AbstractThe reactions of cycloalkyl (butyl, pentyl, hexyl and heptyl) chlorides and bromides with diphenylphosphide ions were studied in liquid ammonia. Cyclobutyl chloride was unreactive, whereas the bromide reacted giving the substitution product cyclobutyldiphenylphosphine (isolated as the oxide) in good yields; this reaction was catalysed by light and partially inhibited byp‐dinitrobenzene (p‐DNB). Cyclopentyl, cyclohexyl and cycloheptyl chlorides did not react in the dark, but the substitution products were formed under irradiation, and these reactions were inhibited byp‐DNB. The bromides reacted in the dark or under irradiation, and these reactions were partially inhibited byp‐DNB. It can be then concluded that the reactivity of cycloalkyl halides depends on the ring size and the nucleofugal group. In addition, as the overall reactivity decreases, there is an increase in electron transfer re