On the Factors Affecting H-Bonding : A CCSD(T) // B3LYP Study on Malonaldehyde Cation-Radical

Abstract

Among the factors that may affect H-bond strength, the effect of the molecular ionization has not received any considerable attention. Here, malonaldehyde and its cation-radical as models were studied using DFT (B3LYP) and ab-initio theories (HF, MP2, and CCSD(T)). Based on establishing a comparison with the CCSD(T)/CBS energy barrier (from literature), we have found that the CCSD(T)/D95(d,p)//B3LYP/6-31G(d,p) computational protocol can be used as a reference for evaluating performance of the B3LYP and the MP2 methods on this model. In this computational organic chemistry study several aspects were investigated, they are: structures, energies, natural population analysis (NPA) charges, intramolecular charge transfer (delocalization) energies, and atoms in molecule (AIM) electron densities with regard to the Hbonding. The results indicate that loss of an electron can cause considerable effects on the various electronic structure aspects and the details are presented and discussed. All the aspects confirm that ionizing the molecule disturbs the electron density distribution in the HOMO orbital and makes the two oxygen atoms, relatively, electron deficient centers which consequently weakens both the H1-O1 bond and the O2/H1-O1 H-bond. The details of this investigation are new addition to the hydrogen bond theory. Other types of molecular models and computational protocols are of interest for future investigations.

Toward Exploring Novel Organic Materials: MP4-DFT Properties of 4-Amino-3-Iminoindene

“…The nature of stimuli-2 depends on the operating temperature. A support to the values of the proton transfer activation energies comes from the CCSD(T)/D95(d,p)//B3LYP/6-31G(d,p) and QCISD(T)/D95(d,p)//B3LYP/6-31G(d,p) protocols, as recommended earlier [ 14 , 18 ]. In a previous work, we demonstrated that, for a specific molecular system, tautomerism is a controllable process [ 32 ].…”

“…The availability of this value allows searching for less demanding alternative methods. Previously, we found that both B3LYP/6-31++G(3df,3pd) and MP2/6-31++G(3df,3pd) protocols fail in predicting the proton transfer activation energy of malonaldehyde [ 18 ]. Table 1 presents the results of various basis set types along with the MP4(SDTQ) method.…”

“…The MP4(SDTQ)/6-31G(d,p) level of theory value is equal to 4.11 kcal/mol, which is an excellent estimation compared to the more demanding CCSD(T) [ 18 ] and the quadratic configuration interaction with single and double excitations and an approximation of the triples; QCISD(T) [ 14 ], protocols. Further evaluation of the MP4(SDTQ)/6-31G(d,p)//B3LYP/6-31G(d,p) protocol was performed on six malonaldehyde derivatives ( Figure 2 C, Table 2 ) where the reference values are focal point (FP) CCSD(T) energies [ 31 ].…”

“…As recommended earlier [ 18 ], the Becke, three-parameter, Lee-Yang-Parr exchange-correlation functional B3LYP [ 19 , 20 ] and the 6-31G(d,p) basis set [ 21 ] were used to optimize all of the geometries. These calculations gave real frequencies for 1-AII and 2-AII, which indicates that each is a true minimum.…”

Unique and Novel Hydrogen Bonding at the Frontiers: 2-Dimethylaminobenzoic Acid and MFn Interaction as Model

“…The Gaussian 03 29 was used for all the calculations. The B3LYP/6-31G(d,p)-SDD protocol was employed as recommended earlier [30][31][32] for the geometry optimization and the frequency calculations. The B3LYP functional is composed of the Becke three parameter exchange functional 33 , the non-local correlation provided by Lee, Yang, and Parr (LYP) 34,35 , and local correlation functional (III) developed by Vosko, Wilk, and Nusair (VWN) 36 .…”