NMR Determination of Hydrogen Bond Thermodynamics in a Simple Diamide: A Physical Chemistry Experiment
-
Janine G. Morton [1] ; Candice L. Joe [1] ; Massiel C. Stolla [1] ; Sophia R. Koshland [1] ; Casey H. Londergan [1] ; Mark H. Schofield [1]
-
[1] Haverford College
Haverford College
City of Philadelphia, Estados Unidos
-
- Localización: Journal of chemical education, ISSN 0021-9584, Vol. 92, Nº 6, 2015, págs. 1086-1090
- Idioma: inglés
- Texto completo no disponible (Saber más ...)
-
Resumen
Variable temperature NMR spectroscopy is used to determine the ΔH° and ΔS° of hydrogen bond formation in a simple diamide. In this two- or three-day experiment, students synthesize N,N′-dimethylmalonamide, dimethylsuccinamide, dimethylglutaramide, or dimethyladipamide from methylamine and the corresponding diester (typically in 50% recrystallized yield) and record NMR spectra at temperatures between 200 and 313 K. Solutions of N-methylacetamide in concentrations between 1.00 mM and 13.1 M (neat) are prepared and their NMR spectra recorded to determine the chemical shift of the amide proton in the hydrogen-bonded (δB) and nonbonded (δN) limits. By using these data, the equilibrium constants, ΔH°, and ΔS° for the conversion of an open-chain diamide to a cyclic structure with an intramolecular hydrogen bond are determined.
