Chapter 7: Alkenes and Alkynes I
CH 7-1 Introduction
•Structure of alkenes & alkynes
•Nomenclature
•Relative stabilities of alkenes
•Synthesis of alkenes via E1/E2 eliminations:
 E2 with small or bulky base
 Stereochemistry in E2 eliminations
 Cycloalkene eliminations
 Acid catalyzed alcohol dehydration
•Rearrangements in SN1/E1 reactions
•Alkene Hydrogenation (stereospecific syn addition of H2)
•Terminal alkynes as nucleophiles
Structure of Alkenes
•“Un-saturated hydrocarbons” – contain C=C which is the
key to understanding alkene chemical reactivity, HD = 2
• sp2 hybridization; trigonal planar; sigma and pi bonds
•Each sp2 carbon has 3 sigma bonds & 1 pi bond. No C=C
bond rotation due to the pi bond.
s
cis-2-butene
p-orbitals “overlap”
• Alkenes have Constitutional and Geometric isomers (cistrans). How many isomers exist for the formula: C4H8
Structure of Alkynes
•“Un-saturated hydrocarbons” – contain C-C triple bond.
• Linear geometry; sp hybridization; sigma and pi bonds
H3C
C
C
CH3
• Alkynes have Constitutional isomers (no geometric).
How many isomers exist for the formula:
C 4H 6
(Hint: nine isomers: 3 alkyne, 2 alkene, 4 ring)