Thermochemical
properties and intramolecular interactions of 2,2′-dinitrodiphenyl
disulfide (2DNDPDS) and 4,4′-dinitrodiphenyl disulfide (4DNDPDS)
were determined and analyzed. Their standard molar formation enthalpies
in the gas phase (ΔfHm°(g)’s)
were experimentally determined; theoretically, they were computed
using the G4 composite method and atomization reactions. Specifically,
ΔfHm°(g)’s were obtained by combining
formation enthalpies in the condensed phase and enthalpies of phase
change. Formation enthalpies in the condensed phase were determined
experimentally through combustion energies, which in turn were found
by means of a rotatory bomb combustion calorimeter. Sublimation enthalpies
were derived from thermogravimetric experiments, measuring the rate
of mass loss and using Langmuir and Clausius–Clapeyron equations.
Fusion enthalpies and heat capacities of the solid and liquid phases
were measured as functions of temperature by differential scanning
calorimetry, and the heat capacities of the gas phase were calculated
via molecular orbital calculations. Theoretical and experimental ΔfHm°(g)’s differed by <5.5kJ·mol–1, and isomerization enthalpies are discussed. In addition,
using theoretical tools [natural bond orbitals (NBO) and quantum theory
of atoms in molecules (QTAIM)], intramolecular interactions were analyzed.
An uncommon hypervalent four-center six-electron interaction of type
O···S–S···O was found in 2DNDPDS.
This hypervalent interaction, in addition to the extent of conjugation
between the aryl and NO2moieties and the formation of
intramolecular C–H···S hydrogen bonds, counteracts
the repulsion caused by steric repulsions. Hydrogen bonding was confirmed
through geometric parameters as well as QTAIM.