scholarly journals Predicted Reversal in N-Methylazepine/N-Methyl-7-azanorcaradiene Equilibrium upon Formation of Their N-Oxides

Molecules ◽  
2020 ◽  
Vol 25 (20) ◽  
pp. 4767
Author(s):  
René Fournier ◽  
Alexa R. Green ◽  
Arthur Greenberg ◽  
Edward Lee-Ruff ◽  
Joel F. Liebman ◽  
...  
Keyword(s):  
Free Energy ◽  
Chemical Shift ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Basis Sets ◽  
Nucleus Independent Chemical Shift

Density functional calculations and up to five different basis sets have been applied to the exploration of the structural, enthalpy and free energy changes upon conversion of the azepine to the corresponding N-oxide. Although it is well known that azepines are typically much more stable than their 7-azanorcaradiene valence isomers, the stabilities are reversed for the corresponding N-oxides. Structural, thermochemical as well as nucleus-independent chemical shift (NICS) criteria are employed to probe the potential aromaticity, antiaromaticity and nonaromaticity of N-methylazepine, its 7-azanorcaradiene valence isomer. For the sake of comparison, analogous studies are performed on N-methylpyrrole and its N-oxide.

scholarly journals 1,3,5-Triaza-7-Phosphaadamantane (PTA) as a 31P NMR Probe for Organometallic Transition Metal Complexes in Solution

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1390 ◽  
Author(s):  
Ilya G. Shenderovich
Keyword(s):  
Chemical Shift ◽  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Density Functional ◽  
Molecular Structures ◽  
Basis Sets ◽  
Functional Theory ◽  
Non Covalent Interactions ◽  
Covalent Interactions

Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its 31P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this 31P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported.

REEXAMINATION OF LOW ENERGY STRUCTURES OF ${\rm Au}_{4}^{-}$ AND Au4

2010 ◽  
Vol 09 (supp01) ◽  
pp. 1-7 ◽  
Author(s):  
YI GAO ◽  
YU ZHAO ◽  
X. C. ZENG
Keyword(s):  
Free Energy ◽  
Density Functional ◽  
Photoelectron Spectrum ◽  
Global Minimum ◽  
Low Energy ◽  
Basis Sets ◽  
Cluster Method ◽  
Energy Calculation ◽  
Couple Cluster ◽  
B3lyp Method

Low energy isomers of [Formula: see text] and Au4 were reexamined using the hybrid density functional B3LYP method and the couple-cluster method with the aug-cc-pVDZ-PP and aug-cc-pVTZ-PP basis sets. For [Formula: see text], the B3LYP method favors the zigzag isomer and the second order Moller–Plesset perturbation (MP2) total energy calculation favors the D2h rhombus isomer, whereas the couple-cluster singles and doubles with perturbative triples [CCSD(T)] level of theory favors the Y-shaped C2v isomer. The pyramid isomer is much higher in energy and could be easily excluded. The Gibbs free energy correction based on harmonic approximation suggests that the zigzag isomer is lower in free energy than the D2h rhombus isomer at 298.15 K. These results confirm that the Y-shaped C2v isomer is the global minimum at both 0 K and room temperature and is thus the major isomer to account for the experimental photoelectron spectrum. The zigzag isomer is suggested, as a minor isomer, to account for the weak second peak at 3.40 eV in the experimental photoelectron spectrum. For neutral Au4 , the zigzag isomer is more stable than D2h rhombus isomer at the B3LYP level and the D2h rhombus isomer is the global minimum on basis of all post Hartree–Fock levels of theory.

Density functional calculations of Ge(105): Local basis sets andO(N)methods

2007 ◽  
Vol 76 (11) ◽  
Author(s):  
T. Miyazaki ◽  
D. R. Bowler ◽  
R. Choudhury ◽  
M. J. Gillan
Keyword(s):  
Density Functional Calculations ◽  
Density Functional ◽  
Basis Sets ◽  
Local Basis ◽  
Local Basis Sets

Wechselwirkungen in Molekülkristallen, 127 [1] Die unterschiedlichen Strukturen des im Kristall verdrillten 1,4-Bis(tricyanvinyl)- benzols sowie des eingeebneten 1-Tricyanvinylbenzols, Dichtefunktional- Berechnungen und cyclovoltammetrisch sowie ESR/ENDOR-spektroskopisch charakterisiertes Reduktionsverhalten / Interactions in Molecular Crystals, 127 [1]The Different Structures in the Crystal of Twisted 1,4-Bis(tricyanovinyl)benzene as well as of Planar 1-Tricyanovinyl-benzene, Density Functional Calculations and Reduction Behaviour Studied by Cyclovoltammetry and ESR/ENDOR Spectroscopy

