- High-Field NMR Spectroscopy Reveals Aromaticity-Modulated Hydrogen Bonding in Heterocycles
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From DNA base pairs to drug–receptor binding, hydrogen (H-)bonding and aromaticity are common features of heterocycles. Herein, the interplay of these bonding aspects is explored. H-bond strength modulation due to enhancement or disruption of aromaticity of heterocycles is experimentally revealed by comparing homodimer H-bond energies of aromatic heterocycles with analogs that have the same H-bonding moieties but lack cyclic π-conjugation. NMR studies of dimerization in C6D6 find aromaticity-modulated H-bonding (AMHB) energy effects of approximately ±30 %, depending on whether they enhance or weaken aromatic delocalization. The attendant ring current perturbations expected from such modulation are confirmed by chemical shift changes in both observed ring C?H and calculated nucleus-independent sites. In silico modeling confirms that AMHB effects outweigh those of hybridization or dipole–dipole interaction.
- Kakeshpour, Tayeb,Bailey, John P.,Jenner, Madison R.,Howell, Darya E.,Staples, Richard J.,Holmes, Daniel,Wu, Judy I.,Jackson, James E.
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supporting information
p. 9842 - 9846
(2017/08/08)
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- METHODS FOR THE SYNTHESIS OF POLYCYCLIC GUANIDINE COMPOUNDS
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The present invention provides methods for the synthesis of polycyclic guanidine compounds. In certain embodiments, provided methods include the step of contacting a described reagent with a triamine compound to provide a polycyclic guanidine compound.
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Page/Page column 25
(2011/07/09)
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- Ti-amide catalyzed synthesis of cyclic guanidines from di-/triamines and carbodiimides
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A titanacarborane monoamide catalyzed, one-step synthesis of mono/bicyclic guanidines from commercially available di/triamines and carbodiimides is reported. The reaction mechanism is also proposed.
- Shen, Hao,Wang, Yang,Xie, Zuowei
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supporting information; experimental part
p. 4562 - 4565
(2011/10/12)
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- Catalytic Depolymerization of Polymers Containing Electrophilic Linkages Using Nucleophilic Reagents
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The disclosure relates to methods and materials useful for depolymerizing a polymer. In one embodiment, for example, the disclosure provides a method for depolymerizing a polymer containing electrophilic linkages, wherein the method comprises contacting t
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Page/Page column 10
(2011/01/12)
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- Cyclic guanidine organic catalysts: What is magic about triazabicyclodecene?
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(Chemical Equation Presented) The bicyclic guanidine 1,5,7- triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for the formation of amides from esters and primary amines. Mechanistic and kinetic investigations support a nucleophilic mechanism where TBD reacts reversibly with esters to generate an acyl-TBD intermediate that acylates amines to generate the amides. Comparative investigations of the analogous bicyclic guanidine 1,4,6-triazabicyclo[3.3.0]oct-4-ene (TBO) reveal it to be a much less active acylation catalyst than TBD. Theoretical and mechanistic studies imply that the higher reactivity of TBD is a consequence of both its higher basicity and nucleophilicity than TBO as well as the high reactivity of the acyl-TBD intermediate, which is sterically prevented from adopting a planar amide structure.
- Kiesewetter, Matthew K.,Scholten, Marc D.,Kirn, Nicole,Weber, Ryan L.,Hedrick, James L.,Waymouth, Robert M.
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experimental part
p. 9490 - 9496
(2010/03/24)
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