The glassware used for a Grignard reaction is washed with water and acetone and dried thoroughly before the reaction is performed.

Select the most likely reason why:

A. Acetone is needed to react with the silanol groups on the surface of the glassware.
B. The acetone adheres to the sides of the glassware as it dries, catalyzing the formation of the Grignard reagents.
C. If the glassware is not completely dry, residual water or acetone will react with the Grignard reagent.
D. Grignard reactions are highly endothermic, and residual water will freeze during the reaction.

The reason for thoroughly washing and drying glassware before performing a Grignard reaction is primarily to ensure that the reaction proceeds effectively without interference from moisture or other contaminants.

Here is a breakdown of why this is important:

Sensitivity of Grignard Reagents: Grignard reagents are highly reactive organometallic compounds. They are sensitive to moisture because they react with water to form alkanes and magnesium hydroxide, thereby destroying the Grignard reagent.
Importance of Dryness:
- Water: Even a small amount of residual water can quench Grignard reagents, rendering them ineffective for the intended reaction.
- Acetone: While acetone is generally used as a drying agent, any acetone remaining in the glassware can also react negatively. It can react with Grignard reagents to form tertiary alcohols, which might interfere with the intended reaction products.
Cleaning Procedure:
- The glassware is washed with water to remove any water-soluble impurities.
- It is then rinsed with acetone, which helps to remove any remaining water by mixing with it and evaporating easily.
- Finally, the glassware is dried thoroughly, often with heat or by using a drying oven, to ensure no water or acetone remnants are present.

Therefore, the correct choice for why glassware must be completely dry in a Grignard reaction is: "If the glassware is not completely dry, residual water or acetone will react with the Grignard reagent."

Taking these precautions ensures that the delicate Grignard reaction proceeds without adverse interference, leading to successful chemical synthesis.