ChemInform Abstract: Conformational Properties of Carbonyl Isocyanates - Stereoelectronic Effects Favoring the Cisoid Conformation

ChemInform ◽  
2010 ◽  
Vol 25 (3) ◽  
pp. no-no
Author(s):  
D. KLAPSTEIN ◽  
W. M. NAU
Keyword(s):  
Stereoelectronic Effects ◽  
Conformational Properties

A Computational Study of the Conformational Behavior of 2,5-Dimethyl- 1,4-dithiane-2,5-diol and Analogous S and Se: DFT and NBO Study

2020 ◽  
Vol 17 (10) ◽  
pp. 749-759
Author(s):  
Elmira Danaie ◽  
Shiva Masoudi ◽  
Nasrin Masnabadi
Keyword(s):  
Thermodynamic Parameters ◽  
Computational Study ◽  
Structural Parameters ◽  
Nbo Analysis ◽  
Electron Delocalization ◽  
Stereoelectronic Effects ◽  
Conformational Properties ◽  
Molecular Reactivity ◽  
Stabilization Energies ◽  
The Stability

Conformational behaviors of 2,5-dimethyl-1,4-dithiane-2,5-diol (compound 1), 2,5- dimethyl-1,4-dithiane-2,5-dithiol (compound 2) and 2,5-dimethyl-1,4-dithiane-2,5-diselenol (compound 3) were investigated by the B3LYP/6-311+G **, the M06-2X/aug-ccpvdz levels of theory and natural bond orbital NBO analysis. The structures and the structural parameters of the mentioned molecules were optimized by the B3LYP and the M06-2X methods. We assessed the roles and contributions of the effective factors in the conformational properties of the mentioned compounds by means of the B3LYP and M06-2X levels of theory and the NBO interpretations. The stereoelectronic effects of the mentioned molecules were studied using the NBO analysis. The results showed that the stereoelectronic effects were in favor of the (ax,ax) conformers (the most stable conformations), from compound 1 to compound 3; therefore, these effects have impacts on the conformational properties of compounds 1-3, and stabilization energies associated with LP2X→ σ*S1-C2 electron delocalization, where [X= O, S, and Se], for 1-ax, ax conformer has the greatest value between all of the other conformers. Therefore, according to the calculated thermodynamic parameters, the stability of the 1-ax, ax compound was justified by the presence of LP2X→σ*S1-C2 electron delocalization. A molecular orbital explanation was conducted to investigate the correlations between the linear combinations of natural bond orbitals in the HOMOs, LUMOs and the molecular reactivity parameters. There is a direct relationship between the stereoelectronic effects, molecular reactivity and thermodynamic parameters of compounds 1 to 3 as the harder ax, ax conformations with the greater stereoelectronic effects and ΔG(eq-ax) values are more stable than their corresponding eq, eq conformers. Besides frontier molecular orbitals (FMOs), mapped molecular electrostatic potential (MEP) surfaces of conformations of compounds 1 to 3 were investigated.

The conformational properties of calix[4]arenes 1h NMR and molecular mechanics calculations

1989 ◽  
Vol 86 ◽  
pp. 945-954 ◽  
Author(s):  
F. Bayard ◽  
D. Decoret ◽  
D. Pattou ◽  
J. Royer ◽  
A. Satrallah ◽  
...  
Keyword(s):  
Molecular Mechanics ◽  
1H Nmr ◽  
Molecular Mechanics Calculations ◽  
Conformational Properties

Effect of temperature on chiroptical and conformational properties of acyclic ketoses

1980 ◽  
Vol 45 (2) ◽  
pp. 475-481
Author(s):  
Slavomír Bystrický ◽  
Tibor Sticzay ◽  
Igor Tvaroška
Keyword(s):  
Quantum Chemical Calculation ◽  
Quantum Chemical ◽  
Conformational Mobility ◽  
Effect Of Temperature ◽  
Chemical Calculation ◽  
Cd Spectra ◽  
Conformational Properties ◽  
Temperature Dependences

Conformational mobility of tetruloses, 2-pentuloses, D-3-pentulose and 4-deoxy-L-pentulose was studied by measuring temperature dependences of CD spectra in the region +40°C to -140°C in a methanol-ethanol (1:4) mixture. The changes in spectra reflect the population of rotamers around bonds to the carbonyl chromophore. The most stable conformers were determined by PCILO quantum chemical calculation.

