why are acyl chlorides less reactive when attached to a benzene ring?

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JacobAlevels
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why are acyl chlorides less reactive when attached to a benzene ring rather than a hydrocarbon chain? i don't understand what chemguide means to say by this:
Remember that acyl chlorides are especially reactive because of the fair amount of positive charge on the carbon with the oxygen and chlorine attached. If the -COCl group is attached to a benzene ring, that charge can get spread around the whole benzene ring by delocalisation. If it is more spread out, it is going to be less attractive to nucleophiles.
okay so most of the reactions of acyl chlorides are nucelophilic substitutions, and that requires C to be C+. how does the PLUS charge spread around the benzene ring by delocalisation? isn't it only the NEGATIVE charge that spreads when orbitals overlap? how come the PLUS charge is spreading around the benzene ring?
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(Original post by JacobAlevels)
why are acyl chlorides less reactive when attached to a benzene ring rather than a hydrocarbon chain? i don't understand what chemguide means to say by this:
Remember that acyl chlorides are especially reactive because of the fair amount of positive charge on the carbon with the oxygen and chlorine attached. If the -COCl group is attached to a benzene ring, that charge can get spread around the whole benzene ring by delocalisation. If it is more spread out, it is going to be less attractive to nucleophiles.
okay so most of the reactions of acyl chlorides are nucelophilic substitutions, and that requires C to be C+. how does the PLUS charge spread around the benzene ring by delocalisation? isn't it only the NEGATIVE charge that spreads when orbitals overlap? how come the PLUS charge is spreading around the benzene ring?
No, if you have a delocalised pi system then the overall number of electrons (charge) are spread out over the total number of nuclear centres. This can 'spread out' a positive charge.
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