Why are aromatic compounds so stable?

Question

I've never actually been told deeper reasons for this. In organic chemistry classes (1 and 2) we're usually told that aromatic compounds are very stable whereas anti-aromatic ones are not, and also, we're taught how to identify them. Why are they, though? (I'm pretty sure this has something to do with the de-localisation of electron pairs, which enhances stability, but I only have a vague idea. Is that the only reason?)

Answer 1

First, aromatic compounds have 2, 6, 10, 14... electrons in their conjugated system, and if you recall, these are the "stable octect" numbers corresponding to fully-filled s, p, d, f subshells. But yes, the great stability of aromatic compounds is indeed due to their delocalization of pi electrons (resonance stability). What this really means for aromatic compounds [or any compounds that display resonance] is that pi electrons (double bonds or lone pairs) are never in one place for too long; they are constantly moving (like in the benzene ring or even a sulfate ion), and when they are constantly moving, they become less vulnerable to reactions (addition reactions, electrophilic substitution, etc.), and therefore the compound as a whole is less reactive thus more stable.

Answer 2

It's not that anti-aromatic compounds are unstable, they're just much less stable in relation to aromatic compounds. You're right though, it's primarily due to the delocalization of electron pairs.