Entropy-driven hydrogen bonding: Stereodynamics of a protonated, N,N-chiral "proton sponge"

P Hodgson, GC Lloyd-Jones*, M Murray, TM Peakman, RL Woodward

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The C-2-symmetric ("[DL]") and achiral ("[meso]") diastereoisomers of the hydrogen iodide salt of 1,8-bis-(N-benzyl-N-methylamino)naphthalene ([2H](+)[I](-)) interconvert in solution. Direct interconversion of the diastereoisomers of [2H](+) must involve hydrogen bond fission (to give "[nonHB-2H(+)]'') and rotation-inversion of the non-protonated nitrogen centre. The global activation parameters (DeltaH(not equal) and DeltaS(not equal)) for diastereoisomer interconversion in [D-7]DMF have been determined from rate data obtained by temperature-drop and magnetisation-transfer C-13 NMR spectroscopy over a temperature range of 170 degreesC. The process is found to have a high entropy of activation in both directions (DeltaS(not equal) = 163(+/-4) and 169(+/-4) J K-1 mol(-1)) and this is suggested to arise through hydrogen bonding of the ammonium centre in [nonHB-2H(+)] with the solvent ([D-7]DMF). Comparison of the enthalpy of activation (DeltaH(not equal)) with that earlier found for diastereoisomer interconversion of the free-base form 2 suggests that the intramolecular hydrogen bond in [2H](+) is roughly equal in enthalpic strength (DeltaH) with that made with the solvent ([D-7]DMF) in the non-hydrogen-bonded intermediate [nonHB-2H(+)]. As such, the hydrogen bonding in [2H](+) may be considered as predominantly an entropically driven process, without any unusual enthalpic strength.

Original languageEnglish
Pages (from-to)4451-4460
Number of pages10
JournalChemistry - A European Journal
Volume6
Issue number24
Publication statusPublished - 15 Dec 2000

Keywords / Materials (for Non-textual outputs)

  • hydrogen bonds
  • isotopic labeling
  • NMR spectroscopy
  • proton sponges
  • stereodynamics
  • ENZYMATIC CATALYSIS
  • BONDED ACIDS
  • AB-INITIO
  • NMR
  • 1,8-BIS(DIETHYLAMINO)-2,7-DIMETHOXYNAPHTHALENE
  • 1,8-BIS(DIMETHYLAMINO)NAPHTHALENE
  • DIFFRACTION
  • BASICITIES
  • MECHANISM
  • STRENGTH

Fingerprint

Dive into the research topics of 'Entropy-driven hydrogen bonding: Stereodynamics of a protonated, N,N-chiral "proton sponge"'. Together they form a unique fingerprint.

Cite this