[Fry]

The synthesis of azulene I carried out was essentially a [6 + 4] cycloaddition with 6-(N,N-dimethylamino)fulvene and butadiene sulfone. The butadiene was prepared in situ from 3,4-dibromotetrahydrothiophene dioxide by sodium methoxide in the same pot as the fulvene.

The fulvene was prepared from cyclopentadiene and dimethylformamide diethyl acetal.

Im pretty sure that dicyclopentadiene dimerized during the fulvene synthesis and though its not as apparent in the NMR (probably because its present in such a small amount), it is extremely obvious in my azulene NMR. We made a few grams of the fulvene vs ~170mg of azulene, to put things into perspective.

Anyway, one of the peaks upfield with the jumble of cyclopentadiene dimerization products in my azulene NMR is incredibly intense. Over 2x higher than any other peak, even from azulene. Its at about 1.4-1.5ppm and appears to be a sharp singlet, i thought maybe some of the pentane I used while running my azulene column may have carried over.. is this feasible? or would the rotovap have taken care of it completely.

There is also a peak just at about 0.7-0.9ppm that I attributed to the methylene bridge in dicyclopentadiene. Its really broad, so im thinking that some of the pentane peaks could be hiding in there also?

[Dan]

Check out this JOC article, mainly pages 2 and 3, it's really handy http://astro.temple.edu/~debrosse/NMRsolvents.pdf

[Fry]

Thanks for that.