Premium
Theoretical study of neighboring group participation of methyl ω ‐chloroesters elimination kinetics in the gas phase
Author(s) -
Romero Mery Lorena,
Cordova Tania,
Chuchani Gabriel
Publication year - 2009
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1474
Subject(s) - chemistry , transition state , methyl group , natural bond orbital , computational chemistry , elimination reaction , leaving group , concerted reaction , kinetics , transition state theory , reaction mechanism , stereochemistry , thermodynamics , density functional theory , reaction rate constant , medicinal chemistry , group (periodic table) , organic chemistry , catalysis , physics , quantum mechanics
The mechanisms of the homogeneous, unimolecular, gas‐phase elimination kinetics of several methyl ω ‐chloroesters were examined by using the ‘ ab initio ’ and DFT level of theories. Theoretical calculations of dehydrochlorination of methyl 3‐chloropropionate suggest a planar concerted, non‐synchronous, four‐membered cyclic transition state to give methyl acrylate. However, the parallel competitive gas‐phase elimination of methyl 4‐chlorobutyrate and methyl 5‐chlrovalerate occurs through neighboring group participation to render methyl chloride and the corresponding lactone through a concerted, semi‐polar five‐ and six‐membered cyclic transition state type of mechanism. Calculated thermodynamic and kinetic parameters reasonably agree with the experimental values at DFT B3LYP/6‐31G* theory level. Geometrical parameters, NBO charges and bond indexes showed strong polarization at C δ + ···Cl δ − bond in the transition state suggesting the breaking of CCl bond as rate‐determining factor for both dehydochlorination and lactone formation reactions. The synchronicity parameters suggest a concerted polar mechanism implying a TS which has ion‐pair character for lactone product formation. Copyright © 2008 John Wiley & Sons, Ltd.