Some of the most useful compounds for organic synthesis are...

Some of the most useful compounds for organic synthesis are Grignard reagents (general formula $\mathrm{R}-\mathrm{MgX},$ where $\mathrm{X}$ is a halogen), which are made by combining a haloalkane, $\mathrm{R}-\mathrm{X},$ with Mg. They are used to change the carbon skeleton of a starting carbonyl compound in a reaction similar to that with $\mathrm{R}-\mathrm{Li}:$ (a) What is the product, after a final step with water, of the reaction between ethanal and the Grignard reagent of bromobenzene? (b) What is the product, after a final step with water, of the reaction between 2 -butanone and the Grignard reagent of 2 -bromopropane? (c) There are often two (or more) combinations of Grignard reagent and carbonyl compound that will give the same product. Choose another pair of reactants to give the product in part (a). (d) What carbonyl compound must react with a Grignard reagent to yield a product with the $-\mathrm{OH}$ group at the $e n d$ of the carbon chain? (e) What Grignard reagent and carbonyl compound would you use to prepare 2 -methyl-2-butanol?

Key Concepts

Grignard Reagents

Grignard reagents are organometallic compounds, typically represented as R–MgX, in which a carbon atom bonded to magnesium carries a significant carbanion character. This makes them strongly nucleophilic and able to attack electrophilic centers, particularly the carbonyl carbon in carbonyl compounds, leading to the creation of new carbon–carbon bonds.

Carbonyl Compound Reactivity

Carbonyl compounds contain a carbon-oxygen double bond, which is polarized due to the electronegativity difference between carbon and oxygen. This polarization renders the carbon atom electrophilic and susceptible to nucleophilic attack, particularly by strongly nucleophilic species such as the carbanionic component of a Grignard reagent.

Nucleophilic Addition Mechanism

The reaction of a Grignard reagent with a carbonyl compound proceeds via a nucleophilic addition mechanism where the nucleophilic carbon of the Grignard reagent attacks the electrophilic carbon of the carbonyl group. This forms a tetrahedral alkoxide intermediate. The process is fundamental to forming new carbon–carbon bonds in organic synthesis.

Hydrolysis (Workup) Step

After the initial nucleophilic addition, a subsequent step involving water or a dilute acid, referred to as the hydrolysis or workup step, protonates the alkoxide intermediate. This converts the alkoxide into the corresponding alcohol, finalizing the synthesis and stabilizing the product.

Carbon–Carbon Bond Formation

Grignard reactions exemplify one of the most powerful methods in organic synthesis for forming carbon–carbon bonds. By choosing appropriate combinations of Grignard reagents and carbonyl compounds, chemists can systematically build up or modify the carbon skeleton of a molecule, enabling the synthesis of a wide variety of complex organic structures.

Transcript

00:01 Okay, so we're going to take the products and the following reactions, and the first one is reacting burma benzene with ethanol, and this is done over water.

00:10 So burma benzine, benzene is an aromatic ring with alternating double and single bonds, and this is reacting with saddian brumann in here.

00:33 Ethanol is, so ethene is two carbons, and the ale ending implies of an outahead.

00:45 So it looks like this.

00:47 And we react these structures it's going to so the greenery region of brambenzine is actually benzol magnesium bermad or some other metal reacting with an acolytid and because the magnesium is less electrophil than the carbon the carbon is going to be the nucleophile and this is going to attack the carbonal carbon because the oxygen draws lexon density away from the carbon of the aldehyde and makes it more electrophilk, it's susceptible to attack.

01:23 So if we, and when reacting with water, it's going to turn the oxytion, which is an oxygen with three limb pairs into an alcohol.

01:34 And we're going to add the benzene ring to this substitute.

01:40 So if we redraw this, we have this, and we're going to have two carbons here.

01:52 So we can draw like that.

01:53 And carbon one is an alcohol.

01:58 Let me get that structure.

02:02 The second one is reaction between 2 butanone and the greenerine region of 2 bromide propane.

02:11 So propane is 3 carbons.

02:13 And the bromine is on carbon 2.

02:17 And the greenerrean region of that is going to be a structure.

02:33 And so you're acting with 2 butanone.

02:38 So butane's 4 carbons, the own giving us a ketone.

02:41 And again, this is going to make this carbon nucleophilic.

02:44 So it's going to attack the carbonal carbon, which is very electrophilic.

02:50 And water will give us an alcohol.

02:51 You could also use an acid too like h3 plus or some other strong acid so we're going to get alcohol here in addition to the group we just added which is um this uh three carbon side chain actually if we read draw this so we have one two and then carbon two is attacking carbon three four and five so have a five carbon chain and carbon two has a methyl group right here carbon 3 became an alcohol, which is this one right here.

03:45 And 4 and 5 as a carbon 3 also has this methyl group right here as well.

03:54 So in reality, it's going to be this structure.

03:57 And to name this, it would be 2 -3 dimethyl 3 -petanol for c.

04:10 We have, so a different combination to give the product in a.

04:17 And we could also do...

04:21 Okay, so we want to create this structure.

04:24 And we obviously can't use the same reactants as before but we're going to start with benzene and we know we know we know we know we need to use either a ketone or an aldehyde and some granaryl region to attack it and if we use an aldohide and react this with methyl an an acet it's going to make this carbon nucleophilic and it's going to attack the carbon of carbon and you have some products so this is a carbon.

05:09 This will be the ch3 group that we added, and this is the hydrogen that's right here...

Please give Ace some feedback