[steak]

Isn't that name ambiguous?  Wouldn't there have to be numbers indicating where the two double bonds are?   E.G.       c=c=c-c  would be 1,2-butadiene   and  c=c-c=c would be 1,3-butadiene.  Or does the name, "butadiene" somehow imply where the bonds are?  I'm trying to synthesize hex-2-en-5-yne from "butadiene" (that's what my professor has on this worksheet), and I'm at a serious stand-still.  Any word on my questions, or on the reaction is sincerely appreciated.

[KritikalMass]

Based off of this Wiki article I'd say they are refering to 1,3-butadiene

http://en.wikipedia.org/wiki/1,3-Butadiene

[nj_bartel]

1,3-butadiene is what's almost definitely being referred to if numbers aren't given.  Allenes aren't a super common set of compounds, and the numbering would definitely be given.

[steak]

Thank you for the posts.  I saw the wiki article, too.  I think it's 1,3-butadiene, also.  In either case, I used the ambiguity of it's name to my advantage in the sythesis, and went with 1,2-butadiene.  I couldn't figure how to use the 1,3 isomer.  Oh well.   

[jj74]

For your synthesis, I’m not sure but maybe a reaction of acetylide ion with 1,3 could be OK