The Grignard Experiment: The Principles Of Organometallic Chemistry

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This experiment was performed in order to prepare the Grignard reagent from aryl or alkyl halides and demonstrate the principles of organometallic chemistry. The Grignard reagent was prepared via a radical mechanism. The Grignard reagent was then used to prepare a carboxylic acid from carbon dioxide, demonstrating its ability to create carbon-carbon bonds by acting as a strong nucleophile. As the R group of the Grignard reagent was unknown, molecular weight and melting point were then used to identify the resulting carboxylic acid. The molecular weight was determined using titration techniques and the melting point was measured using a Mel-Temp Apparatus.

Data and Results In the formation of the Grignard reaction, the solution turned cloudy and bubbled and then turned to a darker brown color. The mass of the product was measured to be 0.588g. The melting point of the product was between 119C and 121C.
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The magnesium metal attacks the halide creating a radical alkyl product and a radical magnesium atom in association with the halide. The two radicals then combine to form R-MgX. Due to the difference in electronegativity between the carbon and the magnesium atom that are bound together, there is strong polarization and the carbon atom possesses a partial negative charge. This negative charge turns the carbon into a nucleophile, which allows it to attack electrophilic carbons to form new carbon-carbon bonds. The formation of these bonds happens through the following mechanism, given carbon dioxide as a reactant for example. The nucleophilic, negative carbon in the Grignard reagent attacks the electrophilic carbon in carbon dioxide and the electrons in one of the double bonds move to the oxygen atom. This creates a new carbon-carbon bond between them and leaves the MgBr. Then water is added in order to protonate the negatively charged oxygen atom to create a carboxylic

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