Solvent Effects on the Stereoselectivity of Reaction of Methyl Acrylate, Methyl Methacrylate and Methyl trans-Crotonate with Cyclopentadiene: A Computational Study

The stereoselectivity of reaction of methyl acrylate, methyl methacrylate and methyl transcrotonate with cyclopentadiene was studied with ab initio RHF/6-31G* and B3LYP/6-31G* levels of theory. The stereoselectivities predicted for methyl acrylate and methyl methacrylate with cyclopentadiene in the gas phase were found to be in good agreement with experimental results. The preference of endo selectivity in solvents was more pronounced for methyl acrylate, however, the preference for the exo-addition for methyl methacrylate was predicted to be reduced in solvents. The solvent calculations predicted the endo- preference for methyl trans-crotonate in agreement with the experimental observations. The lower endo selectivity for methyl trans-crotonate with cyclopentadiene seems to be governed by the degree of asynchronicity of endo- and exo-transition states in water. B3LYP/6-31G* calculated activation enthalpy was found to be in good agreement with the observed activation enthalpy for methyl acrylate and cyclopentadiene, however, this method does not predict the stereoselectivities correctly in all cases. The hydrogen bonding between water and polarized transition states seems to be important for rate acceleration in wate

The S66 noncovalent interactions benchmark reconsidered using explicitly correlated methods near the basis set limit

The S66 benchmark for noncovalent interactions has been re-evaluated using explicitly correlated methods with basis sets near the one-particle basis set limit. It is found that post-MP2 "high-level corrections" are treated adequately well using a combination of CCSD(F12*) with (aug-)cc-pVTZ-F12 basis sets on the one hand, and (T) extrapolated from conventional CCSD(T)/heavy-aug-cc-pV{D,T}Z on the other hand. Implications for earlier benchmarks on the larger S66x8 problem set in particular, and for accurate calculations on noncovalent interactions in general, are discussed. At a slight cost in accuracy, (T) can be considerably accelerated by using sano-V{D,T}Z+ basis sets, while half-counterpoise CCSD(F12*)(T)/cc-pVDZ-F12 offers the best compromise between accuracy and computational cost.Comment: Australian Journal of Chemistry, in press [Graham S. Chandler special issue

Benchmark ab Initio Conformational Energies for the Proteinogenic Amino Acids through Explicitly Correlated Methods. Assessment of Density Functional Methods

The relative energies of the YMPJ conformer database of the 20 proteinogenic amino acids, with N- and C-termination, have been re-evaluated using explicitly correlated coupled cluster methods. Lower-cost ab initio methods such as MP2-F12 and CCSD-F12b actually are outperformed by double-hybrid DFT functionals; in particular, the DSD-PBEP86-NL double hybrid performs well enough to serve as a secondary standard. Among range-separated hybrids, ωB97X-V performs well, while B3LYP-D3BJ does surprisingly well among traditional DFT functionals. Treatment of dispersion is important for the DFT functionals; for the YMPJ set, D3BJ generally works as well as the NL nonlocal dispersion functional. Basis set sensitivity for DFT calculations on these conformers is weak enough that def2-TZVP is generally adequate. For conformer corrections to heats of formation, B3LYP-D3BJ and especially DSD-PBEP86-D3BJ or DSD-PBEP86-NL are adequate for all but the most exacting applications. The revised geometries and energetics for the YMPJ database have been made available as Supporting Information and should be useful in the parametrization and validation of molecular mechanics force fields and other low-cost methods. The very recent dRPA75 method yields good performance, without resorting to an empirical dispersion correction, but is still outperformed by DSD-PBEP86-D3BJ and particularly DSD-PBEP86-NL. Core−valence corrections are comparable in importance to improvements beyond CCSD(T*)/cc-pVDZ-F12 in the valence treatment

Assessment of CCSD(T)-F12 Approximations and Basis Sets for Harmonic Vibrational Frequencies

We consider basis set convergence and the effect of various approximations to CCSD­(T)-F12 for a representative sample of harmonic frequencies (the HFREQ2014 set). CCSD­(T*)­(F12*)/cc-pVDZ-F12 offers a particularly favorable compromise between accuracy and computational cost: its RMSD <3 cm^–1 from the valence CCSD­(T) limit is actually less than the remaining discrepancy with the experimental value at the valence CCSD­(T) limit (about 5 cm^–1 RMSD). CCSD­(T)-F12a and CCSD­(T)-F12b appear to benefit from error compensation between CCSD and (T)

Borazine as a sensor for fluoride ion: a computational and experimental study

The computational and experimental studies have revealed that even simple molecule like borazine can act as a sensor for fluoride ions. This study further reported the various binding modes of analytes using quantum chemical calculations and the nature of such interactions have been examined using electron density surface analysis. Total charge transfer analysis (qCT) correlates well with the binding affinities of analytes with the borazine receptor

The S66 non-covalent interactions benchmark reconsidered using explicitly correlated methods near the basis set limit

The S66 benchmark for noncovalent interactions has been re-evaluated using explicitly correlated methods with basis sets near the one-particle basis set limit. It is found that post-MP2 'high-level corrections' are treated adequately well using a combination of CCSD(F12*) with (aug-)cc-pVTZ-F12 basis sets on the one hand, and (T) extrapolated from conventional CCSD(T)/heavy-aug-cc-pV{D,T}Z on the other hand. Implications for earlier benchmarks on the larger S66x8 problem set in particular, and for accurate calculations on noncovalent interactions in general, are discussed. At a slight cost in accuracy, (T) can be considerably accelerated by using sano-V{D,T}Z+ basis sets, while half-counterpoise CCSD(F12*)(T)/cc-pVDZ-F12 offers the best compromise between accuracy and computational cost

Benchmark <i>ab Initio</i> Conformational Energies for the Proteinogenic Amino Acids through Explicitly Correlated Methods. Assessment of Density Functional Methods

The relative energies of the YMPJ conformer database of the 20 proteinogenic amino acids, with N- and C-termination, have been re-evaluated using explicitly correlated coupled cluster methods. Lower-cost <i>ab initio</i> methods such as MP2-F12 and CCSD-F12b actually are outperformed by double-hybrid DFT functionals; in particular, the DSD-PBEP86-NL double hybrid performs well enough to serve as a secondary standard. Among range-separated hybrids, ωB97X-V performs well, while B3LYP-D3BJ does surprisingly well among traditional DFT functionals. Treatment of dispersion is important for the DFT functionals; for the YMPJ set, D3BJ generally works as well as the NL nonlocal dispersion functional. Basis set sensitivity for DFT calculations on these conformers is weak enough that def2-TZVP is generally adequate. For conformer corrections to heats of formation, B3LYP-D3BJ and especially DSD-PBEP86-D3BJ or DSD-PBEP86-NL are adequate for all but the most exacting applications. The revised geometries and energetics for the YMPJ database have been made available as Supporting Information and should be useful in the parametrization and validation of molecular mechanics force fields and other low-cost methods. The very recent dRPA75 method yields good performance, without resorting to an empirical dispersion correction, but is still outperformed by DSD-PBEP86-D3BJ and particularly DSD-PBEP86-NL. Core–valence corrections are comparable in importance to improvements beyond CCSD­(T*)/cc-pVDZ-F12 in the valence treatment