Chapter 8 Alkenes and alkynes l Properties and synthesis 8.1 Introduction Alkenes are hydrocarbons whose molecules contain the carbon -carbon double sonde ethylene Hydrocarbons whose molecules contain the cardencicarbonsteiple abond arengalled alkynes.Chapter 8 Alkenes and alkynes I. Properties and synthesis 8.1 Introduction Alkenes are hydrocarbons whose molecules contain the carbon-carbon double bond. Hydrocarbons whose molecules contain the carbon-carbon triple bond are called alkynes. C C H H H H Ethene or ethylene HC CH or acetylene or ethyne