2.3 NAMING ALKENES ….. the ending of the name is the thing ….. it indicates the type of compound ….. alkenes end in “ene”

ALKENES ( -ENE ) C H C H C H C H C H C H H C Count carbon atoms in the longest chain that contains the C=C Change the ending (suffix) from -ane to -ene Number the chain from the end closest to the C=C Assign a locant number for the C=C. 1 2 3 4 5 6 C H C H C H C H C H C H 3 2 2 3 2- hexene 1 2 3 4 5 H C 3 4-methyl- 2-pentene Place the number and name of substituents in front of the alkene name In numbering, the double bond takes precedence over substituents.

Naming Dienes C H C H C H C H C H C C H C H C H H C H C Count carbon atoms in the longest chain that contains both C=C Change the ending (suffix) from -ane to -diene Number the chain from the end closest to the C=C Assign a locant number for each C=C. 1 2 3 4 5 6 C H C H C H C H C H 3 3 2,4- hexadiene 1 2 3 4 5 C C H C H C H H C 3 2 H C 3 4-methyl- 1,3- pentadiene Place the number and name of substituents in front of the alkene name In numbering, the double bond takes precedence over substituents.

Namining cycloalkenes 3 1 2 4 5 6 C H 2 3 3-ethyl- 1- cyclohexene ( 3-ethylcyclohexene ) Use cyclo prefix for the root name of cylic alkenes Number the ring so the C=C are carbons 1 & 2 and the attached groups have the lowest numbers

Namining cycloalkadienes 3 1 2 4 5 6 C H 2 3 5-ethyl- 1,3- cyclohexadiene Use cyclo prefix for the root name of cylcoalkenes and change the ending to diene Number the ring so the C=C have the lowest numbers and the attached groups have the lowest numbers

Summary ALKENE IUPAC NOMENCLATUE Count the carbons in the longest chain containing the C=C and number them from the end closest to the C=C. Name is chain length, root name + “ene” preceded by a prefix number indicating the position of the C=C. (1-butene) Attached groups are named alphabetically, preceded by a number that signifies the carbon they are attached to. Use Greek prefixes (di, tri, tetra, etc) to indicate the number of same attached groups if there are more than one. Use cis / trans in front of the name to indicate geometric isomers if needed (different groups on C=C)

PRECEDENCE 1. In numbering, functional groups take precedence over substituents. Since functional groups are indicated by changing the ending, and substituents are indicated by prefix, the following rule applies: ANYTHING NAMED IN THE ENDING HAS NUMBERING PRECEDENCE OVER ANYTHING NAMED IN THE PREFIX 2.There is also an order of precedence for functional groups named in the endings. Functional groups of higher precedence are named last in the ending.