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General Organic Chemistry I: Electronic Effects
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Applications: stability of carbocations, carbanions, free radicals
JEE Advanced level
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Difficulty 3 of 3
g1205
Which of the following species, assumed planar and fully conjugated, are antiaromatic?
A
cycloprop-2-en-1-ide (cyclopropenyl anion)
B
cyclohepta-2,4,6-trien-1-ylium (tropylium cation)
C
cyclopenta-2,4-dien-1-ide (cyclopentadienyl anion)
D
cyclopenta-2,4-dien-1-ylium (cyclopentadienyl cation)
Answer: A, D
Antiaromatic species are cyclic, planar and conjugated with 4n pi electrons. The cyclopentadienyl cation has 4 and the cyclopropenyl anion has 4. The tropylium cation and cyclopentadienyl anion have 6 pi electrons each and are aromatic.
Practice General Organic Chemistry I: Electronic Effects
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