1 Chapter 12 Alkenes and Alkynes Geometric Isomers of Alkenes

2 Saturated and Unsaturated Compounds Saturated compounds (alkanes) have the maximum number of hydrogen atoms attached to each carbon atom Unsaturated compounds have fewer hydrogen atoms attached to the carbon chain than alkanes Unsaturated compounds contain double or triple bonds

3 Comparing Alkanes, Alkenes, and Alkynes AlkaneAlkeneAlkyne General Formula C n H 2n+2 C n H 2n C n H 2n-2 Molecular Formula C2H6C2H6 C2H4C2H4 C2H2C2H2 NameEthaneEthene (ethylene) Ethyne (acetylene) Bond angle Geometry 109.5° tetrahedral 120 ° planar 180° linear

4 Alkenes  Carbon-carbon double bonds  Names end in -ene H 2 C=CH 2 ethene (ethylene) H 2 C=CH-CH 3 propene (propylene) cyclohexene

5 Alkynes  Carbon-carbon triple bonds  Names end in -yne HC  CHethyne(acetylene) HC  C-CH 3 propyne

6 Naming Alkenes and Alkynes When the carbon chain has 4 or more C atoms, number the chain to give the lowest number to the double or triple bond CH 2 =CHCH 2 CH 3 1-butene CH 3 CH=CHCH 3 2-butene CH 3 C  CCH 3 2-butyne

7 Naming Alkenes and Alkynes Name and number all groups bonded to the parent alkene or alkyne, and place the name and number in front of the name of the parent compound CH 3 C=CHCH 3 2-chloro-2-butene Cl

8 You Try These! Write the IUPAC name for each of the following unsaturated compounds: A.CH 3 CH 2 C  CCH 3 CH 3 B. CH 3 C=CHCH 3 C.

9 Answers to You Try These! Write the IUPAC name for each of the following unsaturated compounds: A. CH 3 CH 2 C  CCH 3 2-pentyne CH 3 B. CH 3 C=CHCH 3 C. 2-methyl-2-butene 3-methylcyclopentene

10 Naming Alkenes and Alkynes If more than one double or triple bond is present, indicate the position of each and use one of the suffixes – diene, -triene, and so on. CH 2 =C-CH=CH 2 CH 3 2-methyl-1,3- butadiene

11 Cis and Trans Isomers  Double bond is fixed  Cis/trans Isomers are possible CH 3 CH 3 CH 3 CH = CH CH = CH cis trans CH 3