Pressure Effects upon the Rates of Aquation of Halopentaamminechromium(III) Ions: Evidence for an Associative Mechanism

1973 ◽  
Vol 51 (6) ◽  
pp. 821-827 ◽  
Author(s):  
G. Guastalla ◽  
T. W. Swaddle
Keyword(s):  
Transition State ◽  
Molar Volume ◽  
Pressure Dependence ◽  
Ground State ◽  
Pressure Effects ◽  
Water Molecules ◽  
Associative Mechanism

For the replacement of X− by H2O in Cr(NH3)5X2+, ΔVo* (the value of the volume of activation ΔV* at zero pressure) at 25.0° in 0.1 m NH4ClO4 is −10.8, −10.2, and − 9.4 cm3 mol−1 respectively for X− = Cl−, Br−, and I−, while ΔV, the molar volume of reaction, is −8.4, −7.2 and −6.0 cm3 mol−1. The pressure-dependence of ΔV* can be expressed in terms of the number x of water-molecules which are electrostricted as the systems go from ground-state to transition-state; for X− = Cl−, Br−, and I−, x = 1.9, 2.0, and 1.7. These data, combined with ΔV* = −5.8 cm3 mol−1 for the aquo-exchange of Cr(NH3)5OH23+, indicate an associative mechanism for these reactions, as does the contrast with ΔV0* data for the formally analogous, but dissociatively-activated, reactions of Co(NH3)5X(3−n)+.

Investigation of the Pressure Effects on Inclusion Equilibria of Substituted Phenols with β- and γ-Cyclodextrins

2003 ◽  
Vol 217 (6) ◽  
pp. 677-688 ◽  
Author(s):  
Yoshimi Sueishi ◽  
Shotaro Itami
Keyword(s):  
Pressure Dependence ◽  
Inclusion Complexation ◽  
Pressure Effects ◽  
Water Molecules ◽  
Substituted Phenols ◽  
Reaction Volume ◽  
The Difference ◽  
Reaction Volumes

AbstractThe effects of pressure were examined for the inclusion complexation of β- and γ-cyclodextrins (CDs) with 4-substituted phenols. The reaction volume for the CD inclusion complexation with 4-substituted phenols, which is the change in volume accompanied by CD inclusion, was estimated from the pressure dependence of the inclusion equilibria. The reaction volumes estimated for the phenols/β-CD system were positive values in the range of 2.5 and 14.0cm3mol−1, while those for the phenols/γ-CD system were negative in the range of −11.8 and −0.8cm3mol−1. The difference in the reaction volumes for the inclusion complexation of β- and γ-CDs is explained in terms of the difference in the number of water molecules repelled from the CD cavity. Based on the results, the inclusion behavior of CD complexation is discussed.

Effect of Medium on Reactivity for Alkaline Hydrolysis of p-Nitrophenyl Acetate and S-p-Nitrophenyl Thioacetate in DMSO-H2O Mixtures of Varying Compositions: Ground State and Transition State Contributions

2021 ◽  
Author(s):  
Ik-Hwan Um ◽  
Seungjae Kim
Keyword(s):  
Transition State ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Medium ◽  
Stepwise Mechanism ◽  
Rate Determining Step ◽  
Leaving Group ◽  
Hydrolysis Of

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH‒ have been measured spectrophotometrically in DMSO-H2O mixtures of varying compositions at 25.0 ± 0.1 oC. The kN value increases from 11.6 to 32,800 M‒1s‒1 for the reactions of 1 and from 5.90 to 190,000 M‒1s‒1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state (TS), i.e., the reactions of 1 and 2 with OH‒ proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step (RDS). Addition of DMSO to H2O would destabilize OH‒ through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH‒ in the ground state (GS) is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the GS and TS contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO-H2O mixtures for OH‒ ion.

