eli5: why does a nucleophile ALWAYS attack an electrophile?

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Learning reaction mechanisms, and I have been told ‘nucleophiles always attack the electrophiles’, but I don’t understand why. Why not the other way around? Is it to do with Molecular orbital theory, HOMO, and LUMO? Can someone please dumb it down and explain it like I am 5 months old.

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I think you’re overcomplicating this and reading too much into it being called “attack”.

When the “nucleophile attacks an electrophile”, it’s like saying “this magnet’s north pole attacks the other magnet’s south pole”. Nucleophiles and electrophiles are just regions of relatively-positive and relatively-negative charge that are drawn to react with each other. It’s not literally one “attacking” the other. You could say it IS the other way around, with “electrophiles attacking nucleophiles” and the products you get would be the same.

It’s just a convention, due to the way the arrowheads in the mechanisms are pointing, to describe it like one molecule is doing the action and “attacking” the other. But it’s actually a lot more like two magnets coming together. You could say the north poles attract south poles, or that south poles attract north poles, and it’s all the same thing.