If a system has 6 π electrons, what is n in the 4n+2 rule?

If a system has 6 π electrons, what is n in the 4n+2 rule?

• A. 1
• B. 0
• C. 2
• D. 3

Answer: (A)

Hückel's rule states that a planar cyclic conjugated system is aromatic when it contains 4n + 2 π electrons, where n is a nonnegative integer. For a system with 6 π electrons, set 6 = 4n + 2. Subtracting 2 gives 4n = 4, and dividing by 4 yields n = 1. This value satisfies the rule, since 6 = 4(1) + 2. If n were 0 or 2, the number of π electrons would be 2 or 10, not 6. So, the value is 1.

Hückel's rule states that a planar cyclic conjugated system is aromatic when it contains 4n + 2 π electrons, where n is a nonnegative integer. For a system with 6 π electrons, set 6 = 4n + 2. Subtracting 2 gives 4n = 4, and dividing by 4 yields n = 1. This value satisfies the rule, since 6 = 4(1) + 2. If n were 0 or 2, the number of π electrons would be 2 or 10, not 6. So, the value is 1.