Why is C4H4S (thiophene) aromatic?

Answer 1

Thiophene is aromatic because it has six π electrons in a planar, cyclic, conjugated system.

The structure of thiophene is

At first glance, it appears that thiophene has only four π electrons in a butadiene system, plus an #sp^3# hybridized sulfur atom with two electron pairs.

However, if the sulfur atom re-hybridizes to #sp^2#, it will have an electron pair in a #3p# orbital that can overlap with the carbon #2p# orbitals on either side.

This gives a planar, cyclic, conjugated system that contains six π electrons.

According to Hückel's rule, then, thiophene is an aromatic compound.

The resonance energy of thiophene is 122 kJ/mol.

This is less than the resonance energy of benzene (152 kJ/mol), because the #3p# orbital of #"S"# is bigger than the #2p# orbitals on #"C"#, so the orbital overlap is less effective.

We can see this in a contour plot representing the electron density of thiophene

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Answer 2

C4H4S (thiophene) is aromatic because it satisfies the criteria for aromaticity, which include having a planar, cyclic structure with conjugated pi electrons and following Hückel's rule, which states that the number of pi electrons in the aromatic system must be 4n + 2, where n is a non-negative integer. Thiophene has a planar, cyclic structure with 6 pi electrons, fulfilling Hückel's rule, and its delocalized electron density contributes to its aromaticity.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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