A. Manimekalai

Conformational Studies of Somet(4)-Acetoxy-r(2),c(6)-diphenyl-N-acetylpiperidines Using1H NMR Spectra. Evidence for Contribution of Boat Forms with a Substituent in the Flagpole Position

The NOESY spectrum and vicinal coupling constants of t(4)‐acetoxy‐3,3‐dimethyl‐r(2),c(6)‐diphenyl‐N‐acetylpiperidine suggest that the compound adopts a chair conformation with axial phenyl groups. The vicinal coupling constants of t(4)‐acetoxy‐r(2),c(6)‐diphenyl‐N‐acetylpiperidine could be accounted for by an equilibrium mixture of the chair conformation with axial phenyl groups and a boat conformation with one phenyl group in the flagpole position. The vicinal coupling constants suggest that in the case of t(4)‐acetoxy‐t(3)‐methyl‐r(2),c(6)‐diphenyl‐N‐acetylpiperidine another boat conformation with the acetoxyl group in the flagpole position also makes some contribution and t(4)‐acetoxy‐t(3),t(5)‐dimethyl‐r(2),c(6)‐diphenyl‐N‐acetylpiperidine exists largely in a boat conformation with the acetoxyl group in the flagpole position. The flattened chair conformation, proposed earlier for the piperidine ring in N‐acetylsolasodine, has been shown to be incorrect and a boat conformation without allylic strain is assigned. The earlier interpretation of spectral results on N‐nitroso‐2α‐methyldecahydroquinoline is also re‐examined.

r-2,c-6-Bis(4-chloro-phen-yl)-t-3-isopropyl-1-nitro-sopiperidin-4-one.

In the title molecule, C20H20Cl2N2O2, the piperidine ring adopts a chair conformation and the nitroso group at position 1 has a bisectional orientation. The two benzene rings and the isopropyl group attached to the piperidine ring in positions 2, 6 and 3, respectively, have axial orientations. The dihedral angle between the two benzene rings is 21.56 (13)°. One of the Cl atoms is disordered over two positions in a 0.281 (5):0.719 (5) ratio. In the crystal structure, molecules are linked by C—H⋯O hydrogen bonds and a short C—H⋯O contact occurs within the molecule.

CONFORMATIONAL ANALYSIS OF SUBSTITUTED N-NITROSO-TRANS-DECAHYDROQUINOLIN-4-ONES

1H and 13C NMR resonance assignments and conformational assignments were carried out for four N‐nitroso‐2‐phenyl‐trans‐decahydroquinolin‐4‐ones. In addition to conventional 1D NMR methods, 2D shift‐correlated NMR techniques (1H–1H COSY, 1H–1H NOESY and 1H–13C HETCOR) were used for the signal assignments. At room temperature the title compounds exist in two isomeric forms. The preferred conformations of both the isomers of nitrosamines were determined by a comparison of the spectral data with those for the parent amines, and with the aid of substituent parameters. Molecular strain in nitrosamines is minimized by partial escape of the piperidine moiety into non‐chair conformation.

Computational and spectral studies of 6-phenylazo-3-(p-tolyl)-2H-chromen-2-one

6-Phenylazo-3-(p-tolyl)-2H-chromen-2-one 4 was prepared and characterized by IR, (1)H, and (13)C NMR spectral studies. The optimized structure of the chromen-2-one 4 was investigated by the Gaussian 03 B3LYP density functional method calculations at 6-31G(d,p) basis set. The gauge-independent atomic orbital (GIAO) (13)C and (1)H chemical shift calculations for the synthesized chromen-2-one in CDCl3 were also made by the same method. The computed IR frequencies of the chromen-2-one and the corresponding vibrational assignments were analyzed by means of potential energy distribution (PED%) calculation using vibrational energy distribution analysis (VEDA) program. The first order hyperpolarizability (βtot), polarizability (α) and dipole moment (μ) were calculated using 6-311G(d,p) basis set and the nonlinear optical (NLO) properties are also addressed theoretically. Stability of the chromen-2-one 4 molecule has been analyzed by calculating the intramolecular charge transfer using natural bond order (NBO) analysis. The molecular electrostatic potentials, HOMO-LUMO energy gap and geometrical parameters were also computed. Topological properties of the electronic charge density in chromen-2-one 4 were analyzed employing the Baders Atoms in Molecule (AIM) theory which indicated the presence of intramolecular hydrogen bond in the molecule.

