Damanjit Kaur

Theoretical studies on electron delocalisation in selenourea

Ab initio and density functional calculations have been performed on the different possible structures of selenourea(su), urea(u) and thiourea(tu) to understand the extent of delocalisation in selenourea in comparison to urea and thiourea. Selenourea(su-1) withC2 symmetry has the minima on the potential energy surface at MP2(fu)/6-31+G* level. The C-N rotational barrier in selenourea is 8.69 kcal/mol, which is 0.29 and 0.11 kcal/mol more than that of urea and thiourea respectively at MP2(fu)/6-31+G* level. N-inversion barrier is 0.55 kcal/mol at MP2(fu)6-31+G* level. NBO analysis has been carried out to understand the nature of different interactions responsible for the electron delocalisation.

N-inversion and C–N rotational barriers in HX=CH-NH2 (X=N,P,As) compounds: an ab initio study

Abstract Ab initio calculations at HF/6-31G* and MP2/6-31G* levels are performed on methanimidamide, 1-phosphinidene methanamine and 1-arsenidene methanamine in their E and Z conformations. All of them are found to have pyramidal arrangement around nitrogen of the amino group. Pyramidalization in the amino group could be identified only after including electron correlation. The N-inversion barrier and the C–N rotational barriers in these molecules have been calculated to understand the electron distribution in these molecules. The C–N bond length decreases, bond strength increases, N-inversion barrier decreases, C–N rotation barrier increases, flow of charge from N to X increases in the order methanimidamide

Theoretical study on O⋯Br and O⋯Cl halogen bonds in some small model molecular systems

AbstractHalogen bonding interactions of type X⋯O=C are important in various fields including biological systems. In this work, theoretical calculations were carried out using B3LYP/6-31 ++G**, MP2/6-31 ++G** and MP2/aug-cc-pVDZ methods on a series of O⋯X halogen bonds between CH2O and CH3CHO as halogen bond acceptor with X-Y (X = Cl, Br; Y = CF3, CF2H, CFH2, CN, CCH, CCCN) as halogen bond donors. The strength of interaction energy for O⋯Br halogen-bonded complexes varies from −2.16 to −5.26 kcal/mol while for O⋯Cl complexes, it is between −1.65 to −3.67 kcal/mol, which indicate the O⋯Br bond to be stronger in comparison to O⋯Cl bond. SAPT analysis suggests that the strength of halogen bonding arises from the electrostatic and induction forces while dispersion is playing a comparatively smaller role. The halogen-bonded interaction energies were found to correlate well with positive electrostatic potential VS,max, halogen bonded distances, and the change in s-character of C-X bond. The halogen-bonded interaction energies were also evaluated for O⋯I bonded complexes and thus these complexes were found to be stronger than O⋯Br and O⋯Cl bonded complexes. Graphical AbstractTheoretical calculations were carried out on halogen bonded complexes CH2O⋯X-Y and CH3CHO⋯X-Y (X = Cl, Br, I; Y = CF3, CF2H, CFH2, CN, CCH, CCCN). The interaction energies increase in the order O⋯Cl < O⋯Br < O⋯I. The interaction energies were found to be correlate well with the VS,max, halogen bonded distances, and the change in s-character of C-X bond.

Effect of sodium acetate and magnesium acetate on the solution behavior of some amino acids in water at 298.15 K : A compressibility approach

Apparent molar adiabatic compressibility, K2,φ,S, of glycine, DL-α-alanine, DL-α-amino-n-butyric acid, L-leucine and L-phenylalanine in water and in (0.5, 1.0, 2.0, 4.0, 5.5 mol kg−1) aqueous sodium acetate and in (0.5, 1.0, 1.5, 2.0 mol kg−1) aqueous magnesium acetate solutions has been determined from sound velocity, u, measurements at 298.15 K. The partial molar adiabatic compressibilities at infinite dilution, K02,S, obtained from K2,φ,S data have been used to calculate the corresponding partial molar adiabatic compressibilities of transfer at infinite dilution, ΔtK02,S, from water to aqueous sodium acetate and magnesium acetate (cosolutes) solutions. The ΔtK02,S values are positive for the studied amino acids in case of both the cosolutes and the values increase with the increase of the concentrations of both the cosolutes. The trends of ΔtK02,S have been rationalized in terms of the hydration of hydrophilic and hydrophobic parts of the amino acids studied. The interaction coefficients and hydration number, nH, have also been calculated and are discussed in terms of the dehydration effect of sodium acetate and magnesium acetate upon the amino acids in solutions. Attempt has been made to correlate these results with the earlier reported volumetric and viscometric studies for the same systems.

Theoretical study on the nature of S···H and O ··· H hydrogen bonds

Hydrogen bond acceptor ability of sulfur and oxygen has been analyzed in the adducts of dimethyl sulfide ((CH3)2S) and dimethyl ether ((CH3)2O) with H2O, CH3OH, HCOOH, NH2OH, CH3NH2, NH2NH2, HCONH2, HF and HCl. The stabilization energies have been evaluated using MP2/aug-cc-pVDZ, B3LYP/aug-cc-pVDZ, gaussian2 (G2) and complete basis set (CBS) theoretical levels. The contributors to stabilization energies are explored by employing symmetry adapted perturbation theory analysis, natural bond orbital analysis in addition to molecular orbital methods. Electrostatic component is the major contributor toward stabilization energy in both the type of adducts involving (CH3)2S and (CH3)2O which has been assigned to secondary electrostatic interactions. The second important contributor to comparable stabilization energies in the two series is the repulsive Eexch component which is relatively higher in adducts of (CH3)2O because of the relatively longer proximity of the monomeric units arising from smaller size of oxygen. GRAPHICAL ABSTRACT

