13.1 Properties of alkenes

• Alkenes are unsaturated hydrocarbons that contain at least one double bond between carbon atoms
• Alkenes have the general formula CnH2n
• The carbon-carbon double bond consists of a pi bond and a sigma bond
• The pi bond is the sideways overlap of adjacent p orbitals above and below the bonding carbons
• The pi bond prevents rotation about the double bond
• The sigma bond is the overlap of orbitals directly between the bonding atoms
• There are three regions of electron density around a carbon atom in a carbon-carbon double bond leading to bond angles of 120 degrees
• Alkenes are more reactive than alkanes
• The pi bond introduces a region of high electron density above and below the carbon-carbon double bond
• Electron-deficient species called electrophiles can react with the areas of electron density
• Pi bonds have a smaller bond enthalpy than sigma bonds so are broken more easily