A random chemistry question

[Fortuna]

I'm studying high school organic chemistry at school at the moment (read: I just read the organic chemistry chapter of an old Atkin's General Chemistry book), and I've been wondering about something. Both my teacher and the book proved singularly unhelpful, so I turn to the playground.

First question, which I need the answer to to phrase the second question: if we have a straight-chain hydrocarbon C5H8, in which there are two carbon-carbon double bonds instead of a carbon-carbon triple bond, how do we name it? How do we distinguish in the name between the two structural isomers?

[Astrella]

I believe, if for example the double bonds are at the ends of the molecule it would be 1,4-dipentene. (It's been a few years since I had to do any naming of molecules, so don't take my word on it.)

[Fortuna]

That sounds plausible. My next question is significantly more complicated.

Take, for example, 1,2,4,5-tetrachloro-1,4-dipentene. Is it possible to distinguish between the four (by my count) geometric isomers in naming this molecule? If so, how?

[Iruka]

With geometric isomers, do you mean stereoisomers?

[Fortuna]

Yes, I think. Geometric as opposed to structural.

[Teddy]

That sounds plausible. My next question is significantly more complicated.

Take, for example, 1,2,4,5-tetrachloro-1,4-dipentene. Is it possible to distinguish between the four (by my count) geometric isomers in naming this molecule? If so, how?

I counted 3: Cis-Cis, Cis-Trans and Trans-Trans (Trans-Cis is the same as Cis-Trans turned 180 degrees). I'm not sure on how to distinguish them, though

[Elder Tsofu]

Like this?

Depending on how the substitutes sit on the two double bound C.
E= opposite side
Z= same side (zuzammen)

http://i681.photobucket.com/albums/vv173/Tsofu/1.png

[Fortuna]

That makes a good deal of sense. Thank you. Where did you get the images?

[Elder Tsofu]

Created it in Symyx draw, nifty (and free) tool when you have to draw your own structures.
http://www.symyx.com/downloads/

But it seems like I was ninjad by Teddy, giving the same answer. :smalltongue:

[Eldan]

Yeah. The two possible terminologies are cis/trans or E/Z, depending what else is on the chain.

Oh god horrible memories of Organic chem II.

[Nomrom]

In about three hours, I'll be taking my ochem 2 final. I can't wait to be done with the class. Of course, In three weeks I'll be starting another chemistry course, so I guess it never really ends.

[Eldan]

It did for me. But then, I'm not actually a chemist.

It was just that biologists were forced to take Chemistry I, Organic Chemistry I+II, Physical Chemistry I+II, Analytical Chemistry I+II and one other I can't remember the exact name off during the first two years. And most likely, I'll never use most if it ever again.

[Asta Kask]

Am I the only person in the world to like Organic Chemistry?

[GrlumpTheElder]

Am I the only person in the world to like Organic Chemistry?

I enjoyed it, when I did it.


I counted 3: Cis-Cis, Cis-Trans and Trans-Trans (Trans-Cis is the same as Cis-Trans turned 180 degrees). I'm not sure on how to distinguish them, though

Hmm, never come across Cis-Cis or Trans-Trans before.

[mangosta71]

Hmm, never come across Cis-Cis or Trans-Trans before.

It's a less common conformation because it's a higher energy state.

[Elder Tsofu]

Am I the only person in the world to like Organic Chemistry?

Loved it, thinking of getting a master in chemistry - or maybe a bachelor.
Just for fun.

[Lioness]

Am I the only person in the world to like Organic Chemistry?

Nope. I loves it.

Forget all the stupid analytical stuff, that requires maths, I like organic.

[Don Julio Anejo]

Oh god I have my analytical chem final next Wednesday and my organic II next Friday.. :eek:

Anyone care to send me some cyanide? :annoyed:

[Eldan]

If you want cyanide, just eat some raw cassava.

Anyway, I preferred analytical chemistry over organic or inorganic. At least our exam was a three hour long logic puzzle, and I'm good at those.

[Teddy]

Am I the only person in the world to like Organic Chemistry?

I did. I quite liked how heavily structured it was. Then, after we finished the Organic Chemistry, we went on to Biologic Macro-Molecules, where everything is abbreviated and made as uncomplicated as possible. The difference was quite confusing (and I must say that I liked the Organic Chemistry better, just because of that).

[Eldan]

After a while it just gets too tedious for biochemists to name everything correctly. Yes, it's abbreviations of abbreviations of abbreviations, but it's just the only way that works.
Though in the end, they usually end up with three letters and two numbers.

[GrlumpTheElder]

Forget all the stupid analytical stuff, that requires maths, I like organic.


I still get confused with the nmr...

Infrared Spec is ok

[Teddy]

After a while it just gets too tedious for biochemists to name everything correctly. Yes, it's abbreviations of abbreviations of abbreviations, but it's just the only way that works.
Though in the end, they usually end up with three letters and two numbers.

