TY - JOUR
T1 - Trajectory studies of SN2 nucleophilic substitution. 5. Semiempirical direct dynamics of cl- - - -CH3Br unimolecular decomposition
AU - Peslherbe, Gilles H.
AU - Wang, Haobin
AU - Hase, William L.
PY - 1996
Y1 - 1996
N2 - Direct dynamics simulations of the dynamics of the Cl- - - -CH3Br complex are performed for 25 ps or until either Cl- + CH3Br or ClCH3 + Br- are formed. Two different potential energy surfaces, AM1-SRP1 and AM1-SRP2, are investigated in the simulations by using the AMI semiempirical model with two different sets of specific reaction parameters (SRPs). The AM1-SRP surfaces give non-RRKM unimolecular dynamics for Cl- - - - CH3Br as found in a previous simulation based on an analytic potential energy surface, PES1(Br), derived by fitting HF/SV4PP/6-31G* ab initio calculations and experimental data. However, detailed aspects of the Cl-- - -CH3Br intramolecular and unimolecular dynamics are different for the two AM1-SRP surfaces and in some cases strikingly different from those found for the PES1 (Br) surface. Global potential energy surface properties, not only those of stationary points and along the reaction path, are expected to influence the Cl-- - -CH3Br nonstatistical dynamics. Of the three surfaces, only PES1(Br) gives a relative translation energy distribution for the ClCH3 + Br- dissociation products which agrees with experiment. The average product translational energy is approximately a factor of 3 too large for each of the AM1-SRP surfaces. A definitive determination of all the dynamics and kinetics for Cl- + CH3Br → ClCH3 + Br- SN2 nucleophilic substitution may require dynamical calculations based on a potential energy surface derived from high-level ab initio calculations.
AB - Direct dynamics simulations of the dynamics of the Cl- - - -CH3Br complex are performed for 25 ps or until either Cl- + CH3Br or ClCH3 + Br- are formed. Two different potential energy surfaces, AM1-SRP1 and AM1-SRP2, are investigated in the simulations by using the AMI semiempirical model with two different sets of specific reaction parameters (SRPs). The AM1-SRP surfaces give non-RRKM unimolecular dynamics for Cl- - - - CH3Br as found in a previous simulation based on an analytic potential energy surface, PES1(Br), derived by fitting HF/SV4PP/6-31G* ab initio calculations and experimental data. However, detailed aspects of the Cl-- - -CH3Br intramolecular and unimolecular dynamics are different for the two AM1-SRP surfaces and in some cases strikingly different from those found for the PES1 (Br) surface. Global potential energy surface properties, not only those of stationary points and along the reaction path, are expected to influence the Cl-- - -CH3Br nonstatistical dynamics. Of the three surfaces, only PES1(Br) gives a relative translation energy distribution for the ClCH3 + Br- dissociation products which agrees with experiment. The average product translational energy is approximately a factor of 3 too large for each of the AM1-SRP surfaces. A definitive determination of all the dynamics and kinetics for Cl- + CH3Br → ClCH3 + Br- SN2 nucleophilic substitution may require dynamical calculations based on a potential energy surface derived from high-level ab initio calculations.
UR - http://www.scopus.com/inward/record.url?scp=0029984654&partnerID=8YFLogxK
U2 - 10.1021/ja953120t
DO - 10.1021/ja953120t
M3 - Article
AN - SCOPUS:0029984654
SN - 0002-7863
VL - 118
SP - 2257
EP - 2266
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 9
ER -