Main Contents Stability of alkenes Preparing alkenes:a preview EA Reactions of alkenes Carbocation structure and stability Reduction oxidation of alkenes Biological additions of Radicals to alkenes ■Conjugated Dienes ■Reactions of alkynes
Main Contents Stability of alkenes Preparing alkenes: a preview EA Reactions of alkenes Carbocation structure and stability Reduction & oxidation of alkenes Biological additions of Radicals to alkenes Conjugated Dienes Reactions of alkynes
Sec 1 Alkenes structure and stability Molecule is planar around the double bond. 口 The carbon atoms of the C=C bond are sp hybridized and Double bond is made up of one o bond and one bond. Bond rotation round a C=C bond is not possible Isomers are possible depending on the substituents present. CH3 CH3 cis no overlap with the ends perpendicular trans Copyright 2010 Pearson Prentice Hall,Inc
Sec 1 Alkenes structure and stability Molecule is planar around the double bond. The carbon atoms of the C=C bond are sp hybridized and Double bond is made up of one σ bond and one π bond. Bond rotation round a C=C bond is not possible Isomers are possible depending on the substituents present
Bond Lengths and Angles -Pi overlap brings carbon atoms closer. -Bond angle with pi orbital increases. ·Angle C=C-His121.7°；Angle H-C-His116.6 -Cis and trans isomers cannot be interconverted -No rotation around the carbon-carbon 1.33 116.6° H ethylene ethane
Bond Lengths and Angles Pi overlap brings carbon atoms closer. Bond angle with pi orbital increases. Angle C=C-H is 121.7° ;Angle H-C-H is 116. 6° Cis and trans isomers cannot be interconverted. No rotation around the carbon—carbon
Cyclic Alkene Compounds cyclohexene cyclooctene trans-cyclodecene cis-cyclodecene Copyright 2010 Pearson Prentice Hall,Inc. -Trans cycloalkenes are not stable unless the ring has at least eight carbons. -Cycloalkenes are assumed to be cis unless otherwise specifically named frans
Cyclic Alkene Compounds Trans cycloalkenes are not stable unless the ring has at least eight carbons. Cycloalkenes are assumed to be cis unless otherwise specifically named trans
Stability of Alkenes Stability of cis and trans isomers Interconversion does not occur spontaneously but can be induced by strong acid H CH3 H3C、 CH3 Acid C=C catalyst H3C Trans (76%) Cis(24%) Steric strain cis-But-2-ene trans-But-2-ene
Stability of cis and trans isomers • Interconversion does not occur spontaneously but can be induced by strong acid Stability of Alkenes