- ALKENE STABILITY!
- WHICH IS MORE STABLE?
- THE TRANS STEREOISOMER IS MORE STABLE THAN THE CIS STEREOISOMER SINCE THE TRANS DOES NOT HAVE THE STERIC INTERFERENCE (STRAIN) THAT THE CIS DOES!
- cis-2-BUTENE --?--> trans-2-BUTENE
- ---and---
- trans-2-BUTENE --?--> cis-2-BUTENE
- THESE REACTIONS DO NOT OCCUR READILY!
- BUT, WITH AN ACID CATALYST
- CAN'T ALWAYS EQUILIBRATE
- NEED ANOTHER WAY TO DETERMINE RELATIVE ENERGIES
- CONVERT THE TWO ALKENES IN QUESTION TO A COMMON PRODUCT AND COMPARE ENERGIES
- a. HYDROGENATION
- TRANS-2-BUTENE + H2 ---> BUTANE + 27.6 kcal/mol
- CIS-2-BUTENE + H2 ---> BUTANE + 28.6 kcal/mol
- 1-BUTENE + H2 ---> BUTANE + 30.1 kcal/mol
- BOTH CIS- AND TRANS-2-BUTENE ARE MORE STABLE THAN 1-BUTENE
- CAN WE COMPARE 1-BUTENE AND ISOBUTYLENE?
- b. COMBUSTION!
- 1-BUTENE + 6 O2 ---> 4 CO2 + 4 H2O + ENERGY
- ISOBUTYLENE + 6 O2 ---> 4 CO2 + 4 H2O + ENERGY
- ENERGY DIFFERENCE IS ABOUT 1.7 kcal/mol WITH ISOBUTYLENE BEING LOWER IN ENERGY
- GENERALIZATION
- WHICH IS MORE STABLE?
Answer
- ALKYL GROUPS STABILIZE AN ALKENE MORE THAN A HYDROGEN DOES.
- THIS STABILIZATION MORE THAN OFFSETS THE STERIC EFFECT OF TWO ALKYL GROUPS CIS TO EACH OTHER.
- WHICH IS MORE STABLE?
Answer
- WHICH IS MORE STABLE, (E)-4-METHYL-2-HEPTENE or (E)-4-METHYL-3-HEPTENE?
- ELECTROPHILIC ADDITION TO ALKENE
- REACTION IS OFTEN RUN IN ETHER SOLVENT
- WRITE IN DIFFERENT WAYS DEPENDING ON EMPHASIS.
- IS THE REACTION GENERAL, WILL IT WORK WITH OTHER ALKENES?
- IN ALL CASES THE HALOGEN WENT TO THE MORE HIGHLY SUBSTITUDED CARBON.
- REACTION IS REGIOSELECTIVE
- WHEN A REACTION WHICH CAN POTENTIALLY YIELD TWO OR MORE CONSTITUTIONAL ISOMERS ACTUALLY PRODUCES A PREPONDERANCE OF ONE, THE REACTION IS SAID TO BE REGIOSELECTIVE.
- NOTE
- MARKOVNIKOV'S RULE!
- IN THE IONIC ADDITION OF ACID HX TO AN ALKENE, THE HYDROGEN OF THE ACID ATTACHES TO THE CARBON OF THE ALKENE WHICH HAS THE LARGER NUMBER OF HYDROGENS.
- PREDICT THE PRODUCT:
Answer 
Answer - WHICH ALKENE IS NEEDED TO SYNTHESIZE:
Answer
- WHY DO WE HAVE MARKOVNIKOV'S RULE?
- IT APPEARS THAT TERTIARY CARBOCATIONS ARE MORE STABLE THAN SECONDARY CARBOCATIONS WHICH ARE MORE STABLE THAN PRIMARY CARBOCATIONS.
- 3o > 2o > 1o > METHYL CARBOCATION
- OTHER EVIDENCE:
- STABLE SALTS OF (CH3)3C+1 HAVE BEEN MADE BUT NOT CH3CH2CH2CH2+1
- TAKES LESS ENERGY TO MAKE (CH3)3C+1 FROM (CH3)3CCl THAN CH3+1 FROM CH3Cl
- STRUCTURE OF METHYL CARBOCATION
- WHY ARE TERTIARY CARBOCATIONS MORE STABLE THAN SECONDARY, ETC?
- INDUCTIVE EFFECT
- WHICH IS MORE STABLE?