Skip to main content
eScholarship
Open Access Publications from the University of California

The basicity of unsaturated hydrocarbons as probed by hydrogen-bond- acceptor ability: Bifurcated N-H+⋯μ hydrogen bonding

  • Author(s): Stoyanov, ES
  • Stoyanova, IV
  • Reed, CA
  • et al.
Abstract

The competitive substitution of the anion (A-) in contact ion pairs of the type [Oct3NH+]B(C6F5V by unsaturated hydrocarbons (L) in accordance with the equilibrium Oct 3NH+ ⋯A- + nL ⇄ [Oct 3NH+-Ln]A- has been studied in CCl4. On the basis of equilibrium constants, K, and shifts of vNH to low frequency, it has been established that complexed Oct3NH +-L., cations with n = 1 and 2 are formed and have unidentate and bifurcated N-H+⋯μ hydrogen bonds, respectively. Bifurcated hydrogen bonds to unsaturated hydrocarbons have not been observed previously. The unsaturated hydrocarbons studied include benzene and methylbenzenes, fused-ring aromatics, alkenes, conjugated dienes, and alkynes. From the magnitude of the redshifts in the N-H stretching frequencies, AvNH, a new scale for ranking the It basicity of unsaturated hydrocarbons is proposed: fused-ring aromatics ≤ benzene < toluene < xylene < mesitylene < durene < conjugated dienes ≈ 1 -alkynes < pentamethylbenzene < hexamethylbenzene < internal alkynes ≈ cycloalkenes < 1 -methylcycloalkenes. This scale is relevant to the discussion of It complexes for incipient protonation reactions and to understanding N-H+⋯ μ hydrogen bonding in proteins and molecular crystals. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Many UC-authored scholarly publications are freely available on this site because of the UC Academic Senate's Open Access Policy. Let us know how this access is important for you.

Main Content
Current View