Advices For Studying Organic Chemistry

C

C

H 3 C H

H 3 C H

1. RC(O)OOH
   H 2 O

HO

OH HO

OH

2. HA,

C

C

H

CH 3

H CH

3

C

C

H

CH 3

H CH^3

cis-2-Butene (S,S)

Enantiomeric 2,3-butanediols

(anti hydroxylation)

(R,R)

C

C

H CH 3

H 3 C H

1. RC(O)OOH
   H 2 O

HO

HO

2. HA,

C

C

CH (^3) H
H
CH 3
trans-2-Butene meso-2,3-Butanediols
(anti hydroxylation)
Figure 11.4 The overall result of epoxidation followed by acid-catalyzed hydrolysis
is a stereospecific anti hydroxylation of the double bond. cis-2-Butene
yields the enantiomeric 2,3-butanediols; trans-2-butene yields the meso
compound.

11.20 CROWN ETHERS: NUCLEOPHILIC SUBSTITUTION

REACTIONS IN RELATIVELY NONPOLAR APROTIC

SOLVENTS BY PHASE-TRANSFER CATALYSIS

1. SN2 reactions take place much more rapidly in polar aprotic solvents.
   
   
   1. In polar aprotic solvents the nucleophile is only very slightly solvated and is,
      consequently, highly reactive.
   
   
   2. This increased reactivity of nucleophile is a distinct advantage ⇒ Reactions that
      might have taken many hours or days are often over in a matter of minutes.
   
   
   3. There are certain disadvantages that accompany the use of solvents such as
      DMSO and DMF.
      i) These solvents have very high boiling points, and as a result they are often
      difficult to remove after the reaction is over.
      ii) Purification of these solvents is time consuming, and they are expensive.
      iii) At high temperatures certain of these polar aprotic solvents decompose.