The conformational analysis of saturated heterocycles. Part X. Steric requirements of the nitrogen lone pair from aza-cis-decalin equilibria

1967 ◽  
pp. 487 ◽  
Author(s):  
Kevan Brown ◽  
A. R. Katritzky ◽  
A. J. Waring
Keyword(s):  
Conformational Analysis ◽  
Lone Pair ◽  
Nitrogen Lone Pair ◽  
Saturated Heterocycles

A Caveat Concerning the Use of the AM1 and PM3 Semiempirical Methods in Calculating Conformational Preferences in Acyclic Amines and Saturated Azaheterocycles

1993 ◽  
Vol 46 (4) ◽  
pp. 547 ◽  
Author(s):  
MJ Shephard ◽  
MN Paddonrow
Keyword(s):  
Conformational Analysis ◽  
Lone Pair ◽  
Conformational Energy ◽  
Semiempirical Methods ◽  
Poor Agreement ◽  
Isopropyl Group ◽  
Butyl Group ◽  
Conformational Preferences ◽  
Nitrogen Lone Pair ◽  
Conformational Energies

A theoretical investigation of the conformational analysis of several acyclic amines, N- alkylated saturated azaheterocycles and alkylcyclohexanes (alkyl = Me, Et, isopropyl, t-butyl) has been carried out by using the MNDO, AM1 and PM3 semiempirical methods. It is found that all three methods correctly predict, qualitatively, the conformational preferences in alkylcyclohexanes, although the PM3 method underestimates the conformational energy for the t-butyl group by as much as 13 kJ/mol. Both AM1 and PM3 overestimate the conformational energy of the nitrogen lone pair to the extent that it exceeds that of the isopropyl group and (in the case of PM3) the t-butyl group, thereby leading to erroneous predictions of favoured conformations in amines and azaheterocycles . Thus, axial N-alkylpiperidines are predicted to be more stable than the equatorial conformers. Thus, application of the AM1 and PM3 methods to the conformational analysis of molecules containing amine functionalities is not recommended. Although the MNDO method gives a qualitative account of the conformational analysis of such molecules, with the exception of hexahydropyridazines and hexahydropyrimidines, the resulting conformational energies and molecular geometries are in poor agreement with experimental data.

ChemInform Abstract: THE CONFORMATIONAL ANALYSIS OF SATURATED HETEROCYCLES PART 56, SUBSTITUENT EFFECTS IN THE CONFORMATIONAL EQUILIBRIA OF SPIRO-OXAZOLINES

1974 ◽  
Vol 5 (20) ◽  
pp. no-no
Author(s):  
RICHARD A. Y. JONES ◽  
ALAN R. KATRITZKY ◽  
KEITH A. F. RECORD ◽  
ROGER SCATTERGOOD ◽  
JOHN M. SULLIVAN
Keyword(s):  
Conformational Analysis ◽  
Substituent Effects ◽  
Conformational Equilibria ◽  
Saturated Heterocycles

Structure and bonding in cyclic phosphoramidates as determined by carbon-13 magnetic resonance

1979 ◽  
Vol 57 (1) ◽  
pp. 21-26 ◽  
Author(s):  
Gerald W. Buchanan ◽  
Frederick G. Morin
Keyword(s):  
Magnetic Resonance ◽  
Nitrogen Atom ◽  
Electron Pair ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Ring Conformation ◽  
Delocalized Electron ◽  
Nitrogen Lone Pair ◽  
Structure And Bonding

13C chemical shifts and 13C–31P couplings are reported for 11 cyclic phosphoramidates of ring sizes from four to nine. Vicinal couplings are compared with those of carbocyclic analogs and provide insight regarding the degree of nitrogen lone pair derealization into the N—P bond. For six-membered and larger rings, there appears to be nearly complete lone pair delocalization, i.e., a trigonal planar nitrogen atom. In azetidine derivatives the nitrogen lone pair remains localized, giving rise to a highly puckered ring conformation. Pyrrolidine derivatives are viewed as having a nitrogen with a partially delocalized electron pair.

Characterization and Catalytic Activity of Poly(4-Vinylpyridine-Co-Divinylbenzene)-Co2+ Complex

2005 ◽  
Vol 494 ◽  
pp. 363-368 ◽  
Author(s):  
D. Lončarević ◽  
Ž. Čupić
Keyword(s):  
Catalytic Activity ◽  
Molecular Level ◽  
Supported Catalysts ◽  
Lone Pair ◽  
Polymer Support ◽  
Polymeric Complex ◽  
Reaction Conditions ◽  
Pyridine Nitrogen ◽  
Nitrogen Lone Pair ◽  
Thermal Stability Of

Poly(4-vinylpyridine-co-divinylbenzene)-Co2+ was characterized using infrared spectroscopy (IR), thermogravimetric analysis (TG-DTA), N2-physisorption and polarography. Thermal analysis suggests sufficient thermal stability of the polymer support, under reaction conditions. From polarography measurements, the Co2+ content on polymer-supported catalysts is estimated and it was proved that no significant leaching occurred during the activity tests. At the molecular level, FTIR of P4VP-DVB-Co2+ reveals that the pyridine nitrogen lone pair coordinates to the metal center in the polymeric complex. The obtained P4VP-DVB-Co2+ catalysts performed interesting catalytic activity in reaction of the cyclohexane oxidation with air, indicating that increasing Co2+ content lowers the initiation temperature and raises the decomposition of cyclohexylhydroperoxide.

scholarly journals The N-atom in [N(PR3)2]+ cations (R = Ph, Me) can act as electron donor for (pseudo) anti-electrostatic interactions

CrystEngComm ◽  
2015 ◽  
Vol 17 (20) ◽  
pp. 3768-3771 ◽  
Author(s):  
Antonio Bauzá ◽  
Antonio Frontera ◽  
Tiddo J. Mooibroek ◽  
Jan Reedijk
Keyword(s):  
Hydrogen Bonding ◽  
Electron Donor ◽  
Molecular Hydrogen ◽  
Electrostatic Interactions ◽  
Lone Pair ◽  
Dft Study ◽  
Nitrogen Lone Pair

A CSD analysis and DFT study reveal that the nitrogen lone-pair in [N(PPh3)2]+ is partially intact and involved in intramolecular hydrogen bonding.

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