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

摘要

Proučavana je stereoselektivnost metil akrilata, metil metakrilata i metil trans-krotonata s ciklopentadienom primjenom ab initio RHF/6-31G~* i B3LYP/6-31G~* nivoa teorije. Predviđena stereoselektivnost za metil akrilat i metil metakrilat s ciklopentadienom u plinskoj fazi je u dobrom slaganju s eksperimentalnim rezultatima. Prioritetnost endo-selektivnosti u otopini je izraženija za metil akrilat, dok je prioritetnost egzo-adicije metil metakrilata u otopini smanjena. Računi u otopini predviđaju endo-prioritetnost za metil trans-krotonat u skladu s eksperimentalnim opažanjima. Smanjena endo-selektivnost metil trans-krotonata s ciklopentadienom čini se da je utvrđena stupnjem asinhroniteta endo- i egzo-prijelaznih stanja u vodi. Aktivacijske entalpije izračunate na B3LYP/6-31G~* razini teorije su u dobrom slaganju sa opaženim aktivacijskim entalpijama metil akrilata i ciklopentadiena, no ova metoda ne predviđa stereoselektivnost na ispravan način u svim slučajevima. Stvaranje vodikove veze između molekula vode i polariziranih prijelaznih stanja ima važnu ulogu za ubrzavanje reakcija u vodi.%The stereoselectivity of reaction of methyl acrylate, methyl methacrylate and methyl trans-crotonate 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 water.