Chapter 14, Problem 14.1P

Interpretation Introduction

(a)

Interpretation:

The model of cyclohexyne is to be built. An explanation for the instability of cyclohexyne structure is to be stated.

Concept introduction:

Alkynes are hydrocarbons containing at least one carbon-carbon triple bond. The triple bonded carbons are sp hybridized. Alkynes due to triple bonds do not rotate and have linear geometry with bond angle $180°$.

Answer to Problem 14.1P

The model of cyclohexyne is shown below.

Cyclohexyne is unstable because of the ring strain due to the reduced bond angle in six carbon cyclic structure.

Explanation of Solution

Alkynes are hydrocarbons containing at least one carbon-carbon triple bond. The triple bonded carbons are sp hybridized. Alkynes have a linear geometry with bond angle of $180°$. Cyclohexyne is a cyclic compound of six carbon atoms and contains one triple bond. The structure of cyclohexyne is shown below.

Figure 1

In cyclohexyne, the six carbon atoms ring contains one carbon-carbon triple bond. The bond angle from $180°$ is reduced to nearly $60°$. Thus, the six-membered ring experiences ring strain due to small bond angle and the ring becomes unstable. Therefore, cyclohexyne is unstable.

Conclusion

Cycloalkynes with carbon ring less than $8$ carbons is unstable due to large bond angle strain.

Interpretation Introduction

(b)

Interpretation:

The structure of cyclodecyne is to be built. The stability of cyclodecyne and cyclohexyne is to be compared.

Concept introduction:

Alkynes are hydrocarbons containing at least one carbon-carbon triple bond. The triple bonded carbons are sp hybridized. Alkynes due to triple bonds do not rotate and have linear geometry with bond angle $180°$. The cycloalkynes which are smaller than cyclooctynes are unstable.

Answer to Problem 14.1P

The model of cyclodecyne is shown below.

Cyclodecyne is more stable than cyclohexyne due to less bond angle strain.

Explanation of Solution

Alkynes are hydrocarbons containing at least one carbon-carbon triple bond. The triple bonded carbons are sp hybridized. Alkynes have a linear geometry with bond angle of $180°$. Cyclodecyne consist of a cyclic ring of ten carbon atoms and contains one triple bond. The structure of cyclodecyne is shown below.

Figure 2

Cyclodecyne is comparatively stable than cyclohexyne because of the reduced ring strain. In cyclodecyne, the ten membered carbon ring of is large enough to accommodate a triple bond due to its floppiness arised by carbon-carbon bond rotations.

In cyclohexyne, the six carbon atoms ring contains one carbon-carbon triple bond. The bond angle from $180°$ is reduced nearly to $60°$. Thus, the six-membered ring experiences ring strain due to small bond angle and the ring becomes more unstable. Therefore, cyclodecyne is comparatively stable than cyclohexyne because of the reduced ring strain

Conclusion

The structure of cyclodecyne is shown in Figure 2.

Cyclodecyne is more stable than cyclohexyne due to less bond angle strain and large ring size of cyclodecyne.