Theoretical Characterization of Hydrogen Bonding Interactions between RCHO (R = H, CN, CF3, OCH3, NH2) and HOR′(R′ = H, Cl, CH3, NH2, C(O)H, C6H5)

AbstractIn this work, density functional theory and ab initio molecular orbital calculations were used to investigate the hydrogen bonded complexes of type RCHO ⋯HOR′ (R = H, CN, CF 3, OCH 3, NH 2, R′ H, Cl, CH 3, NH 2, C(O)H, C 6H 5) employing 6-31 ++g** and cc-pVTZ basis sets. Thus, the present work considers how the substituents at both the hydrogen bond donor and acceptor affect the hydrogen bond strength. From the analysis, it is reflected that presence of –OCH 3 and –NH 2 substituents at RCHO greatly strengthen the stabilization energies, while –CN and –CF 3 decrease the same with respect to HCHO as hydrogen bond acceptor. The highest stabilization results in case of (H 2N)CHO as hydrogen bond acceptor. The variation of the substituents at –OH functional group also influences the strength of hydrogen bond; nearly all the substituents increase the stabilization energy relative to HOH. The analysis of geometrical parameters; proton affinities, charge transfer, electron delocalization studies have been carried out. Graphical AbstractTheoretical calculations were carried out on the RCHO•••HOR’ (R = H, CN, CF3, OCH3, NH2; R’ = H, Cl, CH3, NH2, C(O)H, C6H5) hydrogen bonded complexes. The role of substituents on hydrogen donor and acceptor ability has been explored on the basis of analysis of geometrical data, proton affinities, NBO, AIM, SAPT, MESP and stabilization energies.

Theoretical studies on the conformations of selenamides

Ab initio HF/6-31+G*, MP2/6-31+G*, B3LYP/6-31+G* level calculations have been performed on HSe-NH2 to estimate the Se-N rotational barriers and N-inversion barriers. Two conformers have been found withsyn andanti arrangement of the NH2 hydrogens with respect to Se-H bond. The N inversion barriers in selenamide are 1.65, 2.47, 1.93 kcal/mol and the Se-N rotational barriers are 6.58, 6.56 and 6.12 kcal/mol respectively at HF/6-31+G*, MP2/6-31+G* and B3LYP/6-31+G* levels respectively. The nN →Σ *Se-H negative hyperconjugation is found to be responsible for the higher rotational barriers.

Hydrogen bonding of formamide, urea, urea monoxide and their thio-analogs with water and homodimers

AbstractAb initio and DFT methods have been employed to study the hydrogen bonding ability of formamide, urea, urea monoxide, thioformamide, thiourea and thiourea monoxide with one water molecule and the homodimers of the selected molecules. The stabilization energies associated with themonohydrated adducts and homodimers’ formation were evaluated at B3LYP/6-311++G** and MP2/6-311++G** levels. The energies were corrected for zero-point vibrational energies and basis set superposition error using counterpoise method. Atoms in molecules study has been carried out in order to characterize the hydrogen bonds through the changes in electron density and laplacian of electron density. A natural energy decomposition and natural bond orbital analysis was performed to understand the nature of hydrogen bonding. Graphical AbstractSixteen hydrogen bonded adducts of formamide, urea and urea monoxide with one water molecule and their homodimers have been optimized at B3LYP/6-311++G** and MP2/6-311++G** levels. Monohydrated Adducts and homodimers formation with the corresponding thio-analogs were also studied for comparative purpose. Atoms in molecules study has been carried out in order to characterize the hydrogen bonds. A natural energy decomposition and natural bond orbital analysis were performed to understand the nature of hydrogen bonding.

The explicit interactions of five-membered saturated heterocyclics containing one and two heteroatoms with single water molecule

In this article, the hydrogen bonding interaction between saturated five-membered heterocyclic molecules and water has been investigated. Molecular orbital and density functional theory methods have been used to evaluate the stabilization energies associated with the adduct formation between heterocyclic molecules and water. The hydrogen bond acceptor ability of O, S, Se, and N as members of five-membered ring has been analyzed. The effect of the presence of second heteroatom N in the ring on the hydrogen bond interaction has also been evaluated. Atoms in molecules theory calculations were carried out to characterize the hydrogen bond through the changes in electron density and Laplacian of electron density. A natural energy decomposition analysis and natural bond orbital analysis is also performed to understand the nature of hydrogen bonding interaction in monohydrated five-membered heterocyclic adducts.

Se–N interactions in selenohydroxylamine: a theoretical study

The potential energy surfaces of thiohydroxylamine HS–NH2, 1, and selenohydroxylamine HSe–NH2, 2, have been searched, using ab initio and density functional methods, to study the conformational preferences. There are two minima on the path of rotation around the Se–N bond in 2. High accuracy G2MP2 calculations showed that the Se–N rotational barrier in 2 is 5.41 kcal mol−1, which is 1.16 kcal mol−1 less than the S–N rotational barrier in 1. The inversion around N in 1 and 2 goes through low energy barriers of 1.79 and 2.44 kcal mol−1 at the same level respectively. Charge analysis using the natural population analysis (NPA) method has been performed to understand the electronic factors responsible for the observed trends in the Se–N interactions. The strength of the negative hyperconjugation in 2 has been estimated using natural bond orbital (NBO) analysis and by studying the substituent effect.