Conformational study on ribonucleoside O-phosphonylmethyl derivatives by 1H NMR spectroscopy

1985 ◽  
Vol 50 (8) ◽  
pp. 1899-1905 ◽  
Author(s):  
Milena Masojídková ◽  
Jaroslav Zajíček ◽  
Miloš Buděšínský ◽  
Ivan Rosenberg ◽  
Antonín Holý
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Conformational Study ◽  
H Nmr ◽  
Conformational Properties

Conformational properties of ribonucleoside 5'-O-phosphonylmethyl derivatives have been determined by 1H NMR spectroscopy and compared with those of natural nucleosides and 5'-nucleotides.

1H NMR studies of [N-MeAib1, Tyr(Me)4]ANGII and [N-MeAib1, Tyr(Me)4, Ile8]ANGII in dimethylsulfoxide by nuclear Overhauser effect (NOE) enhancement spectroscopy: cis-trans Isomerism of the His-Pro bond

1990 ◽  
Vol 55 (4) ◽  
pp. 1106-1111 ◽  
Author(s):  
John Matsoukas ◽  
Paul Cordopatis ◽  
Raghav Yamdagni ◽  
Graham J. Moore
Keyword(s):  
1H Nmr ◽  
Nuclear Overhauser Effect ◽  
Nmr Studies ◽  
Restricted Rotation ◽  
Overhauser Effect ◽  
Major Isomer ◽  
Conformational Properties ◽  
Nuclear Overhauser

The conformational properties of the Sarmesin analogues [N-MeAib1, Tyr(Me)4]ANGII and [N-MeAib1, Tyr(Me)4, Ile8]ANGII in hexadeutero-dimethysulfoxide were investigated by Nuclear Overhauser Effect (NOE) Enhancement Studies. Cis-trans isomers (ratio 1 : 6) due to restricted rotation of the His-Pro bond were observed. Interresidue interactions between the His Cα proton and the two Pro Cδ protons revealed that the major isomer was the trans.

scholarly journals Spatial segregation of mixed-sized counterions in dendritic polyelectrolytes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
J. S. Kłos ◽  
J. Paturej
Keyword(s):  
Electrostatic Interactions ◽  
Spatial Separation ◽  
Excluded Volume ◽  
The Core ◽  
Bjerrum Length ◽  
Two Component ◽  
Conformational Properties ◽  
Dynamics Simulations ◽  
Two Parameters ◽  
Swelling Factor

AbstractLangevin dynamics simulations are utilized to study the structure of a dendritic polyelectrolyte embedded in two component mixtures comprised of conventional (small) and bulky counterions. We vary two parameters that trigger conformational properties of the dendrimer: the reduced Bjerrum length, $$\lambda _B^*$$ λ B ∗ , which controls the strength of electrostatic interactions and the number fraction of the bulky counterions, $$f_b$$ f b , which impacts on their steric repulsion. We find that the interplay between the electrostatic and the counterion excluded volume interactions affects the swelling behavior of the molecule. As compared to its neutral counterpart, for weak electrostatic couplings the charged dendrimer exists in swollen conformations whose size remains unaffected by $$f_b$$ f b . For intermediate couplings, the absorption of counterions into the pervaded volume of the dendrimer starts to influence its conformation. Here, the swelling factor exhibits a maximum which can be shifted by increasing $$f_b$$ f b . For strong electrostatic couplings the dendrimer deswells correspondingly to $$f_b$$ f b . In this regime a spatial separation of the counterions into core–shell microstructures is observed. The core of the dendrimer cage is preferentially occupied by the conventional ions, whereas its periphery contains the bulky counterions.

scholarly journals AM1 Study of the Conformational Properties of (Z,Z)-Cyclonona-1,3-diene

1999 ◽  
Vol 23 (10) ◽  
pp. 616-617
Author(s):  
Issa Yavari ◽  
Hassan Norouzi-Arasi ◽  
Hossain Fallah-Bagher-Shaidaei
Keyword(s):  
Energy Barrier ◽  
Ring Inversion ◽  
Calculated Energy ◽  
Conformational Properties ◽  
Twist Boat ◽  
Calculated Energy Barrier

The unsymmetrical boat-chair BC conformation of ( Z,Z)-cyclonona-1,3-diene is calculated to be 5 kJ mol−1 more stable than the axial-symmetrical twist-boat-chair TBC form; while the calculated energy barrier for limited pseudorotation of BC and TBC is only 10.2kJ mol−1, ring inversion of BC via plane-symmetrical boat geometry requires 24.4 kJ mol−1.

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