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Exercise: addition of HX to alkynes - mechanism

Exercise

Why is an intermediate carbenium ion in the HX addition to alkynes unlikely?

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correct

wrong

partly correct

This is the right answer

Because of the stability of the vinyl cation

No, sorry

Because of the instability of the vinyl anion

Sorry, that is wrong

Because of the instability of the vinyl cation

Correct!

Because of the stability of the vinyl anion

Sorry, that is wrong

Because of the instability of the vinyl zwitterion

No, sorry

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Exercise

Which alternative mechanism of the HX addition to alkynes has been proposed?

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wrong

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A mechanism with an acyclic transition state, analogous to the bromination of alkenes

Sorry, that is wrong

A mechanism with an cyclic intermediate, analogous to the elimination of bromine from dibromoalkenes

No, sorry

A mechanism with an acyclic transition state, analogous to the bromination of alkynes

Sorry, that is wrong

A mechanism with an cyclic intermediate, analogous to the bromination of alkenes

That is correct!

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Exercise

The proposed mechanism also explains the preference of ...

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... cis addition

Sorry, that is wrong

... trans substitution

No, sorry

... syn substitution

Sorry, that is wrong

... anti addition

That is correct!

... anti elimination

No, sorry

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Exercise

The resonance structures of the cyclic intermediate show ...

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... the distribution of the positive charge to the hydrogen and the two alkyne carbon atoms involved

Correct

... the distribution of the negative charge to the hydrogen and the two alkyne carbon atoms involved

Sorry, that is wrong

... the distribution of the positive charge to the hydrogen and the three alkyne carbon atoms involved

No, sorry

... the distribution of the negative charge to the hydrogen and the three alkyne carbon atoms involved

Sorry, that is wrong

... the distribution of the negative charge to the two hydrogen and the three alkyne carbon atoms involved

No, sorry

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Exercise

Fig.1

What does the illustration show?

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This is the right answer

Anti-Markovnikov orientation in the HX addition to terminal alkynes

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Markovnikov orientation in the HX addition to terminal alkynes

That is correct!

Markovnikov orientation in the HX elimination from terminal alkynes

No, sorry

Anti-Markovnikov orientation in the HX elimination from terminal alkynes

Sorry, that is wrong

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