Organomagnesium Reagents

Question 1

Magnesium-halogen exchange is ______ with electron poor substrates and _______ with electron-rich substrates.

Answer 1

Faster with electron poor substrates

slower with electron-rich substrates

Question 2

Aryl iodies react ______ than aryl bromides

Answer 2

faster

Question 3

What does DMG stand for? And what is the synonym?

Answer 3

Directed Metalation Group. Ortho-directing groups

Question 4

DMGs _________ the rate of magnesium-halogen exchange.

Answer 4

increase

Question 5

What does it mean for Grignard reagents to have ‘improved functional group tolerance?’ and what characteristic of Grignard reagent allows this?

Answer 5

Functional group tolerance in this sense means that the Grignard reagent does NOT reaction with certain functional groups. Low reactivity of Grignard reagent allows this.

Question 6

Does Grignard reagent show functional group tolerance at low or high temperature?

Answer 6

At low temperature, typically below 0 degree celcius.

Question 7

What is a condition for the improved functional group tolerance?

Answer 7

The rate of magnesium-halogen exchange needs to be sufficiently faster than the reaction rate of magnesium and the functional group.

Question 8

In the example in the lecture, Anilines are emplyed by using 2 equivalents of a Grignard reagent. State what the first equivalent and second equivalent Grignard reagent performs.

Answer 8

First equivalent deprotonates Aniline and the second equivalent performs the magnesium-halogen exchange.

Question 9

Magnesium-halogen exchange is relatively slow for _____iodide substrates.

Answer 9

Vinyl Iodide

Question 10

What is a Turbo Girgnard reagent? And what does it do?

Answer 10

i-PrMgCl.LiCl, increase the rate of magnesium halogen exchange with vinyl iodides.

Question 11

How does the LiCl increase the reactivity of the rest of Turbo Grignard reagent?

Answer 11

LiCl increases the reactivity of i-PrMgCl by breaking up aggregates.

Question 12

What is the dominant reactivity pathway observed with Grignard reagents?

Answer 12

Addition to carbonyl groups

Question 13

Is Grignard reagent more or less selective for carbonyl addition than organolithium reagents.

Answer 13

More selective

Question 14

How does the carbonyl group get activated by the first equivalent of Grignard reagent?

Answer 14

Mg ion in Grignard reagent activates carbonyl by acting as a Lewis acid and attracting electrons from carbonyl oxygen, leaving carbonyl carbon more electropositive.

Question 15

What does the second equivalent of Grignard reagent do in a reaction with a carbonyl group?

Answer 15

2nd equivalent Grignard acts as a nucleophile and delivers the R group.

Question 16

Does Grignard reagent react with carboxylates?

Answer 16

No, because the Grignard reagent is not nucleophilic enough to attack carboxylate.

Question 17

Does Organolithium react with carboxylate?

Answer 17

Yes, Organolithium can react with carboxylate and make ketone product.

Question 18

Grignard reagent is not sensitive/ sensitive to steric bulk around the carbonyl group.

Answer 18

Sensitive

Question 19

Grignard reagents are good/bad nucleophile and strong/ weak base

Answer 19

Good nucleophile

Strong base