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

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.

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.

Intramolekulare Austauschprozesse in Cyclopentadienyl-Systemen. Strukturabhängigkeit der Energiebarrieren / Intramolecular Exchange Processes in Cyclopentadien Systems. Structural Dependence of Activation Barrieres

1978 ◽  
Vol 33 (1) ◽  
pp. 94-99 ◽  
Author(s):  
Klaus Albert ◽  
Jürgen Hambrecht
Keyword(s):  
Energy Level ◽  
Transition State ◽  
Ground State ◽  
State Energy ◽  
Temperature Dependent ◽  
Structural Dependence ◽  
H Nmr ◽  
Intramolecular Exchange ◽  
Exchange Processes ◽  
Phenyl Rings

Abstract ⊿Gc ≠ values derived from temperature dependent 1H NMR of phenyl substituted cyclopentadienes show a dramatic increase by immobilizing two phenyl-rings. This phenomenon is explained by an increase in the transition state energy level whereas the ground state is hardly affected.

High accuracy studies on the ground state and transition state of SiC2

1998 ◽  
Vol 454 (1) ◽  
pp. 31-40 ◽  
Author(s):  
Yong Zhang ◽  
Cun-Yuan Zhao ◽  
Wei-Hai Fang ◽  
Zu-Hong Lu
Keyword(s):  
Transition State ◽  
Ground State ◽  
High Accuracy

THEORETICAL STUDY ON INTERNAL ROTATION OF NITROSOUREAS AND TOXICOLOGICAL ANALYSIS

2007 ◽  
Vol 06 (02) ◽  
pp. 245-253 ◽  
Author(s):  
YA SONG CUI ◽  
LI JIAO ZHAO ◽  
YONG DONG LIU ◽  
RU GANG ZHONG
Keyword(s):  
Transition State ◽  
Internal Rotation ◽  
Ground State ◽  
Energy Barrier ◽  
Theoretical Study ◽  
Rotational Energy ◽  
Carcinogenic Potency ◽  
Toxicological Analysis ◽  
Ground State Structures ◽  
The Relationship

A theoretical study has been carried out for internal rotation of nitrosoureas at the B3LYP/6-311G* level of theory. For each nitrosourea compound, two ground state structures have been found and the E isomer is predicted to be more stable than the Z isomer. Two transition state conformations for the isomerization have also been obtained and the calculated results show that the isomerization through TS1 is easier than that through TS2. The relationship between energy barrier and toxicity has also been investigated. It is concluded that the carcinogenic potency increases along with the decrease of rotational energy barrier.

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