user246160

If you are still not convinced you can ask on the main site :)

user246160

5:39 AM

I have some work to do right now

user161117

Woah you sure are impatient

user246160

See you :)

user161117

bye bye

user246160

Bye!

user161117

I'm not really looking for answers, thanks though

user161117

5:40 AM

you've made some nice suggestions

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