1997 ◽  
Vol 52 (9) ◽  
pp. 1125-1138 ◽  
Author(s):  
Hans Bock ◽  
Wolfgang Seitz ◽  
Norbert Nagel ◽  
Rüdiger Baur ◽  
Jan W. Bats ◽  
...  
Keyword(s):  
Density Functional Calculations ◽  
Density Functional ◽  
Basis Sets ◽  
General Interest ◽  
Molecular Anion ◽  
Substituent Group ◽  
Endor Spectroscopy ◽  
Disubstituted Benzene ◽  
Disubstituted Derivative ◽  
Reduction Behaviour

The attempted crystal growth of 1,4-bis(tricyanovinyl)benzene dianion salts, although without success so far, has provided information of general interest. The crystal structures of the related mono and 1,4-bis(tricyanovinyl)benzene derivatives differ considerably in their substituent group twisting angles: The two tricyanovinylbenzenes in split-positions exhibit dihedral angles of only 6° or 11°, whereas the two C2(CN)3 groups of the disubstituted benzene are conrotationally twisted by 48° out of the benzene plane. Density functional calculations with 6 - 311++G** basis sets, however, predict identical values of 32° for both compounds and, therefore, their crystal arrangements are discussed in detail for packingenforced additional interactions. Cyclovoltammetric and ESR/ENDOR-measurements provide information on the redox behaviour, a prerequisite for attempts to crystallize molecular anion salts: The 1,4-disubstituted derivative with a cyclovoltammetrically determined halfwave reduction potential of +.14 V in aprotic THF solution proves to be one of the strongest polycyano-substituted π-acceptors and its radical anion can be selectively generated by T1 metal reduction as confirmed by its ESR/ENDOR spectra.

Response Function Basis Sets:  Application to Density Functional Calculations

1996 ◽  
Vol 100 (15) ◽  
pp. 6231-6235 ◽  
Author(s):  
Gerald Lippert ◽  
Jürg Hutter ◽  
Pietro Ballone ◽  
Michele Parrinello
Keyword(s):  
Response Function ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Basis Sets

Rate Coefficients for Intramolecular Homolytic Substitution of Oxyacyl Radicals at Sulfur

2013 ◽  
Vol 66 (3) ◽  
pp. 323 ◽  
Author(s):  
Heather M. Aitken ◽  
Sonia M. Horvat ◽  
Michelle L. Coote ◽  
Ching Yeh Lin ◽  
Carl H. Schiesser
Keyword(s):  
Free Energy ◽  
Ab Initio ◽  
Gas Phase ◽  
Sulfur Atom ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Rate Coefficients ◽  
Energy Barriers ◽  
Tert Butyl ◽  
Homolytic Substitution

It is predicted on the basis of ab initio and density functional calculations that intramolecular homolytic substitution of oxyacyl radicals at the sulfur atom in ω-alkylthio-substituted radicals do not involve hypervalent intermediates. With tert-butyl as the leaving radical, free energy barriers ΔG‡ (G3(MP2)-RAD) for these reactions range from 45.8 kJ mol–1 for the formation of the five-membered cyclic thiocarbonate (8) to 56.7 kJ mol–1 for the formation of the six-membered thiocarbonate (9). Rate coefficients in the order of 104–106 s–1 and 101–104 s–1 for the formation of 8 and 9, respectively, at 353.15 K in the gas phase are predicted at the G3(MP2)-RAD level of theory.

What Silicon Nanocluster is Most Likely Formed in Etching Experiments? Theoretical DFT Study

2008 ◽  
Vol 8 (7) ◽  
pp. 3478-3482
Author(s):  
Nurbosyn U. Zhanpeisov ◽  
Hiroshi Fukumura
Keyword(s):  
Absorption Spectra ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Electrochemical Etching ◽  
Time Dependent ◽  
Cluster Models ◽  
Dft Study ◽  
Basis Sets ◽  
Self Healing ◽  
Tddft Calculations

Density functional calculations at the B3LYP/6-31G* level were performed for Si nanoclusters of ca.1 nm in size. The structural, energetic, electronic as well as the estimated absorption spectra by the time-dependent DFT (TDDFT) calculations using varied functionals and basis sets for the representative cluster models are all in favor of the formation of most probable Si35H36 nanocluster in recent electrochemical etching experiments. The nanostructure has a complete H-termination at the borderline regions and lacks from the presence of any defects like surface Si—Si dimer units formed via self-healing of dangling Si—Si bonds or from any relatively short H…H contacts.

scholarly journals Μελέτη της δομής και της φυσικοχημικής συμπεριφοράς μέταλλο-υποκατεστημένων αρενίων με μέταλλα της 11ης ομάδας

