Hasil untuk "Physical and theoretical chemistry"

A.A. Kachina

Makesh Mohan, M.N. Satyanarayan, Darshak R. Trivedi

AbstractHydrazides are known to exhibit keto‐enol tautomerism upon photoexcitation. Theoretical aspects uncovering excited state intramolecular proton transfer (ESIPT) of N‐acylsubstituted hydrazides with bithiophene core have been investigated. Geometrical aspects of the system are expected to undergo double proton translocation at its excited state. However, potential energy surface study for all the molecules reveals an impossible concurrent double proton translocation and to a greater extent dubious step‐wise double proton translocation in the system. Potential energy scans reveal molecules possessing a lower forward barrier at its excited state in comparison with their ground state suggestive of possible excited state single proton transfer. Geometrical attributes and spectral analysis suggest the strengthening of intramolecular hydrogen bond (N―H▪▪▪O) at its excited state, favoring single proton translocation. Theoretical estimation of electronic energy transition for all the conformers yields good correlation with the experimental figures with an energy overestimation <0.17 eV.

Benoît Braïda, Shina Caroline Lynn Kamerlin

Zerong Daniel Wang, Motoko Yoshida, Ben George

Javad Beheshtian, Ali Ahmadi Peyghan, Zargham Bagheri

Philip M. Kiefer, James T. Hynes

AbstractThis paper reviews some nontraditional theoretical views developed in this group on acid–base proton transfer (PT) reactions in hydrogen (H‐) bonded systems, focusing on the tunneling regime. Key ingredients in this picture are a completely quantum character for the proton motion (even when tunneling does not occur), the identification of a solvent coordinate as the reaction coordinate, and attention to the H‐bond vibrational ‘promoting’ mode in the acid–base complex. Attention is also given to the electronic structure rearrangements associated with PT in the electronically adiabatic regime. A general overview is presented for the tunneling rate constants including the activation free energy and the associated primary kinetic isotope effects (KIEs) for proton tunneling reactions. Copyright © 2010 John Wiley & Sons, Ltd.

Sébastien Canneaux, Adrien Wallet, Marc Ribaucour et al.

Julianto Pranata, Dennis A. Dougherty

AbstractCyclobutanediyl (2) has been studied in both its singlet and triplet states by ab initio electronic structure theory. The triplet, which is the ground state of the molecule, exists in both C2h and C2v forms which interconvert via a Cs transition state. For the singlet, only a C2h form is found. It passes, via a Cs transition state, onto the C2v surface on which bicyclobutane (3) is the only minimum. The ring‐flipping (inversion) process in 3 includes the singlet biradical as an intermediate, and involves a novel, non‐least motion path similar to one previously proposed by Gassman. Semiclassical periodic orbit theory indicates that the various minima on both the singlet and triplet surfaces can interconvert via quantum mechanical tunneling.

Jochen Winkelmann

J. A. Ladd

Steven M. Bachrach

Ping Wu, Xiaoping Chen, Jiaxing Li et al.

Alexander Starik, Alexander Sharipov

Otto Dopfer

Andreas Köhn, Florian Weigend, Reinhart Ahlrichs

William G. Hoover, William T. Ashurst

Yahia Moussaoui, Ourida Ouamerali, George R. De Maré

Gregory A. Voth