CH 7-2: Alkene & Alkyne Nomenclature Identify longest carbon chain containing the double bond Drop the –ane ending and add –ene Numbering is fixed by location of the double bond Alkene location defined by two carbons; use lowest number to indicate position. 2,4-dimethyl-2-pentene 5 4 3 2 1

Nomenclature: cis/trans Geometry Identify longest carbon chain containing the double bond Drop the –ane ending and add –ene Numbering is fixed by location of the double bond Cis/trans geometry: used when same atom or group is found on each sp2 carbon: trans-(S)- 5-bromo-3-methyl-2-hexene

Nomenclature: E/Z Geometry Can the compound below be designated cis or trans? Alternative to cis/trans is the E/Z nomenclature: used if all four sp2 substituents are different (cis/trans can not be used). Determine highest priority atom at each sp2 carbon. If on same side of double bond use (Z), if on opposite sides of double bond use (E). (Z)- 3-bromo-4-methyl-3-heptene

Alkyne Nomenclature – similar to alkenes Alkane …………Alkyne butane 2-butyne 1-butyne The “dots” are to help locate the linear, sp carbons of the alkyne triple bond.

Alkane …………Alkyne Alkyne Nomenclature 4-methylpentyne (S)-4-bromo-4,5-dimethyl-2-hexyne