Reduced Nucleophilicities И B of Lewis Bases B: Is И B Independent of Whether B is Involved in a Hydrogen Bond or a Halogen Bond?

Reduced nucleophilicities И B of axially symmetric molecules B were determined from , where D e is the equilibrium dissociation energy of the complexes B⋅⋅⋅XY, N B is the nucleophilicity of B, E XY is the electrophilicity of the halogen-bond donor XY and σ min ${{\sigma }_{{\rm { min}}}{\rm \ }}$ is the minimum electrostatic surface potential of B. The series B⋅⋅⋅ClY, B⋅⋅⋅BrY, B⋅⋅⋅IY (Y=F, Cl, Br, I, CN, and CCH) as well as (B⋅⋅⋅XY, XY=F 2 , Cl 2 , Br 2 ,and BrCl) of complexes were investigated. Molecules B were grouped so that the terminal atom involved in the halogen bond was fixed within the group. Groups having N as the terminal atom were RCN (R=CH 3 , H, and F) or RN (R=N and P), those with C as the terminal atom were RNC (R=H and F) and RC (R=O, S and Se), and those with a terminal O atom were R=C=O (R=O or S). Graphs of D e ${{D}_{{\rm { e}}}}$ versus E XY for each group were straight lines through the origin, with generally different gradients, hence implying different N B . By contrast, when D e / σ min ${{D}_{{\rm { e}}}/{\sigma }_{{\rm { min}}}}$ was the ordinate the lines conflated to give a single straight line, which then defines a common (reduced) nucleophilicity И B for that group of B. Hence it was concluded that И B is an intrinsic property of the terminal atom, independent of the remainder of B, and only weakly dependent on the type (C, N or O) of the terminal atom. Moreover, И B for each B was the same as determined previously from the hydrogen-bonded series B⋅⋅⋅HX, (X=F, Cl, Br, I, CN, CCH, and CP).