Isomerism in the diphosphirane series

The cis/trans stereochemistry of diphosphiranes 1a–g, 2a, and 2h is investigated by MNDO calculations in terms of substituent effects on intracyclic phosphorus and carbon atoms. This approach is completed by calculations of dipole moments. These results are compared to experimental dipole moment measurements of the synthesized diphosphiranes 3a–f.

Dipole moment of the charge transfer complex 1-ethyl-4-methoxy carbonyl pyridinium iodide

Dipole moment of a biologically important model compound: Charge transfer complex 1-ethyl-4-methoxy carbonyl pyridinium iodide was determined experimentally. A three component method was employed for this purpose, which is especially useful for determining the dipole moment of a salt insoluble in nonpolar solvents. The experimental dipole moment of this compound, hitherto unmeasured, was found to be (37.7 ± 1.0) . 10-30 C m against the theoretical (contact) ion pair value of 46.4 . 10-30 C m.

Thermodynamic Properties of Refrigerant-Absorbent Pairs

An analytical method has been proposed to calculate thermodynamic properties of refrigerant-absorbent mixtures of polar molecules. The critical pressure, critical temperature, critical volume and experimental dipole moment of pure components are required in the proposed method. The calculated properties have been compared with the available experimental data and results reported in the literature. The comparison shows very good agreement. Thus, this method is recommended for use with refrigerant-absorbent pairs having polar molecules.

Dipole moment of the intramolecular hydrogen bond. 2-Nitrophenol and its derivatives

Dipole moments of substituted 2-nitrophenols VIa-VIf and substituted 2-nitroanisoles VIIa to VIIf were measured in benzene and dioxan solutions. Infrared spectroscopy confirmed that nitrophenols VI exist either solvent and at different concentrations as non-associated molecules with an intramolecular hydrogen bond. Therefore, the difference between the experimental dipole moment and that calculated from group moments can be attributed to charge redistribution raised by the hydrogen bond. Only a minute part of it may be due to electron transfer through the ring (conjugation of the functional groups) as follows particularly from he comparison with nitroanisoles VII. Nevertheless, the charge transfer, expressed as the vector μH, amounts only 1.7 . 10-30 Cm (at an angle of 138° to the H-O bond), i.e. several times less than observed previously in compounds with more powerful hydrogen acceptors. CNDO/2 and MNDO calculations agree fairly with the gross dipole moments of the compounds investigated but are unable to predict μH, not even as far as its direction is concerned.