PP 36: Alkenes
Alkenes:
• Hydrocarbons with at least one double bond
• Each double bond reduces the number of hydrogens in the hydrocarbon by two
• All alkenes are unsaturated hydrocarbons
• Unsaturated Hydrocarbons: Contain less than the maximum number of hydrogens
Alkene example:
1
2
3
4
Naming Alkenes:
1. Identify longest chain containing the double bond. (But-)
2. Number the chain such that the double bond is between the lowest numbers possible
3. The double bond will always fall between two numbered carbons (2-but-)
4. Apply the lower of those two numbers to the double bond & make ending -ene (2-butene)
5.
Problems: (2 posible shapes)
a.
Geometric isomers:
i. Isomers whose arrangement is same side (cis) or opposite side (trans)
of a stationary bond
ii. If the two ends of the chain are on the same side of the line, it is a cis-double bond
iii. If the two ends of the chain are on opposite sides of the line, it is a trans-double bond
b. Apply the cis or trans before the name with a dash (trans - 2 – butane)
Drill: Draw the following: trans-4 - ethyl - 3,6 - dimethyl-5-cyclopentyl – 3 -octene
Draw the named compound or name the drawn compound:

cis-3-ethyl-4,6-dimethyl-5-cyclopropyl-2-octene
Test Review:
Name each of the drawn compounds & draw each of the named compounds:
•
•
trans – 1 – cyclobutyl – 2 – methyl – 3 - hexene
cis – 2 – methyl – 1 - octylcyclohexene
Draw & Name isomers of: C5H10