كليدواژه :
ab initio , Phthalimido , prolinamide , catalyst
چكيده فارسي :
Phthalimido-prolinamide (PP) was prepared from N-Boc-proline and N-aminophthalimide. It was developed for organocatalytic enantioselective direct aldol reactions of various aldehydes with ketones [1]. The use of 5 mol% of water accelerated the reaction and the α-hydroxy carbonyl product could be attained in high yields and high stereoselectivities. In this work, the structure, energetics and infra-red (IR) spectrum of PP were studied by ab initio electronic structure methods, namely, Møller–Plesset second-order perturbation theory (MP2) correlated consistent, aug-cc-pvDZ basis functions. Figure 1 and 2 represent the optimized structure and IR spectrum of the catalyst, respectivally. The longest peak in figure 2 refers to asymmetric stretch of the two carbony groups in the phthalimide part of the molecule. The active sites of molecule can be defined by analyzing the partial atomic charges. The mulliken charge of the oxygen in carbonyl group of proline component have been estimated -0.967 which is the highest negative value and the maximum posetive value refers to C atom in that carbonyl group. Molecules such as PP has several sites to accept proton. Proton transfer to these sites can lead to the production of stable protonated ions which may accelerate the reaction. In cases where there are more than one protonated ion, the concept of topical proton affinity (PA) arises. Topical PA as the negative of the enthalpy change of the proton transfer reaction were calculated at the DFT (B3LYP) level of theory with 6-311++G(g,p) basis set because of the extremely time consuming method of MP2 in this case. Gas phase basicity (GB) as the negative of the Gibbs free energy change of the proton transfer reaction is defined at the same level of theory. All of the computations were performed with Gaussian 09 package. The ionization energy and electron affinity can refer to vertical and adiabatic quantities. Vertical ionization energy (VIE) and vertical electron affinity (VEA) are calculated as electronic energy difference between the ground state of the neutral molecule and its cation and anion at the equilibrium geometry of neutral molecule, respectably. Adiabatic ionization energy (AIE) and adiabatic electron affinity (AEA) are defined as the energy difference between neutral molecules and referred ions in their relaxed geometry [2]. These values were estimated at the B3LYP/6-311++G(d,p) level of theory. The information of the amount of mentioned properties can be helpful in finding of the role of catalyst in mechanism of the reactions.