Yeah, I know that, and I think I said something along that line when I explained the difference between organic chemistry and biochemistry to my parents, and pretty much everyone else who was willing to listen. :smallamused:

[Don Julio Anejo]

Anyway, I preferred analytical chemistry over organic or inorganic. At least our exam was a three hour long logic puzzle, and I'm good at those.
Organic is OK for us, it's going to be all reaction mechanisms. My prof is pretty anal about little electron pushing arrows but in the end it's just going to be memorizing a few dozen mechanisms and the exam will involve stuff like "how would you make this molecule" or "show a Robinson Annulation for this thingimajig from these two whatchamacallits"

Analytical on the other hand... I'll bet you my right hand 75% of it will involve electrochemistry (I HATE electrochemistry. Sorry, didn't emphasize it enough. I despise electrochemistry). I can probably use my TI-89 but it ain't gonna help me much if I still get confused as to which side is the anode or the cathode and which way the minus sign goes. That's after like... 5 classes that involved it. The other 25% is going to be on systematic treatment of equilibrium. It's as much fun as it sounds, but you probably already know that.

[Lioness]

Analytical chemistry-wise, I hate Atomic Ab(d?)sorption spectroscopy and chromatography. The teacher never really explained it properly, so I don't understand it at all.

Equilibrium is fine, because I've memorised Le Chatelier's principle, and that's pretty much all we get tested on. Electrochemistry...again, not so great, but manageable. I get confused as well.

[Eldan]

Organic is OK for us, it's going to be all reaction mechanisms. My prof is pretty anal about little electron pushing arrows but in the end it's just going to be memorizing a few dozen mechanisms and the exam will involve stuff like "how would you make this molecule" or "show a Robinson Annulation for this thingimajig from these two whatchamacallits"

Analytical on the other hand... I'll bet you my right hand 75% of it will involve electrochemistry (I HATE electrochemistry. Sorry, didn't emphasize it enough. I despise electrochemistry). I can probably use my TI-89 but it ain't gonna help me much if I still get confused as to which side is the anode or the cathode and which way the minus sign goes. That's after like... 5 classes that involved it. The other 25% is going to be on systematic treatment of equilibrium. It's as much fun as it sounds, but you probably already know that.

Ah. Our analytical course mainly involved "here's the result of four different analyses (proton NMR, infrared, mass and so on), draw a possible structure for the entire molecule". Got difficult, but a logical process, at least.

Our organic chem exam was pretty much the same either "You have this, you want that, what do you do", "Do an X reaction on this molecule pair", "Show this reaction in detail", "What's the name of this exam" and so on. I just dislike memorizing dozens of mechanisms and functional groups. Or pretty much memorizing any list of objects.

[Adlan]

I counted 3: Cis-Cis, Cis-Trans and Trans-Trans (Trans-Cis is the same as Cis-Trans turned 180 degrees). I'm not sure on how to distinguish them, though

Distinguish them by optical activity, seperate them by chromatography.

[Teddy]

Distinguish them by optical activity, seperate them by chromatography.

Actually, that was just a poor wording for "I don't know how to name the difference between them.".

[Elder Tsofu]

Add an R and an S and I think he might have it Teddy. :smalltongue:

[Teddy]

Add an R and an S and I think he might have it Teddy. :smalltongue:

Eh, what? :smallconfused:

[Don Julio Anejo]

Ah. Our analytical course mainly involved "here's the result of four different analyses (proton NMR, infrared, mass and so on), draw a possible structure for the entire molecule". Got difficult, but a logical process, at least.
We do this for organic. Dunno, but I actually find it pretty fun. Better than electrochemistry or memorizing a list of objects.

Add an R and an S and I think he might have it Teddy. :smalltongue:
Uhm there's nowhere to stick an R or an S in there. All the carbons are either sp2 or have identical groups attached.

Analytical chemistry-wise, I hate Atomic Ab(d?)sorption spectroscopy and chromatography. The teacher never really explained it properly, so I don't understand it at all.

Equilibrium is fine, because I've memorised Le Chatelier's principle, and that's pretty much all we get tested on. Electrochemistry...again, not so great, but manageable. I get confused as well.
Damn lucky :wink:
Systematic treatment of equilibrium = you get something like a triprotic acid with no pKa for any dissociation, you get an electric cell that uses that acid and then by some unknown means you have to calculate Kf for metal-EDTA titration complex and you don't even know where those came from since the original problem only involved an acid and a cell.

[Elder Tsofu]

Uhm there's nowhere to stick an R or an S in there. All the carbons are either sp2 or have identical groups attached.

Ha, correct.
Man I want back to my dear chemistry. ^^

[Don Julio Anejo]

Like this?

Depending on how the substitutes sit on the two double bound C.
E= opposite side
Z= same side (zuzammen)

http://i681.photobucket.com/albums/vv173/Tsofu/1.png
BTW something I realized. For this particular molecule, there's only two stereoisomers. The other two are simply the original isomers flipped upside down. Only works because it's symmetric though, change one of the chlorines to 3-carbon and suddenly you've got both enantiomers and 4 E/Z configurations.

[Teddy]

BTW something I realized. For this particular molecule, there's only two stereoisomers. The other two are simply the original isomers flipped upside down. Only works because it's symmetric though, change one of the chlorines to 3-carbon and suddenly you've got both enantiomers and 4 E/Z configurations.

No, there are three:

Cis-Cis, Trans-Trans and 2 Cis-Trans.

[Eldan]

Yeah, not the same at all. Watch the chlorines.