Gas phase basicities of polyfunctional molecules. Part 6: Cyanides and isocyanides.

This paper gathers structural and thermochemical informations related to the gas-phase basicity of molecules containing cyanides (nitriles) and isocyanides (isonitriles) functional groups. It constitutes the sixth part of a general review devoted to gas-phase basicities of polyfunctional compounds. A large corpus of cyanides and isocyanides molecules is examined under seven major chapters. In the first one, a rapid overview of the definitions and methods leading to gas-phase basicity, GB, proton affinity, PA, and protonation entropy, Δp S°, is given. In the same chapter, several aspects of the gas phase chemistry of protonated cyanides and isocyanides are also presented. Chapters II-VI detail the protonation energetics of aliphatic, unsaturated, and heteroatom substituted (halogens, O, S, N, P) cyanides. A seventh chapter is devoted to isocyanides. Experimental data available in the literature (120 references) were reevaluated according to the presently adopted basicity scale that is the NIST database anchored to PA(NH3 ) = 853.6 kJ/mol and GB (NH3 ) = 819 kJ/mol. In this latter source, however, several erroneous values have been identified which were corrected in the present review. Structural and energetic information given by G4MP2 quantum chemistry computations on ca. 60 typical systems are presented. The present review includes the GB, PA, and Δp S° values of ca. 110 cyanides and isocyanides, and, for selected examples, is completed by a set of computed heats of formation (Δf H°) at 0 and 298 K.