1. For each of the species below, identify any cyclic conjugated system, then A.

Question

1.

For each of the species below, identify any cyclic conjugated system, then A. Determine the number of electrons in a system of cyclic conjugation (zero if no cyclic conjugation). B. Specify whether the species is aro aa anti-aromatic, or nal non-aromatic neither matic. aromatic nor anti-aromatic). (Presume rings to be planar unless structure obviously prevents planarity. Ifthere is more than one conjugated ring, count electrons in the largest.) A. Electrons in a cyclic conjugated system B.The compound is (a, aa, or na) A. Electrons in a cyclic conjugated system B.The compound is (a, aa, or na)

Explanation / Answer

A molecule is aromatic when it has number of electrons according to Huckel rule; 4n+ 2, where n is a natural number (0, 1, 2, 3…)

When, n = 0, we get (4 × 0 + 2) = 2, n = 1, we get (4 × 1 + 2) = 6, n = 2, we get (4 × 2 + 2) = 10, n = 3, we get (4 × 3 + 2) = 14, n = 4, we get (4 × 4 + 2) = 18

So when the total number of electrons in the ring system equal to 2, 6, 10, 14, 18…..& so on as per the Huckel rule the molecule is aromatic.

A molecule is anti-aromatic when it has number of electrons equals to 4n, where n is a natural number (0, 1, 2, 3…). Solving for 4n gives us numbers like 4, 8, 12, 16…& so on.

Apart from this molecule should be cyclic, conjugated, sp2 hybridized & planar to become aromatic or anti-aromatic.

When the molecule does not follow any of the above parameters it is non-aromatic.

1)

A) Four

B) aa

2)

A) Six

B) a

3)

A) Six

B) a

4)

A) Six

B) na

5)

A) Four

B) aa

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