Reactions of molecules with two equivalent functional groups. 3. Nucleophilic substitution reactions of α, ω‐dibromoalkanes [Br(CH 2 ) n Br, n = 3,4,5] with potassium cyanide

The substitution reactions of Br(CH 2 ) n Br(1, n = 3–5) with KCN in methanol were studied in detail. Second‐order rate constants k 1 [formation of the mononitrile (2) from 1] and k 2 (formation of the dinitrile (3) from 2) were determined, as were the rates for the reaction of H(CH 2 ) n Br (4, n = 3‐5) with KCN under the same conditions. The ratios k 2 / k 1 ( = x ) of the three homologs of 1 were found to be 1.15, 0.77 and 0.61 for n = 3, 4 and 5, respectively; a x value of 0.5 indicates that the functional groups behave independently. The second‐order rate constants k 1 (statistically corrected) and k 2 exhibit modest enhancements compared with model compound 4 when any of the following substituents are present: δ or ϵ‐bromo, γ‐, δ‐, or ϵ‐cyano. By contrast, a γ‐bromo substituent slightly retards the rate. These results indicate that the functional groups do influence each other to a modest degree by field effects which accelerate the reactions. Steric effects do not appear to play a significant role.