So here, based on what we've learned about the reactivity of the alkene, let's answer the following question. Here it says to rank the following alkenes in order of increasing reactivity towards the Heck reaction. So, what we have to do here is to identify what kind of groups are attached to our alkene carbons. So we have here a CN group, an NH₂ group. Here we just have methyl groups, and here, we have a CF₃ group. Here, we also have methyl groups as carbon groups as well.

Now remember, we say that the alkene's reactivity towards the Heck reaction is enhanced if it has electron-withdrawing groups attached to it. So, we need to identify if we have any electron-withdrawing groups attached to my alkene carbons. If we look, we see that CN is an electron-withdrawing group. We also see that CF₃ is an electron-withdrawing group. For C, all we have are methyl groups, which are weak electron-donating groups. And then in B, we have an NH₂ group. Remember, nitrogen here has a lone pair. Because of that lone pair, NH₂ is considered to be a strong electron-donating group. So here we have a strong electron-donating group, and here we have weak electron-donating groups.

So we want to go in order of increasing reactivity, so least reactive to most reactive. The least reactive would have to be B because that one is a strong electron-donating group. So if strong electron-withdrawing groups increase the reactivity of the alkene, then putting a strong electron-donating group would have the opposite effect; it would decrease the reactivity of that alkene towards the Heck reaction. So B would be last. Then we have C, which is electron-donating but weaker.

Then we have CN versus CF₃. In terms of our scale, we can see that CN is a weaker or more moderate electron-withdrawing group compared to CF₃, which is represented here by CF₃. So then we'd say A. So D would be the most reactive alkene towards the Heck reaction because it has the strongest electron-withdrawing group attached to it, CF ₃. So just remember, when it comes to the Heck reaction, we can more greatly increase the reactivity of the alkene towards the Heck reaction if we attach electron-withdrawing groups to it or if we keep it as just a simple ethylene molecule.