Luis Carballeira

Conformational analysis of polyfunctional amino compounds by molecular mechanics.: Part II. 1,2-Ethanediamine, 1,3-propanediamine and 1,4-diazacyclohexanes

Abstract The molecular mechanics program developed by Allinger (MM2) has been applied to the conformational analysis of two classes of compounds including NC⋯CN structures: linear diazacompounds and 1,4-diazacyclohexanes. The predictions for the linear compounds (1,2-ethanediamine and 1,3-propanediamine) agree qualitatively with available experimental data and also, in general, with the most reliable ab initio calculations. The results for the cyclic compounds agree quite well with experimental geometrical and energy data derived from electron diffraction and NMR studies respectively.

Conformational analysis of polyfunctional aminic compounds by molecular mechanics: Part I. Methanediamines and 1,3-diazacyclohexanes

Abstract The molecular mechanics method developed by Allinger (MM2) has been applied to the conformational analysis of two classes of compounds including NCN structures: linear 1,3-diazacompounds and 1,3-diazacyclohexanes. The conformational equilibria and ring-inversion barriers predicted for the latter class agree satisfactorily with NMR data. The predictions for the linear compounds do not all agree with the results of previous ab initio calculations, but, in certain cases, are supported by experimental electron diffraction data.

Conformational analysis of bicyclic systems including the NCO unit by molecular mechanics: Part I. Perhydropyrido [1,2-c][1,3] oxazines

Abstract Perhydropyrido [1,2-c] [1,3] oxazine and some of its derivatives, all of which contain the NCO unit, were conformationally analysed using a molecular mechanics force field obtained from the MM285 field of Allinger. The results (energetic stabilities and geometries of the different conformers) were consistent with experimental data (NMR, X-ray and IR spectra, and dipole moments) available for these systems.

Ab initio studies of molecules with N-C-O units: Part I. Methylaminomethanol, 1-methoxymethylamine and 1-methoxy-N-N-dimethyl-methylamine

Abstract The conformations of various conformers of the molecules methylaminomethanol, 1-methoxymethylamine and 1-methoxy-N,N-dimethylmethylamine, all of which contain an N-C-O unit, were determined by an ab initio method using the 4-21G basis set and complete geometrical optimization. The results were interpreted in terms of anomeric interactions: the most stable conformers of all three molecules have their lone pairs antiperiplanar to their polar bonds.

Ab initio gradient conformational analysis of polyazocyclohexanes:1,4-diazocyclohexane, 1,3-diazocyclohexane and 1,3,5-triazocyclohexane

Abstract The chair conformations of 1,4-diazocyclohexane, 1,3-diazocyclohexane and 1,3,5-triazocyclo-hexane were determined by ab initio methods using the 4-21G basis set and complete geometrical optimization. The results are compared with available data from experimental and molecular mechanics studies.

Conformational analysis of bicyclic systems including the NCO unit by molecular mechanics: Part III. Perhydro-oxazolo [3,4-a] pyridine, perhydro- oxazolo [3,4-c] [1,3]oxazines and perhydro [1,3] oxazino [3,4-c] [1,3]oxazines

Abstract A conformational analysis was carried out on perhydro-oxazolo [3,4-a] pyridine and some perhydro-oxazolo- and perhydro [1,3] oxazino[3,4-c] [1,3]oxazines using a force field obtained from that of Tai and Allinger (MM285) (J. Am. Chem. Soc., 110 (1988) 2050) for the treatment of compounds with NC:O units. The results obtained were in good agreement with the experimental data available.

Conformational analysis of bicyclic systems including the NCO unit by molecular mechanics Part II. 4,5- and 5,6- Tetramethylene perhydro-1,3-oxazines

Abstract A conformational analysis of the 4,5- and 5,6-tetramethylene-perhydro-1,3-oxazines and some of their derivatives has been carried out using a force field obtained from one previously developed by Allinger (MM285). The results (energy stabilities and geometries) are consistent with the available experimental data.

AB initio studies of molecules with N-C-O units: Part 2. 1-oxa-3-azacyclohexane, 1-oxa-3,5-diazacyclohexane and 1,3-dioxa-5-azacyclohexane

Abstract Conformers of 1-oxa-3-azacyclohexane, 1-oxa-3,5-diazacyclohexane and 1,3-dioxa-5-azacy-clohexane were studied by an ab initio method using the 4–21G basis set and complete geometrical optimization. The results were interpreted in terms ofanomeric interactions, and the influence of the heteroatoms on ring planarity and the environments of the nitrogen atoms are discussed.

Ab Initio studies of molecules with N-C-O units: Part IV. N,N-dimethylaminomethanol, 2-amino-2-propanol and 1-methylaminoethanol

Abstract We have carried out an ab initio conformational 4-21G study with full optimization of the geometry of N , N -dimethylaminomethanol, 2-amino-2-propanol and 1-methylaminoethanol, all of which have the structural N-C-O unit. The results are interpreted in terms of the anomeric effect and compared with those already available for molecules including the N-C-O unit.

Conformational analysis of polyfunctional amino compounds by molecular mechanics: Part III. 1,3,5-Triazacyclohexanes, 2,5,7,10-tetrazabicyclo[4.4.0]-decanes and 1,3,5,7-tetrazabicyclo[3.3.1]nonanes

Abstract The molecular mechanics program of Allinger, MM2,has been applied to the conformational analysis of various cyclic and bicyclic compounds containing the NCN unit. The results have been compared with the available experimental data and with previous MM2 results for other cyclic amino compounds. It is found that the inclusion of more NCN units in the ring has no effect on the agreement between theory and experiment. Changes in ring geometry due to substitution and to increasing the number of nitrogen atoms have been analysed using Cremer-Poples ring-puckering coordinates.