scholarly journals Infrared intensities of imaginary frequencies: Gas-Phase SN2 Transition States

2020 ◽  
Author(s):  
Leonardo José Duarte ◽  
Roy Edward Bruns
Keyword(s):  
Charge Transfer ◽  
Gas Phase ◽  
Normal Mode ◽  
Transition States ◽  
Normal Modes ◽  
Leaving Group ◽  
Infrared Intensity ◽  
Infrared Intensities ◽  
Almost All ◽  
Electron Transfers

The gas phase SN2 reaction transition state structures for nine [XCZ_3 Y]^- systems, where X,Y=H,F,Cl and Z = H,F were optimized and their normal modes of vibrations were determined at the QCISD/aug-cc-pVTZ level of theory. Using Quantum Theory of Atoms in Molecules (QTAIM), the atomic charges and atomic dipoles were obtained and used to calculate the Charge – Charge Transfer – Dipolar Polarization (CCTDP) contributions to the imaginary normal mode intensity of transition states. The results show that the imaginary bands are strong, ranging from 1217 to 16086 〖km∙mol〗^(-1), much higher than occurs for most bands found in molecules. For all systems, the CT contribution is responsible for 80% of the total intensity on average. The Charge contributions are slightly higher for transitions states with Z = F. Dipolar polarization contributions are always small. The contributions from the Z atoms are negligible, thus only atoms aligned with the reaction axis X-C-Y contribute to total intensity. All charge transfers were evaluated taking the carbon atom as reference, implying that almost all infrared intensity is determined by electron transfers from the nucleophile and carbon and from carbon to the leaving group. The mechanism of charge transfer revealed by the CCTDP model is consistent with the reaction mechanism itself, which points towards the connection between the imaginary normal mode and the reaction coordinate.

Reactivity patterns of N-methylbenzhydroxamates. I. Studies of methyl transfer between N-methylbenzhydroxamates and arenesulfonates

1991 ◽  
Vol 69 (5) ◽  
pp. 798-810 ◽  
Author(s):  
Kenneth R. Fountain ◽  
Daniel P. Fountain ◽  
Bernice Michaels ◽  
D. Brenton Myers ◽  
Jon K. Salmon ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Charge Transfer ◽  
Key Words ◽  
Gas Phase ◽  
Ionization Potentials ◽  
Carbonyl Groups ◽  
Methyl Transfer ◽  
Effect Model ◽  
Leaving Group ◽  
Leaving Groups

The rates of methyl transfer between benzohydroxamates and sulfonates show large βnuc values (ca. 0.8) indicating much charge transfer to the C atom, similar to the results of N,N-dialkylaminofluorene anions. A small α effect shows that even in methyl substrates, with certain leaving groups, the effect is displayed. Investigation of the β1g shows that from the leaving group side of the reaction it is a normal SN2 reaction. Correlation of the reactivity with computed gas phase ionization potentials shows that desolvation of anions is probably not important. These results suggest an α-effect model that explains the larger size of the effect at carbonyl groups in terms of greater solvation of the charge transferred to the O atom. Key words: α effect, Brønsted plot, ionization potentials, cyclic voltammetry, β1g, βnuc, AMl, [Formula: see text]

scholarly journals Preparation and the Microwave and Infrared Spectra of Vinyl Ketene

1979 ◽  
Vol 34 (11) ◽  
pp. 1269-1274 ◽  
Author(s):  
Erik Bjarnov
Keyword(s):  
Dipole Moment ◽  
Gas Phase ◽  
Infrared Spectra ◽  
Room Temperature ◽  
Normal Modes ◽  
Spectroscopic Constants ◽  
Electrical Dipole ◽  
Electrical Dipole Moment ◽  
Vacuum Pyrolysis ◽  
Modes Of Vibration

Vinyl ketene (1,3-butadiene-1-one) has been synthesized by vacuum pyrolysis of 3-butenoic 2-butenoic anhydride. The microwave and infrared spectra of vinyl ketene in the gas phase at room temperature have been studied. The trans-rotamer has been identified, and the spectroscopic constants were found to be Ã= 39571(48) MHz, B̃ = 2392.9252(28) MHz, C̃ = 2256.0089(28) MHz, ⊿j = 0.414(31) kHz, and ⊿JK = - 34.694(92) kHz. The electrical dipole moment was found to be 0.987(23) D with μa = 0.865(14) D and μb = 0.475(41) D. A tentative assignment has been made for 17 of the 21 normal modes of vibration

