Orgo question about acyl halides

[mik30102]

Hello everyone, I am a little confused as to why acyl chlorides are the most reactive with substitution reactions according to my EK book. It says that "Acid chlorides are the most reactive of the carboxylic acid derivatives due to the stability of the Cl- leaving group". I was under the impression that bromine/iodine were better leaving groups then chlorine due to their greater area to spread out the negative charge as the group leaves. Wouldn't this mean a acyl iodide would have the best leaving group? Where is my reasoning flawed? Thank you.

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[LoLCareerGoals]

They aren't as el-neg though. But I think the comparison was more about halides vs all others (anhydrydes down to esters etc).

 

[NontradCA]

They're saying it's more reactive than the anion OH. OH is a strong nucleophile and needs to be protonated before leaving- making it a very poor leaving group, as for the halides It will be I > Br > Cl as you suspected.