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Exercise: Stability of radicals 3

Exercise

Which of the following statements are correct?

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Radicals have an unpaired electron.

Radicals are usually instable and highly reactive.

Radicals do not have an electron octet.

Radicals are characterized by a low reactivity and high selectivity.

Because of their high reactivity and their low selectivity, radicals are a threat to biolgical systems.

Radicals are usually very stable.

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Exercise

Comparison of radicals and carbocations. Which of the following statements are correct?

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Like carbocations, radicals usually appear only during intermediate stages.

The stability of radicals can be compared by the dissociation energies of the C-H bonds that must be homolytically cleaved in order to obtain the radicals.

Compared to carbocations, carbon-centered radicals usually exhibit a shorter half-life period.

The stability of radicals - as is the case in carbocations - depends on their structure. Higherly substituted radicals are more stable than lower substituted ones.

Similar to carbocations, radicals usually serve only as inhibitors.

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Exercise

Which sequence of stability do radicals show?

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Allylic, benzylic > primary > secondary > tertiary > methyl.

Allylic, benzylic > secondary > tertiary > primary > methyl.

Allylic, benzylic > tertiary > secondary > primary > methyl.

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Exercise

The sequence of stability of radicals can be explained by different amounts of hyperconjugation. Which of the following statements are correct?

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The more alkyl substituents a radical carbon atom possesses, the less stabilized it is by superconjugation.

The more allyl substituents a radical carbon atom carries, the more stabilized it is by ultraconjugation.

The more alkyl substituents a radical carbon atom has, the less stabilized it is by hyperconjugation.

The more alkyl substituents a radical carbon atom possesses, the more stabilized it is by hyperconjugation.

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Exercise

The interaction of the double-occupied C-H σ bonding orbital with the single-occupied, non-bonding p orbital of the radical carbon atom is comparable to the stabilization by hyperconjuation in carbenium ions. However, what is the important difference?

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In carbenium ions, the stabilization is influenced by the overlapping of a double-occupied C-H bonding orbital with a double-occupied, non-bonding 2p orbital, while in radicals this is caused by the overlapping of a C-H bonding orbital with a single-occupied, non-bonding 2p orbital.

In carbenium ions, the stabilization is the result of the overlapping of a double-occupied C-H bonding orbital with an unoccupied, non-bonding 2p orbital, while in radicals this is caused by the overlapping of a C-H bonding orbital with a single-occupied, non-bonding 2p orbital.

In carbenium ions, the stabilization is influenced by the overlapping of an unoccupied C-H bonding orbital with an unoccupied, non-bonding 2p orbital, while in radicals this is caused by the overlapping of a C-H bonding orbital with a double-occupied, non-bonding 2p orbital.

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Exercise

Which of the following statements are correct?

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The stability of radicals may be increased by aromatic substituents located at the radical carbon atom.

A carbon-centered radical with an immobilized electron is instable at room temperature.

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