Unsaturated Hydrocarbons Contain at least one double or triple bond between carbon atoms.

Alkenes and alkynes Alkenes have at least one double bond. (CnH2n) Alkynes have at least one triple bond. (CnH2n-2)

Procedure for Naming Alkenes and Alkynes Identify and name the longest continuous chain with the maximum number of double or triple bonds. Indicate the presence of a double bond with prefix-ene and a triple bond with –yne. Number the carbon chain so as to give the lowest number to double or triple, (Double bonds take priority over triple bonds if there is a choice.) then groups named by prefixes (alkyl groups, halides)Complete suffix by identifying the location of double or triple bonds.

Common Names Alkenes are referred to as “alkylene”. Ethylene  vinyl (CH2=CH-) Propylene  allyl (CH2=CH-CH2-) Acetylene  simplest alkyne

Isomerisms in Alkenes and Alkynes Geometric Isomers:cis and trans isomers; a type of stereoisomerism in which atoms or groups display orientation differences around a double bond. Cis-trans must have two different groups attacked. Trans is more stable.

Cycloalkanes Same as alkanes but joined into a ring. Conformations are not isomers because they result from twisting around a bond. Boat vs chair Cycloalkenes are rings with double bonds.

Aromatics Benzene is the basic aromatic. (C6H6) They contain one or more benzene rings. Name comes from the Greek aroma. Rather strong often pleasant odor. Ring in a plane. The alternating double bonds are really 6 equivalent bonds. Longer than a double bond but shorter than a single bond.

Common Aromatics Toluene = methylbenzene

xylene Xylene is dimethyl benzene. Prefixes tell you where the groups are located. Ortho – group adjacent to each other. O-xylene

Meta - one carbon between groups. m-xylene

Para- groups are opposite each other Para- groups are opposite each other. This means there are two carbons between the groups.