Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-2234
    Keywords: Nitramines ; Vibrational analysis ; Thermal decomposition ; Activation energies ; Dissociation energies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have investigated some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative, the latter being selected as the simplest example of a symmetric cyclic nitramine. Vibrational analyses were used to identify normal modes that, in the extreme limits, would correspond to bond rupture and molecular decomposition. The energy requirements for ring fragmentation and N-N bond-breaking were computed at the MP4/6-31G level, using SCF 3-21G optimized structures. It was concluded that ring-fragmentation is a probable initiating step in the decomposition of the unsubstituted molecule, and that it is roughly competitive with N-N bond scission for the dinitramine. The nitronitrite rearrangement is predicted, on the basis of SCF calculations, to be less likely than either of the other two processes. It is proposed that N-N bond-breaking may be of primary importance for nitramine stability, but that energetic performance may be determined more by decomposition pathways having energy barriers.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1572-8951
    Keywords: Diaryl ureas ; electrostatic potentials ; hydrogen bond patterns ; cocrystal selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have carried out anab initio self-consistent-field molecular orbital analysis of the structures, atomic charges and electrostatic potentials of 1,3-bisphenylurea, 1,3-bis(m-nitrophenyl)urea and 1,3-bis(p-nitrophenyl)urea. Our results provide insight into the contrasting hydrogen bond patterns and preferences of these molecules in crystalline environments. The tendency for 1,3-bisphenylurea to form homomeric rather than heteromeric (i.e. host-guest) crystals is attributed to a relatively strong and extended homomeric attractive electrostatic interaction between two like molecules. Our calculated internuclear distances and atomic charges indicate that these molecules have some degree of H...O intramolecular hydrogen bonding between the carbonyl oxygen and the nearest aromatic hydrogens when the aromatic and the urea portions of the molecules are coplanar. This interaction is strongest for the meta nitro derivative, consistent with the latter remaining very nearly planar in its cocrystal structures. Our surface electrostatic potentials for the three diaryl ureas are used to interpret their differing crystallization properties and tendencies to form cocrystals with guest molecules.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...