MolSynapsequestion bank

MolSynapse / Question bank / General Organic Chemistry I: Electronic Effects / Resonance: rules, conditions and drawing resonating structures

JEE Advanced levelSingle correct optionDifficulty 3 of 3g1048

Which of the following is the most unstable (antiaromatic) species?

Acyclopenta-2,4-dien-1-ide (cyclopentadienyl anion)
Bcycloprop-2-en-1-ylium (cyclopropenyl cation)
Ccyclohepta-2,4,6-trien-1-ylium (tropylium cation)
Dcyclopenta-2,4-dien-1-ylium (cyclopentadienyl cation)

Answer: D

Count pi electrons in each planar cyclic conjugated ring. The cyclopentadienyl cation has 4 pi electrons (4n), so it is antiaromatic. The anion has 6, the tropylium cation 6 and the cyclopropenyl cation 2, which are all (4n+2) and aromatic.

Practice General Organic Chemistry I: Electronic Effects More on Resonance: rules, conditions and drawing resonating structures

Previous questionNext question

More questions on Resonance: rules, conditions and drawing resonating structures

Count the distinct resonance structures of the phenoxide ion C6H5O^-, counting each different Kekule arrangement separately: the negative ch... JEE Advanced level
The pKa of 4-nitrophenol is about 7.2, whereas that of 3,5-dimethyl-4-nitrophenol is about 8.3. The best explanation is that in the dimethyl... JEE Advanced level
Which compound has the least extent of delocalisation of the nitrogen lone pair into the benzene ring? JEE Advanced level
Which hydrocarbon is the most acidic? JEE Advanced level
Acetamide, CH3CONH2, is protonated on oxygen rather than on nitrogen because JEE Advanced level
In methyl vinyl ether, CH2=CH-OCH3, the terminal CH2 carbon is the most electron-rich carbon because JEE Advanced level