A post-Hartree-Fock quantum chemical investigation of biuret planarity

Jabalameli, Ali; Nowek, Andrzej; Hart, Omega; Sullivan, Richard H.; Leszczyński, Jerzy

doi:10.1016/s0166-1280(97)00213-3

Cited by 6 publications

(7 citation statements)

References 24 publications

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“…25 Furthermore, computational studies of biuret found that real frequencies were predicted only for nonplanar forms of biuret, although the energies of the planar and nonplanar forms are very similar. 27 This result rules out the C 2v (for cis) and the C s space groups for the symmetry of biuret molecule. While it is possible that the cis belongs to C 2 point group, it seems most likely that the isolated biuret molecules have C 1 symmetry, regardless of whether they are cis or trans.…”

Section: ■ Results and Discussionmentioning

confidence: 66%

Hydrogen-Bonding Modification in Biuret Under Pressure

Borstad

2017

J. Phys. Chem. A

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Biuret (CHNO) has been studied to 30 GPa by Raman spectroscopy and 50 GPa by X-ray diffraction. Raman peaks exhibit shoulders and splitting that suggests that the molecules undergo reorientation in response to compression. These are observed in three pressure ranges: the first from 3-5 GPa, the second from 8-12 GPa, and finally from 16-20 GPa. The particular modes in the sample that are observed to change in the Raman are strongly linked to the molecular vibrations involving the N-H and the C═O bond, which are most strongly coupled to the hydrogen-bonded lattice structure. The X-ray diffraction suggests that the crystal maintains a monoclinic structure to the highest pressures studied. Although there was a considerable degree of hysteresis observed in some X-ray runs, all the changes observed under pressure are reversible.

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Section: ■ Results and Discussionmentioning

confidence: 66%

Hydrogen-Bonding Modification in Biuret Under Pressure

Borstad

2017

J. Phys. Chem. A

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“…ZPE corrected energy values and relative energy values (at HF, B3LYP, and MP2(full) levels) of tautomers of these compounds are given as supplementary information in S1–S6. Isomers 1a – 4a are almost planar molecules, with little nonplanarity arising due to the partial pyramidal character at N3 and N7 21. These isomers are also characterized by intramolecular hydrogen bond (X1… H8), electron delocalization from lone pair electrons on N3, N4, and N7 to the π frame of the isomer.…”

Section: Resultsmentioning

confidence: 99%

“…According to the general formula reported in literature, diketo form (H 2 NCXNHCYNH 2 ; X = O, Y = O, biuret; X = Y = S, dithiobiuret; and X = O, Y = S, thiobiuret), these group of compounds have two amide ( 1a ), two thioamide groups ( 2a ), one amide and one thioamide groups ( 3a and 4a ) bridged by NH group 2, 4, 5, 20, 21 (Scheme ). On the basis of their molecular formula, one would expect a facile tautomerization that involves transfer of hydrogen atom from the central N atom to the adjacent carbonyl (thiocarbonyl) groups resulting in several possible tautomers.…”

Section: Introductionmentioning

confidence: 99%

“…These systems are generally written as I 1,3 but they are not expected to be stable in this conformation because of severe lone pair electron repulsion. Electronic structure analysis clearly indicated that conformer II to be more appropriate representation of these systems 20, 21 (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

“… The reported most stable structures to represent biuret ( 1a ), dithiobiuret ( 2a ), and two isomers of thiobiuret ( 3a, 4a ) 2, 4, 5, 20, 21. …”

Section: Introductionmentioning

confidence: 99%

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Tautomeric preferences and electron delocalization in biurets, thiobiurets, and dithiobiurets: Anab initiostudy

Adane¹,

Bharatam²

2008

Int J of Quantum Chemistry

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ABSTRACT:In several literature reports biuret and its sulfur analogs are reported to exist in their diketo form with general formula H 2 NOCXONHOCYONH 2 (X ϭ O, Y ϭ O, biuret; X ϭ Y ϭ S, dithiobiuret; and X ϭ O, Y ϭ S, thiobiuret). On the other hand, recently reported results on the electronic structure of biguanide analogs (X ϭ Y ϭ NH) demonstrated that a form equivalent to diketo is not the preferred structure. Thus, a systematic ab initio study on the tautomeric preferences of biuret and its sulfur analogs (dithiobiuret and thiobiuret) has been carried out. The results indicate that an interplay of conjugative stabilization and intramolecular hydrogen bonding to play a role in tautomeric preferences. Energy and geometric parameters, natural bond orbital analyses have been employed to understand the chemistry of the title compounds. The results indicate that unlike biguanides, these compounds prefer diketo forms containing hydrogen on the bridging nitrogen (N4) and in a trans-arrangement (1a-4a). However, tautomerization of these keto forms to the corresponding enol isomers was also found to be highly probable.

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