Advices For Studying Organic Chemistry

4. All these methods will be likely to give the desired compound in greater than 80%
   yields.

12.8B RESTRICTIONS ON THE USE OF GRIGNARD REAGENTS

1. The Grignard reagent is a very powerful base ⇒ it is not possible to prepare a
   Grignard reagent from an organic group that contains an acidic hydrogen.


2. Grignard reagents are powerful nucleophiles ⇒ it is not possible to prepare a
   Grignard reagent from any organic halide that contains a carbonyl, epoxy, nitro, or
   cyano group.

–OH, –NH 2 , –NHR, –CO 2 H, –SO 3 H, –SH, –C≡C–

CH

O

, CR

O

, COR

O

, CNH 2

O
, –NO 2 , –C≡N, C C
O
Grignard reagents containing these groups cannot be prepared.
This means that when we prepare Grignard reagents, we are effectively limited to alkyl
halides or tro analogous organic halides containing C=C bonds, internal triple bonds,
ether linkages, and –NR 2 groups.

3. Grignard reactions are so sensitive to acidic compounds that special care must be
   taken to exclude moisture from the apparatus and anhydrous ether must be used as
   the solvent.


4. Acetylenic Grignard reagents:

C 6 H 5 CCCH +C 2 H 5 MgBr 6 H 5 C CMgBr +C 2 H 6 ¡ô

C 6 H 5 CCCMgBr + C 2 H 5 CH + 6 H 5 C C CHC 2 H 5

O

2. H 3 O OH
   ( 52 %)