See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents (RMgX) are highly reactive organomagnesium compounds that require solvents capable of stabilizing (solvating) the magnesium center through lone pair donation. Suitable solvents must have lone pairs available for coordination to Mg but must lack any acidic protons or electrophilic sites that would destroy the Grignard reagent. Step 1 - Identify what makes a good Grignard solvent: The solvent must be able to coordinate to the Mg atom via lone pairs on oxygen (or nitrogen), thereby stabilizing the Grignard reagent. Ethers are the classic solvents because their oxygen lone pairs coordinate to Mg without reacting destructively. The solvent must also be aprotic. Step 2 - Evaluate each option: (a) THF (tetrahydrofuran): A cyclic ether with an oxygen atom bearing lone pairs. It coordinates well to Mg and is the most commonly used solvent for Grignard reactions. SUITABLE. (b) 1,4-Dioxane: A cyclic diether with two oxygen atoms. It has lone pairs on both oxygens. It can solvate Mg and has been used as a co-solvent or solvent in Grignard chemistry. SUITABLE (though less commonly used alone, it is not 'not suitable' in the same absolute sense as cyclohexane). (c) CH3-O-CH2-CH2-O-CH3 (1,2-dimethoxyethane, DME/glyme): A diether with two oxygen atoms that chelate Mg very effectively. It is an excellent solvent for Grignard reactions. SUITABLE. (d) Cyclohexane: A simple cycloalkane with no heteroatoms, no lone pairs, and therefore no ability to coordinate to or solvate the magnesium center of the Grignard reagent. Without solvation by a Lewis basic solvent, the Grignard reagent cannot form or remain stable. Cyclohexane is a non-polar, non-coordinating hydrocarbon solvent entirely unsuitable for Grignard reactions. Step 3 - Conclusion: Options (a), (b), and (c) are all ethers capable of donating lone pairs to stabilize the Grignard reagent. Option (d), cyclohexane, has no oxygen or other heteroatom and cannot solvate the Grignard reagent, making it completely unsuitable. Therefore, the correct answer is D.