Communication: Photodissociation of CH3CHO at 308 nm: Observation of H-roaming, CH3-roaming, and transition state pathways together along the ground state surface

2015 ◽  
Vol 142 (4) ◽  
pp. 041101 ◽  
Author(s):  
Hou-Kuan Li ◽  
Po-Yu Tsai ◽  
Kai-Chan Hung ◽  
Toshio Kasai ◽  
King-Chuen Lin
Keyword(s):  
Transition State ◽  
Ground State

scholarly journals SN2 regioselectivity in the esterification of 5- and 7-membered azacycloalkane quaternary salts: a DFT study to reveal the transition state ring conformation prevailing over the ground state ring strain

2014 ◽  
Vol 12 (34) ◽  
pp. 6717-6724 ◽  
Author(s):  
Akihiro Kimura ◽  
Susumu Kawauchi ◽  
Takuya Yamamoto ◽  
Yasuyuki Tezuka
Keyword(s):  
Transition State ◽  
Ground State ◽  
Dft Study ◽  
Ring Conformation ◽  
Ring Strain ◽  
Quaternary Salts

SN2 regioselectivity in 5- and 7-membered azacycloalkanes quaternary salts is directed by the transition state ring conformation.

scholarly journals Pressure Effects on the Magnetic Phase Diagram of the CeNMSb2 (NM: Au and Ag): A DFT Study

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2237
Author(s):  
Mowafaq Mohammad Alsardia ◽  
Jaekyung Jang ◽  
Joo Yull Rhee
Keyword(s):  
Ground State ◽  
Noble Metals ◽  
Easy Axis ◽  
Magnetic Phase ◽  
Magnetic Phase Diagram ◽  
Pressure Effects ◽  
Spin Orbit ◽  
Magnetic Ground State ◽  
Magnetic Easy Axis ◽  
Spin Orbit Interactions

We explore the influence of pressure on the magnetic ground state of the heavy-fermion antiferromagnet (ferromagnet) CeAuSb 2 (CeAgSb 2 ) using first-principles calculations. The total-energy differences obtained by including the spin-orbit interactions and the on-site Coulomb potential for the Ce-derived 4f-orbitals are necessary to realize the accurate magnetic ground state of CeNMSb 2 (NM: Au and Ag). According to our results, the appearance of a new magnetic phase of CeAuSb 2 (CeAgSb 2 ) at the pressure of 2.1 GPa (3.5 GPa) is due to the rotation of the magnetic easy axis from the <001> to the <100> direction. Additionally, our data confirm that CeAgSb 2 is antiferromagnetic (AFM) above a critical pressure P c , and such a tendency is expected for CeAuSb 2 and remains to be seen. Through the spin-orbit-coupling Hamiltonian and detailed information on the occupation of individual 4f-orbitals of the Ce atom obtained by the electronic-structure calculations, we can deduce the rotation of the magnetic easy axis upon the application of pressure. According to the present and previous studies, the differences among the magnetic properties of CeNMSb 2 (NM: Cu, Ag and Au) compounds are not due to the different noble metals, but due to the subtle differences in the relative position of Ce atoms and, in turn, different occupations of Ce 4f-orbitals.

The effect of pressure on excimer formation

1965 ◽  
Vol 18 (7) ◽  
pp. 977 ◽  
Author(s):  
H Seidel ◽  
BK Selinger
Keyword(s):  
Excited State ◽  
Hydrostatic Pressure ◽  
Molar Volume ◽  
Aromatic Hydrocarbons ◽  
Ground State ◽  
Dominant Factor ◽  
Effect Of Pressure ◽  
Excimer Formation ◽  
Ground State Molecule ◽  
True Equilibrium

The formation of excited dimers by aromatic hydrocarbons in solution was found to be influenced by hydrostatic pressure. The increase in the viscosity of the solvent with pressure is the dominant factor for the more stable excited dimers and this causes a decrease in the amount of dimer with increasing pressure. Where there is a true equilibrium between excited dimer and monomer an increase in pressure causes an increase in dimer concentration. The change in molar volume for the formation of an excited dimer of 1,6-dimethylnaphthalene from a ground state molecule and one in the excited state was found to be -20 cm3 mole-1, representing a 10% reduction.

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