Transcript Alkenes - University of Illinois at Urbana–Champaign

Alkenes
CnH2n
sp2 hybridized carbons
p
p
sp2
s
H
H
C
C
H
H
Alkenes
Cl
Cl
Cl
H
cisCl
Cl
no rotation at C=C
trans-
HCl
geometric isomers
Nomenclature
1.
2.
3.
4.
5.
6.
Longest chain with C=C is parent.
C numbered from end nearest to C=C.
Designate cis- or trans- if necessary.
Name substituents.
Replace ane with ene ending.
If more than one C=C, give smallest
numbers and call diene or triene.
Nomenclature
1
2
3
4
6
5
8
7
trans- 2- octene
cis- 2- octene
trans- 5-methyl-3-propyl-1,3- hex adiene
1
3
2
5
4
3-propyl
6
5-methyl
Alkene - reactions
 electrons Lewis Base
Lewis Base e- pair donor
nucleophile
Lewis Acid e- pair acceptor
electrophile
Addition Reactions
+
Hrxn = bonds broken - bonds formed
Hrxn = (-bond + -bond) - (2 -bonds) < 0
exothermic
Addition of HX
H3C
H
C C
H
H
+
H+ + Cl-
reaction mechanism
H3C H
H C C H
Cl H
H3C H
H C C H
H Cl
Lewis base
 electrons
nucleophile
Lewis acid
H+
electrophile
Addition of HX
step 1
H3C
H
H
C
C
H
+ H-Cl
H+ + Cl-
H+
2o carbocation
1o carbocation
Addition of HX
2o carbocation
1o carbocation
most stable intermediate
Stability of carbocations 3o >2o >1o
carbocations are e- deficient
electrophiles react with nucleophile
Lewis acids
Lewis base
Addition of HX
step 2
major product
minor product
Markovnikov’s Rule
major product
minor product
2-chloropropane
1-chloropropane
C with the most H gets the H
Alkane Summary
1. Alkanes - sp3 hybridized
2. Relatively unreactive
Substitution with halogens (hn)
Combustion
3. Non-polar
IMF = London Dispersion Forces
size
structure
4. Free rotation around C-C bonds
conformations
5. Non-cyclic alkanes - structural isomers
6. Cyclic alkanes - geometric isomers
cis-, trans7. Alkanes - optical isomers
stereocenters
C*