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Alkenes
PropertiesNomenclature
StabilityAddition Reactions
Ethylene
Electron Rich -Bond
Elements or Degrees of Unsaturation: -Bond or Ring
Determine the # elements of Unsaturation
C8H10Br2OC8H18 is saturatedcompound is deficient by 6 "H's"3 degrees of unsaturation
O
BrBrCH2OH
CH3
Br
Br
e.g.
OH Br
Br
Alkene Nomenclature
Cyclic alkenes
Alkyl Groups with -Bonds
CH=CH2
Br
cis 1-bromo-3-vinylcyclohexane
a vinyl group CH2CH=CH2
4-allylcyclopentene
an allyl group(or ethenyl)(or 2-propenyl)
a phenyl group
3-phenyl-1-nonene
Alkylidene GroupsDouble Bonds Fused to Rings
CH2
methylenecyclohexane
CHCH3
ethylidenecyclopentane
Polyenes
Name these Alkenes
Cis and Transno rotation about -bond
cis-trans Isomers
E/Z System
Establish Priority of Substituents on Each sp2
Carbon
What’s My Name?
(Z)-4-ethyl-5-isopropyl-4-nonene
Hi
Hi
Lo
Lo
Priorities with Multiple Bonds
E or Z?
E or Z?
Name These
3,3-dimethyl-1,4-cyclohexadiene 2-butyl-1,5-hexadiene
(E) 1-ethylidene-2-methylcyclopentane3-allylcyclohexene
Hydrogenation Data Helps to Determine Stability
Hhydrogenation of Alkenes
Enthalpy Change Shows Relative Energy of Alkene
Both cis and trans 2-Butene are Hydrogenated to Butane
“E” is More Stable than “Z” by 2.3 KJ/mol
Relative Stabilities of Alkenes
The Addition Reaction
HBr Addition
Markovnikov’s Rule
The addition of H-X across a double bond results in the more
highly substituted alkyl halide as the major product.
Depicting a Reaction
Addition of HBr or HClMarkovnikov Addition
Markovnikov
Br
C CH
H
HCH3
CH3
HBr
CH3
CH3
CH
HC
CH3
CH3C
H
H
Br
C
H
not formed
Regiochemistry Determined by Stability of Intermediate
H-BrBr
H
HBr Br H
3o carbocation
Hyperconjugation
Carbocation Stabilitymore highly substituted, lower energy
3o Carbocation forms Preferentially
What Alkenes are Needed to form Theses Alkyl Halides?
Definitions• Regioisomers – two constitutional isomers
that could result from an addition reaction. • Regiospecific – only one regiosisomer
forms at the expense of the other.• Regioselective – both regioisomers are
formed, but one is formed in preference.
Determine the major product:
a) HCl
b)HBr
c) 2 mol HCl
a) HCl
b)HBr
c) 2 mol HCl
Cl
H
BrH
Cl ClHH
cis and trans
RearrangementsCH3
CH3
HCl CH3
CH3
Cl
HH Cl
CH3
CH3
H
methide shiftCH3
CH3
Cl
32o o
Propose a Mechanism