Chapter 6 Flashcards
addition to alkenes
break the double bond and add two new single bonds
reaction mechanism
how we get from starting material to product
4 basic mechanism elements
- Nucleophilic Attack (make a bond)
- Proton abstraction (remove hydrogen)
- Protonation (add hydrogen)
- Departure of a leaving group (break a bond)
reactive intermediate
high energy species formed between two successive reaction steps, that lies in an energy minimum between the two transitions states
rate-determining step
the step in a multistep reaction sequence that has the highest energy barrier
bond dissociation enthalpies
amount of energy required to break a bond into two radicals (in the gas phase)
electrophilic addition
electrophilic species adds across a double bond
inductive effects
spreading (=delocalizing) charge by polarizing e- toward the e- deficient carbocation
hyperconjugation
interaction of electrons in a pi bonding orbital w/ vacant 2p orbital of adjacent positively charged carbon
carbocations
often intermediates
regioselective reaction
addition or substitution reaction where one out of multiple possible products is formed
Markovnikov’s Rule
when hydrogen adds to the carbon of the double bond that has the greater number of hydrogen’s in an electrophilic addition reaction of alkenes
hydration
the addition of water
-regioselective: Markovnikov addition
Markovnikov regioselectivity
-H goes onto the carbon with more hydrogens
rearrangement
change in connectivity of the atoms
1,2 shift
a type of rearrangement in which an atom of atoms with its bonding electrons moves from one atom to an adjacent electron-deficient atom
stereoselective reaction
a reaction in which one stereoisomer is formed in preference to all
antistereoselectivity
the addition of atoms or groups of atoms to opposite faces of a carbon-carbon double bond
halohydrin
compound containing a halogen and a hydroxyl group on adjacent carbons
- vicinal atoms are bonded to adjacent carbons, whereas geminal atoms are bonded to the same carbon
regioselective: halogen goes on less substituted carbon, hydroxyl goes on more substituted carbon - stereoselective: halogen and hydroxyl add from opposite face of the double bond
oxymercuration
a method for converting an alkene to an alcohol
- uses mercury (II) acetate (Hg(OAc)2) followed by reduction with sodium borohydride (NaBH4). Occurs w/o arrangement
- regioselective: Markovnikov addition
- stereoselective: Initially -HgOAc and -OH add from the opposite face of the double bond (anti stereoselective), but that stereoselectivity is removed when the -H is scrambled upon reduction of -HgOAc.
reduction
the gain of electrons. Gain of hydrogen/loss of oxygen
hyboration-oxidation
a method for converting an alkene into an alcohol. occurs without rearrangement
- regioselective: non-Markovnikv addition (-H goes onto carbon with fewer hydrogens)
- stereoselective: hydrogen and boron add from the same face of the double bond (syn stereoselective)
oxidation
the loss of e-. Alternatively, the loss of hydrogen and or Bain of oxygen
-stereoselective: both hydroxyl groups add from the same face of the double bond (syn stereoselective)
ozonolysis
cleavage of a double double bond with ozone, producing two carbonyl (C=O) groups in its place
hydrogenation
reduction with molecular hydrogen (H2). Often used to create saturated hydrocarbons from unsaturated ones
-stereoselctive: both hydrogens add from the same face of the double bond (syn stereoselective)
stereospecific reaction
a reaction in which the stereochemistry of the product depends on the stereochemistry of the starting material
A. achiral starting material in an achiral environment
B. chiral starting material in an achiral environment
C. achiral starting material in a chiral environment
enantioselective
a reaction that produces one enantiomer in preference to the other
