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Magazine Chapter 20: Q19P (page 1038)
Explain why each compound is aromatic, antiaromatic, or nonaromatic
a. Isoxazole
b. 1,3-thiazole
c. Pyran
d. Pyrylium ion
e. pyrone
f. 1,2-Dihydropyridine
g. Cytosine
(h)
Short Answer
(a)
Isoxazole
(Aromatic)
b.
1,3-thiazole
(Aromatic)
c.
Pyran
(Nonaromatic)
(d)
Pyrylium ion
(Aromatic)
e.
Pyrone
(Aromatic)
f.
1,2-Dihydropyridine
(Nonaromatic)
g.
Cytosine
(Aromatic)
h.
Antiaromatic
Step by step solution
Aromatic, antiaromatic or nonaromatic
Aromatic: A molecule must be cyclic, planar, completely conjugated, and must satisfy Huckel鈥檚 rule (4n+2 pi electrons) and contains a particular number of pi electrons.
Antiaromatic: A cyclic, planar, completely conjugated compound with 4n pi electrons.
Nonaromatic: A compound that lacks (one or more) of the four requirements to be aromatic.
Classification of given compounds
a. Isoxazole is an aromatic compound because it has4 pielectrons, and one of the lone pairs of oxygen participates in an aromatic sextet. So, it obeys Huckel鈥檚 rule.
Isoxazole
(Aromatic)
b. 1,3-thiazole is an aromatic compound because it has 4 pi-electrons and one of the lone pairs of sulfur participates in the aromatic sextet. So, it obeys Huckel鈥檚 rule.
1,3-thiazole
(Aromatic)
c. Pyran is a nonaromatic compound because it has no conjugated pi-electron system. So, it does not obey Huckel鈥檚 rule.
Pyran
(Nonaromatic)
d. Pyrylium ion is an aromatic compound because it has 4pi-electrons and one of the lone pairs of oxygen participates in an aromatic sextet. Here, the carbocation also undergoes resonance. So, it obeys Huckel鈥檚 rule.
Pyrylium ion
(Aromatic)
e. Pyrone is an aromatic compound because it has 4-pi electrons and one of the lone pairs of oxygen participates in forming an aromatic sextet. So, it obeys Huckel鈥檚 rule.
Pyrone
(Aromatic)
f. 1,2-Dihydropyridine is a nonaromatic compound because it has no conjugated pi electron system and it contains one sp3 hybridized carbon atom. So, it does not obey Huckel鈥檚 rule.
1,2-Dihydropyridine
(Nonaromatic)
g. Cytosine is aromatic because it has 4pi- electrons and one lone pair of nitrogen participates in the formation of an aromatic sextet. So, it obeys Huckel鈥檚 rule.
Cytosine
(Aromatic)
h. The given compound is antiaromatic as it contains 8pi-electrons through the 4n pi-electron rule.
Antiaromatic
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