Cycloalkenes and Cycloalkynes

The C—C=C angle in alkenes normally is about 122°, which is 10° larger than the normal C—C—C angle in cycloalkanes. This means that we would expect about 20° more angle strain in small-ring cycloalkenes than in the cycloalkanes with the same numbers of carbons in the ring. Comparison of the data for cycloalkenes in Table 12-5 and for cycloalkanes in Table 12-3 reveals that this expectation is realized for cyclopropene, but is less conspicuous for cyclobutene and cyclopentene. The reason for this is not clear, but may be connected in part with the C-H bond strengths (see Section 12-4B). 

Cyclopropene has rather exceptional properties compared to the other cycloalkenes. It is quite unstable and the liquid polymerizes spontaneously although slowly, even at —80°. This substance, unlike other alkenes, reacts 

Compound Mp, °C Bp, °C —AH0 of hydrogenation, kcal mole-1 Net strain energy,6 kcal mole-1 

Exercise 12-24 Space-filling models (Section 2-2B) indicate that the chiral forms of frans-cyclopentadecene are likely to be readily interconverted at room temperature. How and where might frans-cyclopentadecene be substituted to give stable chiral forms that possess a chiral center but no chiral carbon atoms  

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We thus have the families cycloalkanes, cycloalkenes, and cycloalkynes, as well as the multi-double and triple-bond variants such as cycloalkadienes and -atrienes, and cycloalkadiynes, -atriynes, etc. Naming the cyclo compounds corresponds to the naming of the straight-chain forms except that carbon atoms are numbered such that substituents are on the lowest numbered carbon atoms. This... 

Other alicyclic hydrocarbons have the same kind of properties as their open-chain counterparts, and they are characterized in the same way cycloalkanes by their general inertness, and cycloalkenes and cycloalkynes by their response to... 

VII. HIGH-SYMMETRY CHIRAL TWISTED -ELECTRON SYSTEMS 1 CYCLOALKENES AND CYCLOALKYNES... 

Cycloalkanes - Saturated monocyclic hydrocarbons (with or without side chains). See alicyclic compounds. Unsaturated monocyclic hydrocarbons having one endocyclic double or one triple bond are called cycloalkenes and cycloalkynes, respectively. [5]... 

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