2017 ◽  
Author(s):  
Δημήτριος Γκαρμπούνης
Keyword(s):  
Density Functional Theory ◽  
Chemical Shift ◽  
Density Functional ◽  
Natural Bond Orbital ◽  
Electron Localization ◽  
Functional Theory ◽  
Nucleus Independent Chemical Shift ◽  
Reduced Density Gradient ◽  
Reduced Density ◽  
Homo Lumo

Στην παρούσα διατριβή μελετήθηκε μια σειρά υποκατεστημένων βενζολικών δακτυλίων με άτομα μετάλλων νομισματοκοπείου του γενικού τύπου C6H6-nMn (M = Cu, Ag, Au, n = 1 – 6), με τη βοήθεια της μεθόδου συναρτησιακού πυκνότητας (Density Functional Theory), που χαρακτηρίζεται με το ακρώνυμο DFT. Συγκεκριμένα μελετήθηκαν διεξοδικά τόσο οι δομικές όσο και οι ενεργειακές, μαγνητοτροπικές και φασματοσκοπικές ιδιότητες των παραπάνω ενώσεων και συγκρίθηκαν με τις αντίστοιχες ιδιότητες του μη υποκαταστημένου αρωματικού βενζολικού δακτυλίου. Σε αντίθεση με τον βενζολικό δακτύλιο, τα μεταλλουποκαταστημένα βενζόλια του τύπου C6H6-nMn (M = Cu, Ag, Au, n = 1 – 6) παρουσιάζουν αρωματικό χαρακτήρα ακόμα και στην τριπλή διεγερμένη κατάστασή τους. Από τη μελέτη αυτή προέκυψαν πολύ καλές γραμμικές συσχετίσεις του τανυστή zz στο σημείο 1, NICSzz(1), του δείκτη αρωματικότητας NICS (Nucleus Independent Chemical Shift), 1) με το συνολικό αρνητικό φυσικό φορτίο που φέρει ο καρβοκυκλικός δακτύλιος και 2) με το μήκος κύματος (λ) της μετάπτωσης HOMO → LUMO στα φάσματα απορρόφησης των ενώσεων C6H6-nMn. Τα φάσματα εκπομπής των ενώσεων C6H6-nMn χαρακτηρίζονται από τις υψηλές τιμές της διαφοράς ενέργειας ΔE(S0-T1) ειδικά στις περιπτώσεις των δι-υποκατεστημένων μέτα- και πάρα- ισομερών. Η μέγιστη τιμή ΔE(S0-T1) που υπολογίστηκε για την ένωση m-C6H4Au2 είναι ίση με 67 kcal/mol. Μελετήθηκαν επίσης τα δεσμικά χαρακτηριστικά των μετάλλων Cu, Ag, Au με τους βενζολικούς δακτυλίους για κάθε περίπτωση, με τη βοήθεια διαφόρων υπολογιστικών κβαντοχημικών μεθόδων, όπως είναι η πλυθησμιακή ανάλυση φυσικών τροχιακών δεσμού (Natural Bond Orbital, NBO), η πλυθησμιακή ανάλυση με τη μέθοδο των Ατόμων-Στα-Μόρια (Atoms-In-Molecules, AIM), τη συνάρτηση ηλεκρονιακού εντοπισμού (Electron Localization Function, ELF), την κλίση ανηγμένης πυκνότητας (Reduced Density Gradient, RDG) και οι συναρτήσεις Sign(λ2(r))ρ(r) για ακόμα μεγαλύτερη ακρίβεια. Η θεωρητική μελέτη των ενώσεων C6H6-nMn (M = Cu, Ag, Au, n = 1 – 6) έδειξε ότι αυτές είναι θερμοδυναμικά σταθερές και κατά συνέπεια θα ήταν δυνατή η σύνθεση και απομόνωσή τους από πειραματικούς χημικούς.Επίσης, μελετήθηκε, με μεθόδους της DFT, η ικανότητα αντιπρωσοπευτικών ενώσεων, όπως του C6H5Cu και 1,3,5-Cu3C6H3 για τη δέσμευση και αποθήκευση μοριακού υδρογόνου και βρέθηκε να τηρούν τις απαιτήσεις του US DOE για χαμηλού κόστους υλικών αποθήκευσης υδρογόνου. Μια εμπεριστατωμένη ανάλυση των δεσμικών Cu∙∙∙(η2-H2) αλληλεπιδράσεων με τη βοήθεια υπολογιστικών μεθόδων ηλεκτρονικής δομής (NBO, AIM, ELF, RDG και συναρτήσεων Sign(λ2(r))ρ(r)) έδειξε ότι οι αλληλεπιδράσεις αυτές εμφανίζουν έναν μικτό ομοιοπολικό - ιοντικό χαρακτήρα που συνοδεύεται από ασθενείς διαμοριακές αλληλεπιδράσεις διασποράς.

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