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 language | English |
---|---|
Pages (from-to) | 4451-4460 |
Number of pages | 10 |
Journal | Chemistry - A European Journal |
Volume | 6 |
Issue number | 24 |
Publication status | Published - 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