Acoustic Green's Function Approximations

1998 ◽  
Vol 06 (04) ◽  
pp. 435-452 ◽  
Author(s):  
Robert P. Gilbert ◽  
Zhongyan Lin ◽  
Klaus Hackl
Keyword(s):  
Inverse Problem ◽  
Normal Mode ◽  
Eigenvalue Problems ◽  
Normal Modes ◽  
Modal Parameters ◽  
Mindlin Plate ◽  
Ocean Bottom ◽  
Hankel Transformation ◽  
Poroelastic Materials ◽  
Function Approximations

Normal-mode expansions for Green's functions are derived for ocean–bottom systems. The bottom is modeled by Kirchhoff and Reissner–Mindlin plate theories for elastic and poroelastic materials. The resulting eigenvalue problems for the modal parameters are investigated. Normal modes are calculated by Hankel transformation of the underlying equations. Finally, the relation to the inverse problem is outlined.

Experimental Study for Extraction of Normal Modes

1995 ◽  
Author(s):  
S. Y. Chen ◽  
M. S. Ju ◽  
Y. G. Tsuei
Keyword(s):  
Frequency Response ◽  
Normal Mode ◽  
Normal Modes ◽  
Measurement Data ◽  
Mode Shapes ◽  
Complex Frequency ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Incomplete System ◽  
Coupled Structures

Abstract A frequency-domain technique to extract the normal mode from the measurement data for highly coupled structures is developed. The relation between the complex frequency response functions and the normal frequency response functions is derived. An algorithm is developed to calculate the normal modes from the complex frequency response functions. In this algorithm, only the magnitude and phase data at the undamped natural frequencies are utilized to extract the normal mode shapes. In addition, the developed technique is independent of the damping types. It is only dependent on the model of analysis. Two experimental examples are employed to illustrate the applicability of the technique. The effects due to different measurement locations are addressed. The results indicate that this technique can successfully extract the normal modes from the noisy frequency response functions of a highly coupled incomplete system.

Mechanisms of aromatic nucleophilic substitution by the ambident thiocyanate ion

1973 ◽  
Vol 26 (2) ◽  
pp. 273 ◽  
Author(s):  
DE Giles ◽  
AJ Parker
Keyword(s):  
Nucleophilic Substitution ◽  
Transition States ◽  
Reactivity Ratio ◽  
Substitution Reactions ◽  
Aromatic Nucleophilic Substitution ◽  
Thiocyanate Ion ◽  
Sn2 Reactions ◽  
Leaving Group ◽  
Electrophilic Reactivity ◽  
Saturated Carbon Atom

Sulphur/nitrogen reactivity ratios in a series of aromatic nucleophilic substitution reactions of ambident thiocyanate ion have been determined. There are profound differences from the pattern found in SN2 reactions at a saturated carbon atom. Abnormal transition states, involving interactions between entering and leaving group, are likely in the bond-breaking step of the intermediate complex in reactions of thiocyanate ion with 1-fluoro-2,4-dinitrobenzene and with 2,4- dinitrophenyl 4-toluenesulphonate. The nitro-substituted aryl thiocyanates are shown to be tri-functional electrophiles, with reactive centres at aromatic carbon, at cyanide carbon, and at sulphur. Aryl 4-toluenesulphonates are bifunctional electrophiles with reactive centres at aryl carbon and sulphonyl sulphur. The site of attack by nucleophiles depends on the nature of the nucleophile. The sulphur/nitrogen reactivity ratio of ambident SCN-, and the electrophilic reactivity of tri- and bi-functional substrates, are in most instances consistent with the Hard and Soft Acids and Bases principle. Exceptions to the principle in some instances reveal differences between the SNAr and SN2 mechanisms, and in others indicate abnormal transition states.

scholarly journals Computational notes on the electronic properties of carboxylic acid

2020 ◽  
Vol 9 (2) ◽  
pp. 1079-1082
Keyword(s):  
Acetic Acid ◽  
Carboxylic Acid ◽  
Electronic Properties ◽  
Carboxylic Acids ◽  
Normal Mode ◽  
Normal Modes ◽  
Carboxyl Groups ◽  
Vibrational Characteristics ◽  
Vibrational Features ◽  
Acetic Acids

The present work describing the electronic properties and vibrational characteristics of carboxylic acids. Acetic acid is chosen as model molecules then optimized at B3LYP/6-31g(d,p) level of theory. The vibrational frequencies were calculated at the same level of theory. Band assignments which were calculated as 18 normal modes were assigned as one compare the normal mode coordinates with original one. Band assignments were described indicating the directions of normal modes in terms the vibrating atoms of the acetic acids. It could be concluded that DFT could be a useful tool for elucidation both the structural and vibrational features of carboxylic acids and then further utilized for assignment of the structures contains carboxyl groups which are known as most reactive structures in chemistry, biology and environment.

