Intramolecular hydrogen bonding in N-salicylideneanilines. X-ray diffraction and solid-state NMR studies

A new polymorph of 2,4-dihydroxybenzoic acid is reported. The structure was characterized by multiple-temperature X-ray diffraction and solid-state DFT computations. The material shows a geometric pattern of hydrogen bonding consistent with cooperativity between the intermolecular carboxylic acid dimer and intramolecular hydrogen bonds. The presence of proton disorder within this hydrogen-bond system, which would support such a cooperative model, was not fully ruled out by the initial X-ray studies. However, solid-state calculations on the three possible end-point tautomers indicate that the dominant crystallographically observed configuration is substantially lower in energy than the other tautomers (by at least 9 kJ mol−1), indicating that no disorder should be expected. It is therefore concluded that no disorder is observed either in the intra- or intermolecular hydrogen bonds of the title compound and that the cooperativity between the hydrogen bonds is not present within the temperature range studied.

Download Full-text

Tetra(alkynyl)silanes, a 3,6-Disila-triyne, a 3,6,9-Trisila-tetrayne, a 1,3,4,6-Tetrasiladiyne, and Bis(trimethylstannyl)ethyne. Molecular Structures and Solid-state NMR Studies

Zeitschrift für Naturforschung B ◽

10.1515/znb-2010-0204 ◽

2010 ◽

Vol 65 (2) ◽

pp. 119-127 ◽

Cited By ~ 8

Author(s):

Bernd Wrackmeyer ◽

Ezzat Khan ◽

Amin Badshah ◽

Elias Molla ◽

Peter Thoma ◽

...

Keyword(s):

Solid State ◽

Nmr Spectroscopy ◽

Solid State Nmr ◽

Mas Nmr ◽

Molecular Structures ◽

X Ray Diffraction ◽

Nmr Studies ◽

X Ray ◽

Solution State ◽

Nmr Data

The molecular structures of three alkynylsilanes, tetrakis(ethynyl-p-tolyl)silane, 3,3,6,6,-tetramethyl- 3,6-disila-triyne, 3,3,6,6,9,9,-hexamethyl-3,6,9-trisila-tetrayne, and of bis(trimethylstannyl)- ethyne have been determined by X-ray diffraction. The same alkynylsilanes, and in addition 1,2- bis(trimethylsilylethynyl)-1,1,2,2-tetramethyldisliane, were studied by solid-state 13C and 29Si MAS NMR spectroscopy. The results of these measurements were compared with crystallographic evidence and also with relevant solution-state NMR data.

Download Full-text

13C CP/MAS NMR spectra of poly-β-D(1 → 4) mannose: mannan

Canadian Journal of Chemistry ◽

10.1139/v90-184 ◽

1990 ◽

Vol 68 (7) ◽

pp. 1192-1195 ◽

Cited By ~ 15

Author(s):

R. H. Marchessault ◽

M. G. Taylor ◽

W. T. Winter

Keyword(s):

Hydrogen Bonding ◽

Solid State ◽

Solid State Nmr ◽

Nmr Spectra ◽

Repeat Unit ◽

Intramolecular Hydrogen Bonding ◽

Lower Mobility ◽

Intramolecular Hydrogen ◽

Cp Mas Nmr ◽

13C Cp Mas Nmr

13C solid-state NMR spectra (CP/MAS) were recorded for mannan polymorphs: mannan I ("ivory nut") and mannan II (Codiumfragile). These pure mannans, poly-β-(1 → 4) mannopyranose, show a single resonance for each carbon of the chemical repeat unit. This is the expected result based on the crystalline P212121 and 1222 symmetries. The T1 values were also recorded and the results are compared to those for cellulose obtained from the literature. The much lower mobility of C-6, even in noncrystalline mannan, compared to native cellulose is attributed to the epimeric difference at C-2 between cellulose and mannan allowing intramolecular hydrogen bonding in the former but not the latter. Keywords: mannan, solid state NMR, T1 relaxation, polysaccharide, ivory nut.

Download Full-text