Benzene has a total of six pi electrons, or three electron pairs. With an odd nu

Question

Benzene has a total of six pi electrons, or three electron pairs. With an odd number of electron pairs, benzene is aromatic. In contrast, cyclobutadiene and cyclooctatetraene each have an even number of electron pairs (two pairs and four pairs, respectively) and do not exhibit aromatic stabilization. The requirement for an odd number of electron pairs is called Huckel's rule. Specifically, a compound can only be aromatic if the number of pi electrons in the ring is 2,6, 10,14, 18, and so on. This series of numbers can be expressed mathematically as 4n + 2, where n is a whole number. In the upcoming section, we will use MO theory to explain why aromatic stabilization requires an odd number of electron pairs (4n + 2 electrons). CONCEPTUAL CHECKPOINT Predict whether each of the following compounds should be aromatic: MO Theory and Frost Circles In this section, we will use MO theory to explain the source of Huckel's rule for planar. conjugated ring systems. We already analyzed the MOs of benzene (Figure 18.4) to explain its stability. Let's now turn our attention to the MOs of cyclobutadiene (C_4H_4) and cyclooctatetraene (C_8H_8) to see how MO theory can explain the observed instability of these compounds. We will start with square cyclobutadiene, which is a system constructed from the overlap of four atomic p orbitals (Figure 18.5).

Explanation / Answer

a compound shows aromatic nature when it satisfies the following conditions,

1) Cyclic planar structure

2) Conjugate double bonds

3) it satis fies Huckles rule ( (4n+2) pi electron rule where n = 1, 2, 3, 4........)

From the given (b) compound only satisfies All the above aromatic conditions. So it is aromatic compound.

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