Home >
Community >
Reaction involving opening of epoxides
Upvote
23
Downvote
+ Alcohols
+ Chemistry
Posted by
Ken Giuffre
Reaction involving opening of epoxides
As you are dealing with Grignard reagents, the carbocation argument is inadequate since the reaction is in basic media (carbocations are brønsted acids, so they would be easily deprotonated to produce an alkene). In fact, this mechanism is concerted (everything happens simultaneously, not in 2 distinct steps such as in the formation of a carbocation followed by a nucleophilic attack).
The Grignard reagent could attack either the methylene $\ce{(CH_2)}$ carbon or the methylidyne $\ce{(CH(CH_3))}$ carbon. The methylene carbon is attacked preferentially because its substituents are smaller than the methylidyne ones (2 hydrogens against one hydrogen and a methyl group). So steric hindrance is the key factor for predicting the product correctly in this question, not carbocation stability.
ps.: I drew a specific enantiomer just for visualization, but in this case, the absolute configuration doesn't matter.
As you are dealing with Grignard reagents, the carbocation argument is inadequate since the reaction is in basic media (carbocations are brønsted acids, so they would be easily deprotonated to produce an alkene). In fact, this mechanism is concerted (everything happens simultaneously, not in 2 distinct steps such as in the formation of a carbocation followed by a nucleophilic attack).
The Grignard reagent could attack either the methylene $\ce{(CH_2)}$ carbon or the methylidyne $\ce{(CH(CH_3))}$ carbon. The methylene carbon is attacked preferentially because its substituents are smaller than the methylidyne ones (2 hydrogens against one hydrogen and a methyl group). So steric hindrance is the key factor for predicting the product correctly in this question, not carbocation stability.
ps.: I drew a specific enantiomer just for visualization, but in this case, the absolute configuration doesn't matter.
Grignard reagents are generally bulky in nature therefore they choose to attack the less sterically hindered carbon which in this case is the methylene carbon .
Furthermore you should remember that presence of acidic media will destroy the Grignard reagent . The carbocation stability is not considered only because it is a bronsted lowry acid.
Grignard reagents are generally bulky in nature therefore they choose to attack the less sterically hindered carbon which in this case is the methylene carbon .Furthermore you should remember that presence of acidic media will destroy the Grignard reagent . The carbocation stability is not considered only because it is a bronsted lowry acid.
When you are using Grignard reagent for opening of epoxides, the Grignard reagent will attack less sterically hindered carbon(i.e. SN2 attack will take place). This is because when we use Grignard reagent, the reaction takes place in basic medium. Therefore in step 3 it will attack the 1st carbon instead of the 2nd one.
When you are using Grignard reagent for opening of epoxides, the Grignard reagent will attack less sterically hindered carbon(i.e. SN2 attack will take place). This is because when we use Grignard reagent, the reaction takes place in basic medium. Therefore in step 3 it will attack the 1st carbon instead of the 2nd one.
As you are dealing with Grignard reagents, the carbocation argument is inadequate since the reaction is in basic media (carbocations are brønsted acids, so they would be easily deprotonated to produce an alkene). In fact, this mechanism is concerted (everything happens simultaneously, not in 2 distinct steps such as in the formation of a carbocation followed by a nucleophilic attack).
The Grignard reagent could attack either the methylene $\ce{(CH_2)}$ carbon or the methylidyne $\ce{(CH(CH_3))}$ carbon. The methylene carbon is attacked preferentially because its substituents are smaller than the methylidyne ones (2 hydrogens against one hydrogen and a methyl group). So steric hindrance is the key factor for predicting the product correctly in this question, not carbocation stability.
ps.: I drew a specific enantiomer just for visualization, but in this case, the absolute configuration doesn't matter.
As you are dealing with Grignard reagents, the carbocation argument is inadequate since the reaction is in basic media (carbocations are brønsted acids, so they would be easily deprotonated to produce an alkene). In fact, this mechanism is concerted (everything happens simultaneously, not in 2 distinct steps such as in the formation of a carbocation followed by a nucleophilic attack).
The Grignard reagent could attack either the methylene $\ce{(CH_2)}$ carbon or the methylidyne $\ce{(CH(CH_3))}$ carbon. The methylene carbon is attacked preferentially because its substituents are smaller than the methylidyne ones (2 hydrogens against one hydrogen and a methyl group). So steric hindrance is the key factor for predicting the product correctly in this question, not carbocation stability.
ps.: I drew a specific enantiomer just for visualization, but in this case, the absolute configuration doesn't matter.
More
VOTE
Grignard reagents are generally bulky in nature therefore they choose to attack the less sterically hindered carbon which in this case is the methylene carbon . Furthermore you should remember that presence of acidic media will destroy the Grignard reagent . The carbocation stability is not considered only because it is a bronsted lowry acid.
Grignard reagents are generally bulky in nature therefore they choose to attack the less sterically hindered carbon which in this case is the methylene carbon .Furthermore you should remember that presence of acidic media will destroy the Grignard reagent . The carbocation stability is not considered only because it is a bronsted lowry acid.
More
VOTE
When you are using Grignard reagent for opening of epoxides, the Grignard reagent will attack less sterically hindered carbon(i.e. SN2 attack will take place). This is because when we use Grignard reagent, the reaction takes place in basic medium. Therefore in step 3 it will attack the 1st carbon instead of the 2nd one.
When you are using Grignard reagent for opening of epoxides, the Grignard reagent will attack less sterically hindered carbon(i.e. SN2 attack will take place). This is because when we use Grignard reagent, the reaction takes place in basic medium. Therefore in step 3 it will attack the 1st carbon instead of the 2nd one.
More
VOTE