Unsaturated Hydrocarbons

Alkenes - hydrocarbons with carbon- carbon double bonds Alkynes - hydrocarbons with carbon- carbon triple bonds

Alkenes Alkenes - one carbon-carbon double bond Alkadienes – two carbon-carbon double bonds Alkatrienes – three carbon-carbon double bonds

Nomenclature of Alkenes 1. Find the longest continuous chain of carbon atoms that contains the double bonds and name it using the ending –ene, -diene or –triene. 2. Number the chain so that the double bond has the lowest possible number. 3. Name, number and alphabetize the constituent groups

4. If cis-trans isomers exist, place the correct term in front of the number of the bond to which it applies. Cis- same side Trans – opposite side NOTE: Double bonds in rings usually exist in the cis form. (Larger rings of eight or more carbons can accommodate the trans form)

Nomenclature examples 1. 2. 3.

4. 5. 6.

Some common names Ethene  ethylene Propene  propylene Vinyl group (derived from ethylene) Allyl group (derived from propylene)

Orbital Model of a Double Bond In a double bond, carbon can only combine with 3 other atoms. Orbitals are arranged like an equilateral triangle. The bond angle is 120° TRIGONAL Carbon-carbon double bonds have restricted rotation. Geometric isomers occur when the groups attached to each carbon are different from each other.

Name each of the following and indicate if they are geometric isomers or not.