-
Electrophilic addition
- alkenes and alkynes(similar mechanism)
- electrophile attacks pi orbital e-'s
- forms carbocation
- Follows Markovnikovs Rule
- Nu attacks carbocation
- can stop at alkene unless excess added
- anti or syn addition
-
Regiospecific reaction
- only one of two possible products produces
- due to TS carbocation
- seen in addition of HX
-
Regioselective Reaction
a little of the nonpredominant orientation is formed
-
Markovnikovs rule
- H adds to least substituted carbon (C with most H's)
- X binds to more alkyl substituted carbon
-
Addition of Halogens X2
- usually Cl2 or Br2 with nuetral solvent
- CHCl3 or CCl4F2 too reactive
- I2 not reactive enough
- Br2 used to test for unsaturation
- forms the "hug" - bromium ion
- c=c is sp2, therefore flat
- in cyclic...adds trans
-
if addition is in alkene existing as E or Z geometrical isomer than....
3 (if one meso) or 4 dihaloalkanes steroisomers are formed
-
halogenation of alkynes (ie with Br2) always
a) produces trans alkene
b)produces cis alkene
c)doesnt react
d) produces both cis and trans
produces trans alkene
-
Halohydrin formation
- alkene(yne)+ X2
- occurs in nucleophilic solvent (water or methanol)
- solvents compete for carbocation
- win only becuase of amount available
- produces alcohol
- forms "hug"
- then backside Nu attack
- can produce hydronium in water
- also forms epoxides!!
-
addition of water to alkenes
- similar to HX but requires strong acid catalyst
- floows markovnikovs rules
- cis , trans and enantiomers formed
- invilves racemization due to C+
-
Oxymercuration (reduction)
- hydrates a multiple bond
- uses Mercury (II) acetate,water, NaOH and NaBH4creates alcohol
-
tautomerism
- seen in oxymercuration (keto-enol tautomerism)
- In organic chemistry, keto-enol tautomerism refers to a chemical equilibrium between a keto form (a ketone or an aldehyde) and an enol (An alcohol). The enol and keto forms are said to be tautomers of each other. The interconversion of the two forms involves the movement of a proton and the shifting of bonding electrons; hence, the isomerism qualifies as tautomerism.
-
Hydroboration
- BH3, THF added with alkene first
- then H2O2 and NaOH
- anti-markovnikovs rule
- source of hard to get alcohols
- BH3 forms diborane
- also exists as complex with THF
- forms trialkylborane
-
hydroboration with alkynes forms intermediate ____________ and final product is a __________
|
|
