The directing effect of multiple substituents is dominated by the most powerful activator. Which is the most powerful activator for vanillin

- OH group is the most powerful activator

Explanation:

The most powerful activator for Vanillin is the  - OH group and this is due to the effect of the +R  on the  - OH group and also there is more overlapping experienced in -OH groups compared to - OCH3 group

attached below is the reaction scheme

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