1. Grignard’s reagents
understand methods of increasing the length of the carbon chain in a molecule by the use of magnesium to form Grignard reagents and the reactions of the latter with carbon dioxide and with carbonyl compounds in dry ether

2. A Grignard reagent has a formula RMgX where X is a halogen, and R is an alkyl or aryl (based on a benzene ring A typical Grignard reagent might be CH3CH2MgBr

3. How to prepare a Grignard
Grignard reagents are made by adding the halogenoalkane to small bits of magnesium in a flask containing ethoxyethane (commonly called diethyl ether or just "ether"). The flask is fitted with a reflux condenser, and the mixture is warmed over a water bath for minutes.
Everything must be perfectly dry because Grignard reagents react with water
ethoxyethane

4. How a Grignard reacts with water

5. Grignard and carbon dioxide
Grignard reagents react with carbon dioxide in two stages. In the first, you get an addition of the Grignard reagent to the carbon dioxide.
Dry carbon dioxide is bubbled through a solution of the Grignard reagent in ethoxyethane.
For example:

6. Grignard and carbon dioxide
The product is then hydrolysed (reacted with water) in the presence of a dilute acid. Typically, you would add dilute sulphuric acid or dilute hydrochloric acid to the solution formed by the reaction with the CO2.
A carboxylic acid is produced with one more carbon than the original Grignard reagent.

7. Reaction of Grignard with Aldehydes and Ketones.
Treatment of an aldehyde or ketone with a Grignard reagent followed by water forms an alcohol with a new carbon—carbon bond.
This reaction is an addition because the elements of R’’ and H are added across the  bond.

8. This reaction follows the general mechanism for nucleophilic addition

9. Note that these reactions must be carried out under anhydrous conditions to prevent traces of water from reacting with the Grignard’s reagent.

10. Retrosynthetic Analysis of Grignard Products
To determine what carbonyl and Grignard components are needed to prepare a given compound, follow these two steps:

11. Let us conduct a retrosynthetic analysis of 3-pentanol.

12. Let us conduct a retrosynthetic analysis of 3-pentanol.