Ion chemistry of cyanides and isocyanides. 1. The carbon lone pair as proton acceptor: proton affinities of isocyanides. Alkyl cation affinities of N, O, and C lone-pair donors

Journal Article · Wed Jul 09 04:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00274a010· OSTI ID:5583628

Meot-Ner, M ^[1]; Karpas, Z; Deakyne, C A

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1. Mautner

The proton affinities (PAs) of the isocyanides RNC, R = CH/sub 3/, C/sub 2/H/sub 5/, i-C/sub 3/H/sub 7/, t-C/sub 4/H/sub 9/, and C/sub 6/H/sub 5/, range from 199 to 207 kcal/mol. The PAs of all the isocyanides are higher than those of the corresponding cyanides, RCN, by a constant 11.5 +/- 1 kcal/mol, regardless of the identity of R. The isomerization energies of the RNCH/sup +/ ions to RCNH/sup +/ are 5-11 kcal/mol and are smaller by 11-15 kcal/mol than the isomerization energies of the respective neutral cyanides. The bond dissociation energies D/sup 0/ for R/sup +/-NCH, R/sup +/-CNH, R/sup +/-OH/sub 2/, and R/sup +/-NH/sub 3/ show unexpectedly good linear correlations with the stabilities of the R/sup +/ ions as measured by the hydride affinity, i.e., D/sup 0/ (R/sup +/-H/sup -/). Ab initio calculations are used to analyze the trends in proton affinities. The results show that the main structural effects of protonation on RNC are the shortening of the N-C and the lengthening of the R-N bonds. The calculations also suggest that the larger PAs of RNC vs. RCN arise primarily from larger charge transfer and electrostatic interactions in the isocyanides. However, the parallel increase of the PAs of both RCN and RNC as R gets bigger is due primarily to the increasing polarizabilities of the substituents.

• Research Organization: National Bureau of Standards, Gaithersburg, MD
• OSTI ID: 5583628
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:14; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
640105 -- Astrophysics & Cosmology-- Galaxies
640107 -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
DATA
ESTERS
EXPERIMENTAL DATA
HYDROGEN TRANSFER
INFORMATION
IONS
ISOCYANIC ACID ESTERS
MOLECULAR ORBITAL METHOD
NUMERICAL DATA
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
STRUCTURAL CHEMICAL ANALYSIS
THERMODYNAMIC PROPERTIES