Aromatic compounds &
Their Reactions

What are aromatic compounds?

Cyclic organic compounds which have delocalized $\pi$ electrons and therefore increased stability.

What is Hückel's rule?

Hückel's rule determines the number of $\pi$ electrons in aromatic, planar monocylic rings:

(4n + 2) $\pi$ electrons, where n = is 0, 1, 2, 3, 4É

Therefore, planar monocyclic rings with 2, 6, 10, and 14 delocalized ¹ electrons will be aromatic. Further, carbons of aromatic rings are $sp^{2}$ hybridized carbons.

What aromatic ring has 6 $\pi$ electrons?

Figure 46.1: Benzene.

What are some common benzene derivatives?

Figure 46.2: Common benzene derivatives: Fluorobenzene (a), toluene (b), phenol (c) and benzoic acid (d).

Figure 46.3: Methyl phenyl ketone (left) and benzyl bromide (right).

How are the relative positions of substituents on benzene rings identified?

Figure 46.4: Relative positions of substituents on benzene rings.

What are the effects of substituent positioning on the benzene ring?

Table 46.1: Activating electron-donating groups for benzene substituent groups.

Ortho-Para Directors	Meta Directors
Strongly activating	Strongly activating
(e$^{-}$ donating)	(e$^{-}$ donating)
$-NH_{2}$
$-NR_{2}$
$-OH$
$NHCOR$	$N/A$
$-OCOR$
$-OR$
$-R$

Table 46.2: Deactivating electron-withdrawing groups for benzene substituent groups.

Ortho-Para Directors	Meta Directors
Deactivating	Deactivating
(e$^{-}$ withdrawing)	(e$^{-}$ withdrawing)
$-F, \ -Cl, \ - Br, \ -I$	$-NO_{2}$
	$-SO_{3}$H
	Carbonyls47.1