A Level Chemistry OCR Practice Exam

A nucleophile participates in a chemical reaction primarily when it is attracted to an electron-deficient center. Nucleophiles are species that donate an electron pair to an electrophile, which is an atom or group that is electron-deficient and thus seeks to obtain electrons. This attraction drives the nucleophilic attack, resulting in the formation of new chemical bonds.

In this context, the nucleophile approaches the electrophile due to the presence of a partial positive charge or an overall positive charge on the electron-deficient center, making it more susceptible to the attack of the nucleophile. This interaction is a fundamental aspect of many reaction mechanisms, including substitution and addition reactions in organic chemistry.

While exposure to a metal may influence the reactivity of nucleophiles, it isn't a necessary condition for their participation in reactions. Encountering an electron-rich atom does not provide the necessary condition for nucleophiles, as they seek to bond with electron-deficient entities. Regarding the reaction between two nucleophiles, this is not typical, as they both carry a negative charge and would generally repel each other rather than bond. Thus, the attraction to an electron-deficient center accurately characterizes when nucleophiles actively engage in chemical reactions.