Question

At what position will electrophilic aromatic substitution occur for the following compounds? Which is the most reactive and least reactive?

bromobenzene
nitrobenzene
benzoic acid
toluene
phenol
benzaldehyde

Answer 1

See the explanation below.

Explanation:

The table below shows the effect of substituents on both the rate and orientation of electrophilic aromatic substitution reactions.

`color(white)(ll)bb"Group"color(white)(mmmmml)bb "Effect" color(white)(mmmmmmmmll)bb"Direction"`
`stackrelcolor(blue)(——————————————————————————)(color(white)(m)"-OH"color(white)(mmll) "Strongly activating EDG"color(white)(mmmll) "ortho, para")`
`color(white)(m)"-CH"_3color(white)(mml) "Moderately activating EDG"color(white)(mml) "ortho, para"`
`color(white)(m)"-Br" color(white)(mmml)"Weakly deactivating EDG"color(white)(mmll) "ortho, para"`
`color(white)(m)"-CHO" color(white)(mm)"Moderately deactivating EWG"color(white)(mm) "meta"`
`color(white)(m)"-COOH" color(white)(m)"Deactivating EWG"color(white)(mmmmmmmm) "meta"`
`color(white)(m)"-NO"_2 color(white)(mml)"Strongly deactivating EWG"color(white)(mmmll) "meta"`

The effects are a combination of resonance and inductive effects.

Electron donating groups (EDGs) increase the rate and direct ortho, para.

Most EDGs have lone pairs on the atom attached to the ring.

Electron withdrawing groups (EWGs) decrease the rate and direct meta.

EWGs have a double or triple bond or a partial or formal positive charge on the atom attached to the ring.
`color(white)(l)`

Phenol is most reactive, and nitrobenzene is least reactive.

In a bromination reaction, the products are:

`"phenol" →color(white)(mmmll) o"- and"color(white)(l)p"-bromophenol"`

`"toluene" →color(white)(mmml) o"- and"color(white)(l) p"-bromotoluene"`

`"bromobenzene" → o"- and"color(white)(l) p"-dibromobenzene"`

`"benzaldehyde" →color(white)(l) m"-bromobenzaldehyde"`

`"benzoic acid" →color(white)(lll) m"-bromobenzoic acid"`

`"nitrobenzene" →color(white)(ll) m"-bromonitrobenzene"`