DFT and experimental determination of conformations of 2-(ethoxycarbonylmethoxy)-5-(arylazo)benzaldehydes and their oximes

2‐(Ethoxycarbonylmethoxy)‐5‐(arylazo)benzaldehydes 1–4 and their oximes 5–8 were synthesized and characterized by IR, 1H and 13C NMR spectroscopy. The favoured conformations of aldehydes 1–4 and oximes 5–8 were predicted theoretically. Selected geometrical parameters and charges were derived from optimized structures. IR, 1H and 13C NMR data were also computed using Gaussian‐03 package and compared with the observed values. 15N and 17O chemical shifts were also determined theoretically. Copyright

Studies of some monocyclic and bicyclic arylacetonitriles

The high‐resolution 1H, 13C, 1H1H COSY and 1H13C COSY NMR spectra have been recorded in CDCl3 for arylacetonitriles 1–12 and analyzed. The arylacetonitriles 3–7 exist in two isomeric forms E (methyl group is anti to cyano group) and Z (the methyl group is syn to cyano group) in solution. Normal chair conformation with equatorial orientations of phenyl rings at C‐2 and C‐6 for monocyclic nitriles 1 and 2, epimeric chair structure EC (axial configuration of methyl group at C‐3) for both the E and Z isomers of arylacetonitrile derivatives (3–7) and a distorted boat form, B3, for the N‐acylacetonitrile derivatives (8–10) have been proposed based on NMR data. The bicyclic nitriles 11 and 12 exist in twin chair conformations in solution. DFT calculations and chemical shifts also support these conformations. Geometry optimizations for 1–12 were carried out according to density functional theory using B3LYP/6‐31G(d,p) basis set and for 1 and 8 the theoretical geometrical parameters have been compared with those of single crystal measurements. Copyright

DFT and experimental prediction of negative chemical shifts of methyl protons in some piperidines.

The high resolution (1)H NMR spectra of four 3-ethyl-4-hydroxy-4-phenylpiperidines 1-4 have been recorded in CDCl(3), C(6)D(6), and (CD(3))(2)CO and analysed. These compounds exist in chair conformation with axial orientation of hydroxyl group at C(4) and equatorial orientation of the remaining substituents. The chemical shifts of methyl protons of ethyl group are quiet novel and surprising and are closer to TMS in CDCl(3) and somewhat higher in C(6)D(6). Changing the solvent from CDCl(3) to (CD(3))(2)CO alters the chemical shifts of these protons and they are very closer to TMS (0.01 ppm) in 3-4 and negative in 2 i.e., less than zero. The results are interpreted in terms of the magnetic anisotropic effect of the phenyl rings at C(2) and C(4) which in turn depends on the conformations of the ethyl group at C(3) and hydroxyl group at C(4). DFT studies were also performed to predict the favoured conformations of ethyl group at C(3) and hydroxyl group at C(4). Chemical shifts were also computed theoretically in the favoured conformation and they also support negative chemical shifts of 2 in acetone-d(6).

t-3-Ethyl-r-2,c-6-bis­(2-fur­yl)piperidin-4-one

In the title molecule, C15H17NO3, the piperidine ring adopts a chair conformation. The dihedral angle between the two furyl rings is 72.4 (1)°. The ethyl group and the furyl rings have equatorial orientations. Molecules are linked by N—H⋯O hydrogen bonds.

t‐3‐Benzyl‐1‐formyl‐r‐2,c‐6‐diphenylpiperidin‐4‐one

The piperidine ring of the title compound, C25H23NO2, is in a distorted boat form. The phenyl ring at position 2 makes a dihedral angle of 80.6 (1)° with the phenyl ring of the benzyl group at position 3, and 61.2 (1)° with the phenyl ring at position 6. The dihedral angle between the phenyl ring of the benzyl group and the phenyl ring at position 6 is 84.2 (1)°. The formyl group and the phenyl ring at position 6 have equatorial orientations. The phenyl ring at position 2 and the benzyl group at position 3 have axial orientations. C—H⋯O and C—H⋯π hydrogen bonds are found in the crystal structure.

Synthesis, spectral and conformational studies of some N-arylsulfonyl-t(3)-isopropyl-r(2),c(6)-diarylpiperidin-4-ones.

A series of N‐arylsulfonyl‐t(3)‐isopropyl‐r(2),c(6)‐diarylpiperidin‐4‐ones 1–8 were synthesized and characterized unambiguously by 1H, 13C NMR, 2D‐COSY and HSQC NMR spectroscopy. The conformational preferences of 1–8 have been discussed on the basis of the coupling constants, and they suggest normal chair conformation with equatorial orientations of all the substituents in 1–8. The preferred conformation of aryl sulfonyl group at nitrogen and isopropyl group at C–3 was determined theoretically using density functional calculations. Copyright