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20.5 Identifying if aromatic, antiaromatic, or nonaromatic

Link to the video: Aromatic and antiaromatic compounds
Aromatic and antiaromatic compounds

20.5 Identifying if aromatic, antiaromatic, or nonaromatic

4N+2, Hückel’s rule

Aromatic systems are cyclic, completely conjugated systems that are more stable than their open-ring counterparts. Antiaromatic systems are cyclic, completely conjugated systems that are less stable than their open-ring counterparts. In order for a system to be aromatic or antiaromatic, it MUST have the following characteristics.

1. It must be a cyclic compound. If it is not a ring, it is neither aromatic nor antiaromatic. 2. It must be completely conjugated at every atom in the ring. Each atom of the ring must have an unhybridized p-orbital that can overlap. 3. The ring must be a flat, planar structure. All of the p-orbitals must be able to overlap with each other so the pi-electrons can be shared.

If any of the three above considerations is not true for a compound, then the compound is a nonaromatic system.

3. Each of the following compounds is nonaromatic. Which of the previous rules, 1-3, does each compound break?

a)
Problem 3a, how to tell if a ring is aromatic
b)
Problem 3b, how to tell if a ring is aromatic
c)
Problem 3c, how to tell if a ring is aromatic

3. Each of the following compounds is nonaromatic. Which of the previous rules, 1-3, does each compound break?

Problem 3, how to tell if a ring is aromatic, answer

4. For the following compounds, determine whether the molecule is aromatic, antiaromatic, or nonaromatic. Assume the molecules are planer.

a)
Problem 4a, how to tell if a ring is aromatic
b)
Problem 4b, how to tell if a ring is aromatic
c)
Problem 4c, how to tell if a ring is aromatic
d)
Problem 4d, how to tell if a ring is aromatic
e)
Problem 4e, how to tell if a ring is aromatic
f)
Problem 4f, how to tell if a ring is aromatic
g)
Problem 4g, how to tell if a ring is aromatic
h)
Problem 4h, how to tell if a ring is aromatic
i)
Problem 4i, how to tell if a ring is aromatic

4. a) aromatic b) antiaromatic c) antiaromatic d) nonaromatic e) aromatic f) aromatic g) antiaromatic h) nonaromatic i) antiaromatic

5. Predict whether the following compounds would be flat (planar) or not.

a)
Problem 5a, how to tell if a ring is aromatic
b)
Problem 5b, how to tell if a ring is aromatic
c)
Problem 5c, how to tell if a ring is aromatic
d)
Problem 5d, how to tell if a ring is aromatic
e)
Problem 5e, how to tell if a ring is aromatic

5. a) no b) no (a and b would be antiaromatic if flat) c) yes d) yes e) yes (c, d, and e would be aromatic if flat.)