In the previous article we introduced ortho- ,para- and meta- directors in electrophilic fragrant substitution. Vault to that we covered the system of electrophilic fragrant substitution, and also showed the the mechanism proceeds with a carbocation intermediate.

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Today, we’re going to tie those two principles together, and try to present that whether a substituent is an ortho-, para- or meta- director counts on how the substituent influence the stability of the carbocation intermediate. 

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Clearly, the carbocation v an surrounding oxygen bearing a lone pair is far more stable than a carbocation surrounding to an electron-withdrawing team like CF3.

And the comprises the difference between an ortho-, para- director prefer OCH3 and a meta- director choose CF3.

It’s precious noting that most alkyl teams (such as CH3 ) lack a lone pair, yet are tho ortho-, para- directors. This is regular with whatever we’ve learned before around how alkyl teams are typically stabilizing for carbocations- recall the carbocation stability typically increases through substitution

This pipeline us with the rather tricky instance of halogens.

Why space fluorine, chlorine, bromine, and iodine ortho-, para- directors even though they are deactivating groups?

The answer must come as no surprised if you’ve been complying with along, but we’re walk to leaving this till the following post, due to the fact that this one is long enough already.

Next post: Why room halogens ortho-, para- directors?

Notes

Note 1. It’s more correct to say the ortho- and para- products dominate because the transition states leading to these assets are lower in energy, quite than the energies that the intermediates themselves. After all, it’s the energy of the change states which identify the activation barrier, and also therefore the reaction rate.

See more: Convert 81 Inches Equals How Many Feet Conversion, Convert 81 Inches To Feet

Note 2. Or hyperconjugation, which most textbooks (with the notable exception of Maitland Jones) generally avoid.