The conformational analysis of saturated heterocycles. Part XLIX. The conformation of ring NH-groups in piperazines, hexahydropyrimidines, tetrahydro-1,3-oxazines, and tetrahydro-1,3-thiazines

Cook, M. J.; Jones, Richard A.; Katritzky, Alan R.; Manas, M. Moreno; Richards, A.; Sparrow, A. J.; Trepanier, D. L.

doi:10.1039/p29730000325

Cited by 17 publications

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“…Former studies, including a number of experimental conformational analysis works − and theoretical studies for N−CH 2 −N and N−N containing systems, , targeted the neutral form of structures ( 1 )−( 3 ) and related systems. Predicted p K a values for structures ( 2 ) and ( 3 ) are 10.04 ± 0.20 and 11.21 ± 0.20, respectively .…”

Section: Introductionmentioning

confidence: 99%

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Messer

2011

J. Phys. Chem. B

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For exploring the preferred site for hydrogen bond formation, theoretical calculations have been performed for a number of six-member, non-aromatic rings allowing for alternative protonation on the ring nitrogens. Gas-phase protonation studies for test molecules indicate that the B3LYP/aug-cc-pvtz and QCISD(T)CBS calculations approach the experimental values within about 1 kcal/mol with considerable improvement for relative enthalpies and free energies. Relative free energies calculated at the IEF-PCM/B3LYP/aug-cc-pvtz level predict favorable protonation on the tertiary rather than on the secondary nitrogen both in aqueous solution and in a dichloromethane solvent for saturated rings. Protonation on a nitrogen atom next to a C=C bond is disfavored due to a large increase in internal energy. Monte Carlo simulations considering a counterion and Ewald summation for the long-range electrostatic effects for a 0.1 molar model system predict ΔG(solv)/MC values generally less negative than from the IEF-PCM calculations. These results make the protonation on the tertiary nitrogen even more favored. The solute-solvent pair-energy distribution depends sensitively on the applied model. In conclusion, the freely moving anion has been considered as the most relevant model with overall neutrality for the system and applying the least restrictions.

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Section: Introductionmentioning

confidence: 99%

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Messer

2011

J. Phys. Chem. B

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“…The fraction of the latter decreases as the conformational volume of the substituent on the nitrogen atom increases [12,13]. Unsubstituted tetrahydro-1,3-oxazine was shown to exist mainly as chair conformer with axial N-H bond [11,14,15]. The results of empirical calculations demonstrated fairly strong similarity between geometric parameters, in particular dihedral angles in the carbon and heteroatom fragments in the ring, of tetrahydro-1,3-oxazine and 1,3-dioxane [16].…”

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confidence: 74%

Ab Initio conformational analysis of tetrahydro-1,3-oxazine

Кузнецов

2010

Russ J Org Chem

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Nonempirical RHF/STO-3G and 6-31G(d) studies on conformational behavior of tetrahydro-1,3-oxazine showed that interconversion between the axial (global minimum) and equatorial chair conformers can follow five independent pathways. The potential energy surface contains seven minima corresponding to chair and twist conformers, as well as seven transition states having sofa, half-chair, and symmetrical and unsymmetrical boat conformations. Additional potential barriers to interconversion, resulting from pyramidal inversion of the nitrogen atom, were also revealed.

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“…At present, however, there seems to be a satisfactory settlement in favour of the NH-equatorial form for the gas phase (Cook et al, 1973). This conclusion appears to apply equally to a variety of C-substituted piperidines in which a ring CH 2 group in position 3 or 4 has been X X…”

Section: Introductionmentioning

confidence: 83%

The crystal and molecular structure of the methanesulphonamide of morpholine (MSM): C₅H₁₁NOSO₂

Perales¹,

García-Blanco²

1977

Acta Crystallogr Sect B

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FREDERICK S. STEPHENSAND ROBERT S. VAGG 3169 structure determination show this conclusion to be incorrect and further would cast some doubt on the validity (Ablov & Samus, 1975) The structure of MSM has been determined by single-crystal X-ray diffraction techniques. The crystals are orthorhombic, space group P2~2j2~, with cell parameters a = 13.207, b = 10.078 and c = 5.7318 A; Z --4. The structure was solved with the heavy-atom method and successive Fourier syntheses. It was further refined by a least-squares technique to a final R value of 0.055 for 1051 observed reflexions, measured on an automatic four-circle diffractometer. The hetero-ring shows a chair conformation with the N-SO2-CH 3 group in the equatorial position. There are no intermolecular distances shorter than the sum of the van der Waals radii.

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The conformational analysis of saturated heterocycles. Part XLIX. The conformation of ring NH-groups in piperazines, hexahydropyrimidines, tetrahydro-1,3-oxazines, and tetrahydro-1,3-thiazines

Cited by 17 publications

References 0 publications

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Ab Initio conformational analysis of tetrahydro-1,3-oxazine

The crystal and molecular structure of the methanesulphonamide of morpholine (MSM): C₅H₁₁NOSO₂

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The conformational analysis of saturated heterocycles. Part XLIX. The conformation of ring NH-groups in piperazines, hexahydropyrimidines, tetrahydro-1,3-oxazines, and tetrahydro-1,3-thiazines

Cited by 17 publications

References 0 publications

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Ab Initio conformational analysis of tetrahydro-1,3-oxazine

The crystal and molecular structure of the methanesulphonamide of morpholine (MSM): C5H11NOSO2

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The crystal and molecular structure of the methanesulphonamide of morpholine (MSM): C₅H₁₁NOSO₂