Rodolfo Moreno-Fuquen

4-Hydroxy-2,5-dimethylphenyl-benzophenone: Conformational stability, FT-IR and Raman investigation

In this paper we have studied the 4-hydroxyl-2,5 dimethylphenyl-benzophenone. Also, it was analyzed the vibrational assignment (FT-IR and Raman) in conjunction with computational results. The conformational analysis showed three barrier heights where two are due to the dihedral rotation and the other one is attributed to hydroxyl rotation. While the high dihedral rotational barrier (TS1) is 6.06-7.22 kcal mol(-1), the lower one (TS2) is almost three times smaller. The variations with the change of basis set is 5-8% to TS1, and 3-15% in the values predicted to TS2. In the case of OH rotational barrier, the values range from 3.70 to 4.86 kcal mol(-1), and it is also observed that this transition state is less sensitive to the change of basis set and to the method. Two isomers was detected due to the changes in the OH rotation with the gap energy lower than 0.7 kcal mol(-1), and at this point is seen that semi-empirical methods fail into describe the most stable conformation which may be due to the small energy gap. The enthalpy formation at 0 K and 298 K was 111.71 and 102.20 kcal mol(-1), respectively.

Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach

The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11 kcal·mol(-1)), with barrier heights ranging from 16 to 19 kcal·mol(-1). In contrast, the barrier energies on the keto/enol isomerization are almost 10 kcal·mol(-1) higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed.

2,4,6-Trinitrophenyl 3-methylbenzoate

In the title benzoate derivative, C14H9N3O8, the benzene rings form a dihedral angle of 87.48 (5)°. The central ester unit forms an angle of 19.42 (7)° with the methylbenzene ring, indicating a significant twist. In the crystal, the molecules are linked by weak C—H⋯O interactions forming a helical chain along [010].

2-Bromo-2-methyl-N-(4-nitrophenyl)propanamide

The title compound, C10H11BrN2O3, exhibits a small twist between the amide residue and benzene ring [the C—N—C—C torsion angle = 12.7 (4)°]. The crystal structure is stabilized by weak N—H⋯O, C—H⋯Br and C—H⋯O interactions. These lead to supramolecular layers in the bc plane.

4-{2-[4-(Dimethyl-amino)phen-yl]ethyl-idene}benzonitrile.

In the crystal of the title compound, C17H16N2, molecules are linked by C—H⋯N hydrogen bonds, forming rings of graph-set motifs R 2 1(6) and R 2 2(10). The title molecule is close to planar, with a dihedral angle between the aromatic rings of 0.6 (1)°. Torsion angles confirm a conformational trans structure.

4-Formyl-2-nitro­phenyl 4-bromo­benzoate

In the title compound, C14H8BrNO5, the benzene rings form a dihedral angle of 62.90 (7)°. The central ester group is twisted away from the nitro-substituted and bromo-substituted rings by 71.67 (7) and 8.78 (15)°, respectively. The nitro group forms a dihedral angle of 7.77 (16)° with the benzene ring to which it is attached. In the crystal, molecules are linked by weak C—H⋯O interactions, forming C(12) chains which run along [001]. Halogen–halogen interactions [Br⋯Br = 3.523 (3) Å] within the chains stabilized by C—H⋯O interactions are observed.

Imidazole-imidazolium picrate monohydrate.

The asymmetric unit of the title compound, C3H5N2 +·C6H2N3O7 −·C3H4N2·H2O or H(C3H4N2)2 +·C6H2N3O7 −·H2O, contains a diimidazolium cationic unit, one picrate anion and one molecule of water. In the crystal, the components are connected by N—H⋯O, N—H⋯N and O—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). In addition, weak intermolecular C—H⋯O hydrogen bonds lead to the formation of a three-dimensional network featuring R 5 5(19) rings.

A mechanistic study of the ammonolysis of alkyl acetoacetates in water. Formation of 1,5-dimethyl-2,6,9- triazabicyclo[3.3.1]nonane-3,7-dione as the main product

Ammonolysis of alkyl acetoacetates with 15% NH3 in water at room temperature initially lead to formation of alkyl β-aminocrotonates which slowly converted into 1,5-dimethyl-2,6,9-triaza-bicyclo[3.3.1]nonane-3,7-dione as the main product.

Pyridine N-oxide and 4-nitrophenol (1:1 complex)

In the title hydrogen-bonded complex, C 5 H 5 NO.C 6 H 5 -NO 3 , the two components are linked by an O-H...O hydrogen bond between the phenol hydroxyl group and the N-oxide O atom [O...O 2.553(2) A]. The interplanar angle between the aromatic rings in the two components is 41.29 (6)°.

1:1 Complex Formed by 2-Picoline N-Oxide and 4-Nitrophenol

The 2-picoline N-oxide and 4-nitrophenol moieties in the title complex, C 6 H 7 NO.C 6 H 5 NO 3 , are held together by an intermolecular O-H...CN hydrogen bond. This crystal structure exhibits partial overlap between the rings of the molecules, in the [110] direction. The complex formed may be described by two planes which contain the 2-picoline N-oxide and 4-nitrophenol molecules, respectively.