Question

Would you expect a conjugated diyne such as 1,3-butadiyne to undergo Diels-Alder reaction with a dienophile? Explain.

Short answer

Because of the strain that will be caused in the cyclic transition state

Step-by-step solution

Diels-Alder reaction

Diels-Alder reaction was discovered by the German chemists Otto Diels and Kurt-Alder in 1928. Diels-Alder reaction is an important organic reaction which includes a substituted alkene in the form of a dienophile and a conjugated diene. It proceeds via concerted mechanism. Diels alder reaction can be used to generate 6 membered rings since there is a simultaneous construction of two new Carbon-carbon bonds.

Or

Diels-Alder reaction is a pericyclic reaction. It is a reaction between a conjugated diene ( two double bonds) and a dienophile( a substituted alkene with electron withdrawing group). The reaction is stereospecific i.e., the cis dienophile will give cis stereochemistry in product and trans dienophile will generate product with cis stereochemistry.

Diene and dienophile

Diene is an organic compound which comprises of two conjugated pi bonds (4 pi bonds) while dienophile is a diene loving compound containing 2 pi electrons. When the interaction between them, occurs a transition state without any additional energy barrier, is obtained.

Explanation

$\mathrm{HC}\equiv \mathrm{CC}\equiv \mathrm{CH}$(1,3-butadiyne) can not be used as a diene in Diels-Alder reaction since, it is linear so that end carbons are not able to interact with the dienophile in cyclic transition state. Moreover, in the products formed there will be high strain because of the presence of two sp hybridized carbons present in a six membered ring.