# Regioselectivity in Diels–Alder reaction between 2-nitrobuta-1,3-diene and acrylonitrile

Since $$\ce{-CN}$$ shows strong −I effect, there will be δ+ charge on the carbon adjacent to it. Similarly, $$\ce{-NO2}$$ shows strong −I and –M effects. So, I proposed that π-electrons are being donated to the electron-deficient parts:

But the answer given in my book has $$\ce{-CN}$$ group at the third position to $$\ce{-NO2}$$ group. Can someone please tell me where I have got my concepts wrong?

• Regardless of any simple electronic models, since DA part of what we call frontier orbital chemistry it should be dependend on orbital coefficients. There are tables for dienes and dienophiles and if I simply connect the sides with the biggest coefficients of the same symmetry I end up with your solution. Source: 10.1021/ja00793a069 – Justanotherchemist Nov 8 '18 at 9:52
• Not convinced by this DA reaction; both dienophile and diene are very electron-deficient... – orthocresol Dec 9 '18 at 11:12

You pointed out correctly that $$-CN$$ has a great $$-I$$ effect but it won't bring a $$+\delta$$ on adjacent carbon atom, reason being it's instability. Apply electromeric effects on propanenitrile.