Alkenes Properties Nomenclature Stability Addition Reactions Ethylene Electron
Alkenes Properties Nomenclature Stability Addition Reactions
Ethylene
Electron Rich p-Bond
Elements or Degrees of Unsaturation: p-Bond or Ring
Determine the # elements of Unsaturation
Alkene Nomenclature
Cyclic alkenes
Alkyl Groups with p-Bonds
Alkylidene Groups Double Bonds Fused to Rings
Polyenes
Name these Alkenes
Cis and Trans no rotation about p-bond
cis-trans Isomers
E/Z System
Establish Priority of 2 Substituents on Each sp Carbon
What’s My Name?
(Z)-4 -ethyl-5 -isopropyl-4 -nonene
Priorities with Multiple Bonds
E or Z?
E or Z?
Name These
Hydrogenation Data Helps to Determine Stability DHhydrogenation 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 HCl Markovnikov Addition
Regiochemistry Determined by Stability of Intermediate
Hyperconjugation
Carbocation Stability more highly substituted, lower energy
3 o 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:
Rearrangements
Propose a Mechanism
- Slides: 54