Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Sonoris on November 22, 2013, 01:02:42 AM

Title: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 01:02:42 AM
Awful online homework, what else is new.


But afaik, these two don't even react? (http://puu.sh/5pGen.png) Solved

The textbook has nothing on alkynes + salts, just halides and stuff, so...?
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fpuu.sh%2F5pFXw.png&hash=86962ac7faff4a4de79f2d2ceb7e239d)

It also says nothing about alkynes + these two, unless you also have some halogen stuff laying around to react with first...
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fpuu.sh%2F5pGb2.png&hash=c233685140fb30171a7bedc58ad1de8b)

----------------------------------------
Edit2: What am I doing wrong here? It's neither of these apparently...?
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fpuu.sh%2F5pKKr.png&hash=92711ed09ec8ff3d8c7a8b3a539a42e0)
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fpuu.sh%2F5pKNW.png&hash=c6765364a926d5a015a41f63cf9d5e3c)
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 01:25:44 AM
So what is your question(s)? And have you any thoughts on the answers to your question(s)?
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 01:30:05 AM
So what is your question(s)? And have you any thoughts on the answers to your question(s)?

I have absolutely no idea how to go about these. The entire rest of the chapter questions I can do, but I can't find anything resembling these in the book. What is the mechanism going on here, and what would be the correct answer?
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 01:34:03 AM
Start with question A. It says acid/base reaction, so identify an acid and a base in that scheme.
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 01:51:08 AM
Start with question A. It says acid/base reaction, so identify an acid and a base in that scheme.
Acetylene is acidic, and NaOH is a base. Alright, so... an H can get pulled off the acetylene and there's gonna be ions and crap around and... ok, I got the right answer for it now. (quote from my textbook: "Because water is a stronger acid than acetylene, the hydroxide ion is not a strong enough base to convert a terminal alkyne to an alkyne anion" so uh, yeah...)

#2 still confuses me, but for #3 - is it just throwing a fit because I put NaNH2 and not Na+ and NH2- in the second box?
Title: Re: Alkyne rxns...?
Post by: Dan on November 22, 2013, 02:54:11 AM
Acetylene is acidic, and NaOH is a base. Alright, so... an H can get pulled off the acetylene and there's gonna be ions and crap around and... ok, I got the right answer for it now. (quote from my textbook: "Because water is a stronger acid than acetylene, the hydroxide ion is not a strong enough base to convert a terminal alkyne to an alkyne anion" so uh, yeah...)

There is no NaOH in the question.
Title: Re: Alkyne rxns...?
Post by: Archer on November 22, 2013, 02:57:52 AM

but for #3 - is it just throwing a fit because I put NaNH2 and not Na+ and NH2- in the second box?


Is that NH2- or NH2-?
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 03:04:38 AM
Acetylene is acidic, and NaOH is a base. Alright, so... an H can get pulled off the acetylene and there's gonna be ions and crap around and... ok, I got the right answer for it now. (quote from my textbook: "Because water is a stronger acid than acetylene, the hydroxide ion is not a strong enough base to convert a terminal alkyne to an alkyne anion" so uh, yeah...)

There is no NaOH in the question.
The now-solved, strikethrough question had NaOH
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 03:05:25 AM

but for #3 - is it just throwing a fit because I put NaNH2 and not Na+ and NH2- in the second box?


Is that NH2- or NH2-?
NH2-
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 03:22:10 AM
same thing which is the acid and which the base?


did you delete the previous one? If so please don't.
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 03:39:32 AM
same thing which is the acid and which the base?


did you delete the previous one? If so please don't.
No, I turned the statement into a link to the picture and put solved next to it - still there, just not obnoxiously huge.

Acetylene is still the acid, and the... lithium thing is the base I guess. If it's like the last one, ...oh, REALLY. That double bond in my answer should be a triple. Would that make it correct?

For the next one, with the alcohol + NaNH2 + NH3 - it won't accept any type of answer I think it might be (see Edit2, same issue)
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 03:42:10 AM
OK, the ethyl lithium is the base the acetylene the acid, so what could the products be?

Same for the alcohol, what are the products?
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 04:01:54 AM
Think about the very first question, what did you do to get the answer?
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 04:15:31 AM
OK, the ethyl lithium is the base the acetylene the acid, so what could the products be?

Same for the alcohol, what are the products?
For the lithium one - I want to say it'd be this (http://puu.sh/5pLn7.png), but in drawing it out I get this, but I guess the Li+ would go hang out with the C- (http://puu.sh/5pLD9.png)

For the -OH one, the OH compound is the base and the other is the acid. I still stand by the organic part of my answer, but... I guess there would just be Na+ around instead of NaNH2
edit: this answer for my -OH problem doesn't help for the edit to the main post I made, since neither of those are right and it just wanted the organics
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 04:20:02 AM
The acetylene one is now ok, you get
[C-]#C[H].[Li+]
and ethane.

Now do the same for the alcohol, replace the O-H by O-Na+ and the NH2- by NH3.
Title: Re: Alkyne rxns...?
Post by: Sonoris on November 22, 2013, 04:32:34 AM
The acetylene one is now ok, you get
[C-]#C[H].[Li+]
and ethane.

Now do the same for the alcohol, replace the O-H by O-Na+ and the NH2- by NH3.
So just this? (https://www.dropbox.com/s/latbatv745e1xfh/IMG_20131122_042708_650-1.jpg) Why doesn't this other example (http://puu.sh/5pKKr.png) do that? Should I have put the Na on the C-?

PS - thank you so much, btw @_@ hah
Title: Re: Alkyne rxns...?
Post by: discodermolide on November 22, 2013, 04:38:20 AM
Yes, associate the Na+ with the acetylene.
It's as simple as that!