A Level Chemistry OCR Practice Exam

What occurs during nucleophilic substitution?

1. A nucleophile loses electrons

2. A nucleophile is attracted to a positive center and donates a pair of electrons

3. A nucleophile forms a bond with a metal

4. A nucleophile exchanges atoms with another nucleophile

The correct answer is: A nucleophile is attracted to a positive center and donates a pair of electrons

During nucleophilic substitution, a nucleophile is attracted to a positively charged or electron-deficient center within a substrate, such as in alkyl halides. The nucleophile, which is a species with a lone pair of electrons or a negative charge, donates a pair of electrons to form a new bond with the electrophile at that center. This process typically involves the displacement of a leaving group, which was previously bonded to the substrate. As the nucleophile donates its electron pair to the electrophile, the leaving group is expelled, resulting in the substitution of one group for another. The other options do not represent the mechanics of nucleophilic substitution accurately. For example, the idea that a nucleophile loses electrons contradicts its role as an electron donor in these reactions. A nucleophile forming a bond with a metal does not correctly describe the typical context of nucleophilic substitution, which generally involves organic substrates rather than metals. Lastly, the concept of a nucleophile exchanging atoms with another nucleophile misrepresents the fundamental process, which focuses on the nucleophile attacking the electrophile rather than interacting with another nucleophile. Thus, the correct understanding of how nucleophilic substitution occurs is centered on the nucleophile donating a pair of