CHAPT 5: Elimination Flashcards Preview

CHEM III organic chemistry > CHAPT 5: Elimination > Flashcards

Flashcards in CHAPT 5: Elimination Deck (11)
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1

what is Zaitzev's rule?

the preferred product is the most substituted Alkene

2

rule of elimination

in order for elimination to occur there must be a beta hydrogen on beta carbon
one beta carbon= one alkene product
2 diff beta carbon = 2 alkene product ( major is more sub alkene)

3

E2 and E1 mechanism

E2;
1. break C -beta hydrogen
2. break C-LG bond
3. form base - beta hydrogen bond
4. forms C=C

E1:
Step1 : formation of carbocation
step 2: break C - beta hydrogen bond
form base - beta hydrogen bond
form C=C bond

4

substrate preference

E2: no substrate preference as base attacks beta hydrogen not alpha carbon
E1: most stable carbocation= faster RDS= faster rxn

5

stereochemistry

E2: anti coplanar elimination is preferred
E1: no geometrical requirements as halide and beta hydrogen is lost in different step
- follows zaitsev's rule

6

what is syn elimination and anti elimination

syn elimination: both beta h and LG leave on same side
anti elimination : both beta h and LG leave on diff side

7

stereochemistry of cyclohexane in E1

a+a (anti) and e+e (syn) is coplanar
a+e not coplanar, no E2
coplanar arrangement allows pi bond formation
if orbitals are not coplanar, E2 mechanism cannot occur

8

anti-periplanar in newman projection

staggered conformation so there is less steric hindrance between the base and the LG as they are on the opposite side
for syn coplanar it will be eclipsed conformation and there will be repulsive interactions ( not stable)

9

elimination of alcohol substrates

protonation will always be first step
2* and 3* ( E1 mechanism )
1* ( E2 mechanism)

10

diff on E1 AND E2

E1 : weak base
rearrangement is possible
have intermediate

E2 : strong base
Rearrangement not possible
have TS

11

E1 VS SN1

nucleophilic attacks in SN1 are faster than the abstraction of the beta hydrogen by the weak base in E1.
there is also fewer bond breaking and bond forming step in SN1 mechanism.