Write resonance structures that account for the stability of the cation of Wurster's salts. Explain why octamethyl- p-phenylenediamine does not form a similarly stable cation radical.

Wurster's salts are organic salts derived from the compound N,N,N',N'-tetramethyl-p-phenylenediamine. The cation of these salts consists of a positively charged nitrogen atom on each side connected by the phenylene group (benzene ring). The structure of this cation can be represented as: \[ [C_6H_4(NMe_2)^+)_2] \] Now, let's analyze its resonance structures to understand its stability.

In order to account for the stability of the cation of Wurster's salts, we consider different resonance structures. Each nitrogen atom can donate a pair of electrons to the benzene ring, creating three double bonds and a positive charge on the nitrogen. \[ (\overset{+}{N} \text{Me}_2 - C_6H_4 - N \text{Me}_2) \equiv [C_6H_4(NMe_2)^+]_2 \] This process can also be represented by resonance arrows: \[ \overset{+}{N}\leftrightarrow C \leftrightarrow C \leftrightarrow C \leftrightarrow N \] These resonance structures show the delocalization of the positive charge over the entire benzene ring, enhancing the cation's stability.

Octamethyl- p-phenylenediamine is a compound that consists of benzene ring with two nitrogen atoms bonded to four methyl groups. The structure can be represented as: \[ C_6H_4(NMe_4)_2 \] We will now explore why it does not form a similarly stable cation radical.

In octamethyl- p-phenylenediamine, all four hydrogen atoms are replaced by methyl groups making it unlikely for the nitrogen to form a cation because it no longer has any available lone pairs to delocalize into the benzene ring. The nitrogen cannot donate a pair of electrons to the benzene ring like in the case of Wurster's salts. Thus, the compound does not form a radical cation similar to Wurster's salts. In conclusion, Wurster's salts have resonance structures that account for the stability of their cation radicals due to the delocalization of the positive charge across the benzene ring. Octamethyl- p-phenylenediamine, however, does not form a similarly stable cation radical due to the lack of delocalization of nitrogen's electron pair into the benzene ring.