TY - JOUR
T1 - Theoretical calculations on the gas-phase thermal decomposition kinetics of selected thiomethyl chloroalkanes
T2 - A new insight of the mechanism
AU - Luiggi, Marniev
AU - Mora, José R.
AU - Loroño, Marcos
AU - Marquez, Edgar
AU - Lezama, Jesus
AU - Cordova, Tania
AU - Chuchani, Gabriel
N1 - Copyright:
Copyright 2013 Elsevier B.V., All rights reserved.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - Theoretical calculations of the gas-phase thermal decomposition kinetics of 2-thiomethyl-1-chloroethane and 4-thiomethyl-1-chlorobutane have been carried out by using Density Functional Theory (DFT), composite CBS-Q3, and Møller-Plesset second-order (MP2) methods in order to elucidate a reasonable reaction mechanism of these compounds. The enhanced reactivities of these two substrates, when compared with their parent compounds, attributed to neighboring group participation (NGP) or anquimeric assistance in the literature, were investigated. For 2-thiomethyl-1-chloroethane two dehydrochlorinaton pathways, with and without NGP were studied. The results of quantum chemical estimations of 2-thiomethyl-1-chloroethane in the gas phase show good agreement with experimental values at B3LYP/6-31++G(2d,p) level, and suggest the 1,2-elimination through non-synchronous four-membered cyclic transition state is the preferred mechanism. For 4-thiomethyl-1-chlorobutane, the significant increase in rate compared to 2-thiomethyl-1-chloroethane, together with the formation of a cyclic product tetrahydrothiophene suggest the anchimeric assistance by the CH3S group in the transition state. Best calculated parameters were obtained with CAM-B3LYP/6-31G++(2d,p). Results support the NGP of the thiomethyl group, through cyclic ion-pair type of intermediate. The bond polarization of the C-Cl, in the direction of Cδ+⋯Clδ-, appears to be the rate determining step of these decompositions.
AB - Theoretical calculations of the gas-phase thermal decomposition kinetics of 2-thiomethyl-1-chloroethane and 4-thiomethyl-1-chlorobutane have been carried out by using Density Functional Theory (DFT), composite CBS-Q3, and Møller-Plesset second-order (MP2) methods in order to elucidate a reasonable reaction mechanism of these compounds. The enhanced reactivities of these two substrates, when compared with their parent compounds, attributed to neighboring group participation (NGP) or anquimeric assistance in the literature, were investigated. For 2-thiomethyl-1-chloroethane two dehydrochlorinaton pathways, with and without NGP were studied. The results of quantum chemical estimations of 2-thiomethyl-1-chloroethane in the gas phase show good agreement with experimental values at B3LYP/6-31++G(2d,p) level, and suggest the 1,2-elimination through non-synchronous four-membered cyclic transition state is the preferred mechanism. For 4-thiomethyl-1-chlorobutane, the significant increase in rate compared to 2-thiomethyl-1-chloroethane, together with the formation of a cyclic product tetrahydrothiophene suggest the anchimeric assistance by the CH3S group in the transition state. Best calculated parameters were obtained with CAM-B3LYP/6-31G++(2d,p). Results support the NGP of the thiomethyl group, through cyclic ion-pair type of intermediate. The bond polarization of the C-Cl, in the direction of Cδ+⋯Clδ-, appears to be the rate determining step of these decompositions.
KW - 2-Thiomethyl-1-chloroethane
KW - 4-Thiomethyl-1-chlorobutane
KW - Kinetics
KW - Theoretical calculations
KW - Thermal decomposition
UR - http://www.scopus.com/inward/record.url?scp=84889017276&partnerID=8YFLogxK
U2 - 10.1016/j.comptc.2013.11.011
DO - 10.1016/j.comptc.2013.11.011
M3 - Artículo
AN - SCOPUS:84889017276
SN - 2210-271X
VL - 1027
SP - 165
EP - 172
JO - Computational and Theoretical Chemistry
JF - Computational and Theoretical Chemistry
ER -