Week 7 Flashcards
when do you see a 1-2 hydride shift
2’ to 3’ carbocation because it’s more stable
when do you see a 1-2 methyl shift
only a bit, rationalize unexpected product
degrees of unsaturation
rings and double bonds
(2n+2 - H - halogens + N) / 2
Markovnikov’s rule and extension with carbocations
H goes to C with more H’s
more substituted / higher degree C is more stable and therefore will produce predominate structure
REACTION GOES THROUGH MORE STABLE CARBOCATION
Hammond’s postulate
transition state resembles nearest stable species
planar carbocation
if you think about it, all carbocations are planar so incoming nucleophile can attack re or si face with equal probability
resonance structures
don’t forget!
determining factors in addition selectivity
- regioselectivity - Mark’s rule, most stable carbocation intermediate
- stereochemistry - not selective, added to both faces of carbocation
syn vs anti addition
syn = same face
anti = opposite face
all relative to R groups
polarizability
bond can be polar or non polar but atoms can be large and so the bond is weaker and therefore easily polarizable
why do we use NBS for bromohydrin formation
Br2 is nasty so NBS which has weak N-Br BOND that can be electrophile
anti addition with X2 and
What is always the nucleophile? What does changing the electrophile do?
Nucleophile is always alkene
Electrophile changing leads to selectivity of regiochemistry and stereochemistry
anti addition with X2 and different solvents (2)
- non H2O or ROH (alcohol) solvents
- solvent mixtures off H2O and THF or PMSO to give 2 alcohol enantiomers
Exo/Endothermic vs Exer/Endergonic
Exo/Endothermic represents the relative change in heat/enthalpy in a system, whereas Exer/Endergonic refers to the relative change in the free energy of a system