scholarly journals The Gas-phase Chemical Evolution of Dark Clouds

1992 ◽  
Vol 45 (4) ◽  
pp. 451
Author(s):  
RPA Bettens
Keyword(s):  
Gas Phase ◽  
Chemical Species ◽  
Dynamical Evolution ◽  
Constant Density ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Chemical Models ◽  
Almost All ◽  
Present Understanding ◽  
Phase Chemical

A rich chemistry exists within dark clouds. In the most chemically studied dark cloud, Taurus molecular cloud one (TMC-l), more than 40 molecules have been detected. In this paper I look at the current isochoric, i.e. constant density, isothermal time-dependent gas-phase chemical models of dark clouds such as TMC-l and very briefly outline the present understanding of the chemistry of these objects. The above chemical models agree very well with the observed abundances of almost all chemical species at times earlier than steady state, i.e. earlier than thirty million years. However, the models are fraught with uncertainty and are not physically realistic representations of the full dynamical evolution of dark clouds from a more diffuse state. Nevertheless the agreement with observation is striking.

scholarly journals Normal modes in thermal AdS via the Selberg zeta function

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Victoria Martin ◽  
Andrew Svesko
Keyword(s):  
Zeta Function ◽  
Heat Kernel ◽  
Normal Mode ◽  
Kernel Method ◽  
Normal Modes ◽  
Quasinormal Mode ◽  
Partition Functions ◽  
Selberg Zeta Function ◽  
Exact Agreement ◽  
Spin Fields

The heat kernel and quasinormal mode methods of computing 1-loop partition functions of spin ss fields on hyperbolic quotient spacetimes \mathbb{H}^{3}/\mathbb{Z}ℍ3/ℤ are related via the Selberg zeta function. We extend that analysis to thermal \text{AdS}_{2n+1}AdS2n+1 backgrounds, with quotient structure \mathbb{H}^{2n+1}/\mathbb{Z}ℍ2n+1/ℤ. Specifically, we demonstrate the zeros of the Selberg function encode the normal mode frequencies of spin fields upon removal of non-square-integrable modes. With this information we construct the 1-loop partition functions for symmetric transverse traceless tensors in terms of the Selberg zeta function and find exact agreement with the heat kernel method.

scholarly journals Tuning of Hyperpolarizability, One- and Two-Photon Absorption of D-A and D-A-A Type Intramolecular Charge Transfer Based Sensors

2019 ◽  
Author(s):  
Pralok K. Samanta ◽  
Md Mehboob Alam ◽  
Ramprasad Misra ◽  
Swapan K. Pati
Keyword(s):  
Charge Transfer ◽  
Gas Phase ◽  
Density Functional ◽  
Intramolecular Charge Transfer ◽  
Photon Absorption ◽  
First Hyperpolarizability ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Nlo Response ◽  
Donor Acceptor

Solvents play an important role in shaping the intramolecular charge transfer (ICT) properties of π-conjugated molecules, which in turn can affect their one-photon absorption (OPA) and two-photon absorption (TPA) as well as the static (hyper)polarizabilities. Here, we study the effect of solvent and donor-acceptor arrangement on linear and nonlinear optical (NLO) response properties of two novel ICT-based fluorescent sensors, one consisting of hemicyanine and dimethylaniline as electron withdrawing and donating groups (molecule 1), respectively and its boron-dipyrromethene (BODIPY, molecule 2)-fused counterpart (molecule 3). Density functional theoretical (DFT) calculations using long-range corrected CAM-B3LYP and M06-2X functionals, suitable for studying properties of ICT molecules, are employed to calculate the desired properties. The dipole moment (µ) as well as the total first hyperpolarizability (β<sub>total</sub>) of the studied molecules in the gas phase is dominantly dictated by the component in the direction of charge transfer. The ratios of vector component of first hyperpolarizability (β<sub>vec</sub>) to β<sub>total</sub> also reveal unidirectional charge transfer process. The properties of the medium significantly affect the OPA, hyperpolarizability and TPA properties of the studied molecules. Time dependent DFT (TDDFT) calculations suggest interchanging between two lowest excited states of molecule 3 from the gas phase to salvation. The direction of charge polarization and dominant transitions among molecular orbitals involved in the OPA and TPA processes are studied. The results presented are expected to be useful in tuning the NLO response of many ICT-based chromophores, especially those with BODIPY acceptors.<br>

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