Manuel F. Rubio

Study of the sulfur atom as hydrogen bond acceptor in N(2)-pyridylmethyl-N′-arylthioureas

The hydrogen acceptor capability of the sulfur atom in the biologically relevant N-2-pyridylmethyl-N′-arilthioureas was explored. N-2-Pyridylmethyl thioreas were selected to avoid the formation of intramolecular six-membered hydrogen-bonded ring. The compounds studied were N-2-pyridylmethyl-N′-phenylthiourea (1), N-2-pyridylmethyl-N′-2-methoxythiourea (2), N-2-pyridylmethyl-N′-4-methoxyphenylthiourea (3), and N-2-pyridylmethyl-N′-4-bromophenylthiourea (4). 1 crystallizes in the monoclinic space group P21/c, with a = 7.419(1) Å, b = 18.437(2) Å, c = 9.656(1) Å, β = 106.277(6)°, V = 1267.8(3) Å3, Z = 4. 2 crystallizes in the monoclinic space group P21/c, with a = 8.064(2) Å, b = 18.382(7) Å, c = 9.865(5) Å, β = 97.81(3)°, V = 1448.8(11) Å3, Z = 4. 3 crystallizes in the monoclinic space group P21/c, with a = 11.472(1) Å, b = 13.520(1) Å, c = 10.088(1) Å, β = 112.60(1)°, V = 1444.5(2) Å3, Z = 4. 4 crystallizes in the triclinic space group P-1, with a = 4.583(3) Å, b = 10.263(3) Å, c = 14.396(3) Å, α = 77.92(2)°, β = 88.55(4)°, γ = 80.02(4)°, V = 652.1(5) Å3, Z = 2. Both thiourea N–H groups form intermolecular hydrogen bonds, one with the thione sulfur atom and the other with the pyridine nitrogen atom but the H-bonding schemes are not the same maybe due to the flexibility of the molecules.

Ethyl and methylphenylcarbamates as antihelmintic agents: theoretical study for predicting their biological activity by PM3

Abstract PM3 calculations have been carried out on alkyl 4-(R)-phenylcarbamates and benzimidazole compounds in order to identify electronic features similitude using Principal Component Analysis, Canonic Analysis, stepwise Multiple Regression and Cluster Analysis. We have been able to establish a trend to predict antihelmintic activity for the best candidates of alkyl 4-(R)-phenylcarbamates.

Intra- vs intermolecular hydrogen bonding. The crystal structure of 5-methyl-2-hydroxyacetophenone thiosemicarbazone monohydrate and salicylaldehyde-2-methylthiosemicarbazone monohydrate

The crystal structure of 5-methyl-acetophenonethiosemicarbazone monohydrate,A, and salicylaldehyde-2-methylthiosemicarbazone monohydrate,B, were determined using single crystal X-ray diffraction.A crystallizes in the monoclinic space groupC2/c, with lattice parametersa=14.161(2),b=15.753(1) Å,c=11.084(1) Å, β=112.59(1)° andZ=4, yielding a calculated density ofDcalc=1.352 mg/m3.B crystallizes in the triclinic space groupP1, witha=7.233(2) Å,b=7.371(2) Å,c=11.841(2) Å, α=82.77(2)°, β=78.33(2)°, γ=63.06(2)° andDcalc=1.371 mg/m3 forZ=2,. In bothA andB the immine nitrogen and the sulfur atom areanti with respect to N2-C8. WhileA presents the usual intramolecular six membered hydrogen bond ring,B has instead an intermolecular hydrogen bond between the hydroxy moiety of the salicyladehyde and a water molecule. AM1 calculations agree with the experimental conformations observed in both compounds.

MECHANISM OF REARRANGEMENT OF OXIDES OF TERTIARY AMINES. BEHAVIOR OF THE MOLECULAR ORBITALS

Abstract The study of the mechanism of rearrangement of oxide of a tertiary amine to the O-substituted hydroxylamine was carried out by the semiempirical method AM1. The case of the N-oxide of N-(2,4-dinitrophenyl) piperidine was taken as a model. The study of the reaction mechanism was performed taking into account the presence or lack of an intermolecular hydrogen bond with formic acid, analyzing the behavior of the frontier molecular orbitals and their neighbors. We have also made ab initio calculations in the vicinity of the transition state previously calculated with AM1 using the basis STO-3G and 3–21G∗.

A new model for the theoretical tautomeric constant (KT) calculation of 2-, 3- and 4-substituted pyridines☆

Abstract AM1, PM3, HF/STO-3G, HF/3-21G ∗ , HF/6-31G ∗ , MP2/STO-3G//HF/STO-3G, MP2/3-21G ∗ //HF/3-21G ∗ and MP2/6-32G ∗ //HF/6-31G ∗ calculations and the Boltzmann distribution law were used to establish a new model for the calculation of the tautomeric constant ( K T ) of 2-, 3- and 4-substituted pyridines in both gas and solution phase. The solvent effect was approximated with one water molecule around each tautomeric species. Three mathematical models were used to calculate the K T values. A linear correlation was carried out to show that some results were similar to the experimental ones.

REARRANGEMENT OF 2,3-DIHYDRO-1,2-DIAZEPIN-4-OL. BEHAVIOR OF THE MOLECULAR ORBITALS'

Abstract Our research was carried out by AM1 semiempirical calculations in order to show the reaction mechanism of the rearrangement of 2,3-dihydro-1,2-diazepin-4-ol to 8-oxa-1,2-diazabicyclo[3.2.1]octene. We will show three different routes for these rearrangements. The molecular reactivity was established starting from the molecular orbitals, mainly the frontier molecular orbitals and some of their neighbors.

A proposal for a oxycyclobuta Cope aromatic rearrangement of cis-1-cyano-1(4-methyl-3-methoxyphenyl)-2-isopropenyl-cyclobutane. AM1 study ☆

Abstract AM1 calculations were carried out to study the oxycyclobuta Cope aromatic rearrangement of the cis -1-cyano-1(4-methyl-3-methoxyphenyl)-2-isopropenyl-cyclobutane system. Eight possible pathways were analyzed for explaining this rearrangement (four conrotatory motions and four disrotatory motions). The results indicate that the reaction mechanism involves a tricyclic intermediate.

About perezone derivatives, a theoretical approach

Abstract Theoretical AM1 calculations were carried out on 12 derivatives of perezone. The results yield 3 different resonance forms of the diradical configuration for the triplet state. The frontier molecular orbitals in the ground state were compared with the SOMOs in the triplet state in the process of formation of the diradical.

A proposal for the prediction of the isomeric formation of N,N-di(2-acetylcyclopentyl) ethylenediamine

Abstract AM1 calculations were carried out to study the reaction mechanism required for obtaining N,N-di(2-acetylcyclopentyl) ethylenediamine. A proposal of the reaction mechanism showed that the decisive step of the reaction is the addition of the second molecule of 2-acetylcyclopentyl. Starting from this result, a mathematical model was tested by using the formation energy, the Boltzmann Distribution Law and the percentages of nucleophilic and electrophilic characters calculated with AM1 and PM3, and STO-3G, 3-21G∗ and 6-31G∗ basis. According to this model, the AM1 calculations predict the experimental results best. The populations of the products were also calculated, once having been obtained experimentally, with the levels AM1 and PM3 as the starting point; again, the calculations carried out with AM1 were found to predict the experimental results better than the PM3 method.