A theoretical conformational analysis of morpholine

Capparelli, Alberto L.; Marañon, Julio; Sorarrain, O. M.; Filgueria, Roberto R.

doi:10.1016/0022-2860(74)85064-7

Cited by 18 publications

(4 citation statements)

References 9 publications

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“…These molecules differ from each other in the conformation of the N -alkyl morpholine moiety, which adopts equatorial (Molecule a ) and axial (Molecule b ) conformations, respectively. We remind the reader that equatorial/axial conformations are separated by ∼1 kcal·mol –1 in a morpholine molecule itself . In general, the X-ray structures of Ir1 and Ir2 are similar, but differ in the conformation of either the six-membered (IrNCCCN) iridacycle ring or morpholine auxiliary, the latter of which adopts an equatorial and/or axial conformation.…”

Section: Resultsmentioning

confidence: 95%

Why Does Alkylation of the N–H Functionality within M/NH Bifunctional Noyori-Type Catalysts Lead to Turnover?

2017

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Molecular metal/NH bifunctional Noyori-type catalysts are remarkable in that they are among the most efficient artificial catalysts developed to date for the hydrogenation of carbonyl functionalities (loadings up to ∼10 mol %). In addition, these catalysts typically exhibit high C═O/C═C chemo- and enantioselectivities. This unique set of properties is traditionally associated with the operation of an unconventional mechanism for homogeneous catalysts in which the chelating ligand plays a key role in facilitating the catalytic reaction and enabling the aforementioned selectivities by delivering/accepting a proton (H) via its N-H bond cleavage/formation. A recently revised mechanism of the Noyori hydrogenation reaction (Dub, P. A. et al. J. Am. Chem. Soc. 2014, 136, 3505) suggests that the N-H bond is not cleaved but serves to stabilize the turnover-determining transition states (TDTSs) via strong N-H···O hydrogen-bonding interactions (HBIs). The present paper shows that this is consistent with the largely ignored experimental fact that alkylation of the N-H functionality within M/NH bifunctional Noyori-type catalysts leads to detrimental catalytic activity. The purpose of this work is to demonstrate that decreasing the strength of this HBI, ultimately to the limit of its complete absence, are conditions under which the same alkylation may lead to beneficial catalytic activity.

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Section: Resultsmentioning

confidence: 95%

Why Does Alkylation of the N–H Functionality within M/NH Bifunctional Noyori-Type Catalysts Lead to Turnover?

2017

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“…20,21 Evidence for two conformeric forms was supported by early ab initio studies, which predicted the EQ conformer to be the lower energy form and enabled assignment of the room temperature IR spectrum. 22 These studies also identified the boat conformer, lying $3000 cm À1 higher in energy, which made no contribution to the IR spectrum. However, microwave studies only revealed evidence for the EQ chair conformer.…”

Section: Introductionmentioning

confidence: 95%

The conformer resolved ultraviolet photodissociation of morpholine

2010

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“…It can exist in chair or skew boat conformers. It is a well established fact that the boat conformations are higher in energy compared to the chair conformations, and hence, they have no contribution in the IR or microwave spectra of morpholine. , Therefore, this conformation has been considered negligible for bulk studies until now in literature. There can be multiple chair conformations, due to different orientations of the N–H bond with respect to the plane of the ring.…”

Section: Resultsmentioning

confidence: 99%

Vibrational Sum-Frequency Generation Study of Morpholine at Air–Liquid and Air–Solution Interfaces

et al. 2016

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The structure and orientation of interfacial morpholine molecules have been investigated, using vibrational sum-frequency generation (VSFG) spectroscopya nonlinear surface specific technique. The VSFG spectra with SSP and PPP polarizations have been measured in the CH (2800–3000 cm–1) and the OH (3000–3750 cm–1) stretch regions at the air–morpholine and air–solution interfaces. The vibrational frequencies in the CH stretch region could be observed in VSFG spectra, implying presence of morpholine molecules at the interfaces with net polar orientation. The intensities of the CH stretch bands get enhanced at the air–solution interface of morpholine solution in millimolar concentration, in comparison to that at the air–morpholine interface which is attributed to increase in polar orientation of interfacial morpholine molecules induced by water molecules. In pure morpholine, the most predominant conformation of molecules is equatorial chair, both in the bulk and at the air–morpholine interface. But in aqueous solution of morpholine, the contribution from axial chair conformer is known to increase. This effect, and also a probable change from the chair to the boat/twist boat conformation at the air–solution interface, may contribute to the enhanced intensity of VSFG peaks of CH stretch bands in solution. The VSFG intensities of the OH stretching frequencies of interfacial water molecules are also enhanced in the presence of morpholine, suggesting an increase in net polar orientation of water molecules induced by morpholine molecules. The VSFG spectra were also measured in the presence of 300 mM HCl, which showed indications of protonation of the interfacial morpholine molecules. Addition of HCl to aqueous solution of morpholine alters the orientation of interfacial water molecules significantly, and the enhanced VSFG intensities in the OH region induced by morpholine molecules are almost completely obliterated. The result suggests that orientation of interfacial water molecules in the presence of HCl gets random. However, the effects of HCl in the CH region of the VSFG spectra differ for different stretching bands. In presence of readily ionizable HCl molecules, a large number of ions are generated, which are probably responsible for changing the surface orientation of both water and morpholine molecules.

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A theoretical conformational analysis of morpholine

Cited by 18 publications

References 9 publications

Why Does Alkylation of the N–H Functionality within M/NH Bifunctional Noyori-Type Catalysts Lead to Turnover?

Why Does Alkylation of the N–H Functionality within M/NH Bifunctional Noyori-Type Catalysts Lead to Turnover?

The conformer resolved ultraviolet photodissociation of morpholine

Vibrational Sum-Frequency Generation Study of Morpholine at Air–Liquid and Air–Solution Interfaces

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