Switching between ring closed and open N-incorporated heterocycles with tuneable charges and modular reactivity based upon 5-(2-bromoethyl)phenanthridinium bromide

5-(2-bromoethyl)phenanthridinium bromide (BEP) undergoes a 3-step-one-pot cyclisation reaction with primary amines allowing the facile synthesis of a vast library of heterocycles. A diverse range of primary aryl amines were explored as reactants to gain insight into the product isolated as a result of the steric and electronic effects of the aryl precursors. Analysis and reaction monitoring with UV-vis and NMR spectroscopy revealed that excessively electron withdrawing groups and sterically hindered amines do not allow for isolation of the common neutral tetrahydroimidazophenanthridine (TIP) structure but allow either the isolation of the charged dihydroimadazophenanthridinium (DIP) or aminoethylphenanthridinium (AEP) products.     

Direct methoxypyridine functionalization approach to magellanine-type Lycopodium alkaloids

A concise enantioselective approach to the tetracyclic core of the magellanine-type Lycopodium alkaloids is reported. Key to this approach is the use of the Hajos-Parrish reaction to set a challenging quaternary stereocenter, thereby guiding the stereoselectivity for the remainder of the synthesis, as well as the use of a palladium-mediated direct pyridine functionalization reaction to forge the tetracyclic core.     

Theoretical Studies on the Binding of Cd~（2＋） to Uracil and Its Thio-derivatives

The interaction of Cd2+ with uracil,2-thiouracil,4-thiouracil and 2,4-dithiouracil have been investigated by the density functional theory(DFT) calculations.For uracil and 2,4-dithiouracil,where the two basic sites are the same,Cd2+ attachment to the heteroatom at position 4 is preferred.However,for the systems where both types of basic centers,a carbonyl and a thiocarbonyl groups,are present,Cd2+ association with sulfur is favorable.The enhanced stability of these enolic and thiol forms comes from Cd2+ interaction with two basic sites simultaneously,which thereby triggers a significant aromatization of the ring.More significantly,the Cd2+ binding energy with uracil and its thio-derivatives is larger than the tautomerization barriers connecting the diketo-like forms with the corresponding enolic-like tautomers.Consequently,when associated with Cd2+,all tautomers are energetically accessible and should be observed in the gas phase.     

Uptake of SO2 to aqueous formaldehyde surfaces

Aqueous surfaces act as a gateway to absorption and aqueous-phase reaction of gases in the atmosphere. The composition of aerosols varies greatly and is expected to influence the structure of the interface. For example, aldehydes comprise a significant fraction of atmospheric organics and are likely to accumulate at aqueous surfaces. But it is difficult to anticipate their effect on the migration of gaseous species through the interfacial region. Surface organics may act as a barrier to absorption, or they may facilitate uptake via cooperative interactions with absorbing compounds. The surface spectroscopic studies presented here examine the nature of the vapor/water interface during uptake of SO(2) to aqueous formaldehyde solutions, elucidating the role of surface species in a multicomponent interfacial system. The results show that the product of the reaction between SO(2) and formaldehyde, hydroxymethanesulfonate, shows a surface affinity that is enhanced in the presence of SO(2).     

Molecular modeling of phosphonate molecules onto barium sulfate terraced surfaces

The adsorption of phosphonate molecules onto mineral surfaces is of interest due to their use as scale inhibitors. Molecular modeling is an important tool that can aid the fundamental understanding of how these inhibitors operate. This paper presents an empirical molecular mechanics study of the adsorption of a series of straight chain phosphonate molecules onto barium sulfate. It has been found that inhibition can be predicted for this straight chain series of molecules, which differ by the number of phosphonate groups present as well as by the chain length. Even more importantly, the modeling results can predict which faces will be preferred, and this has been verified by scanning and transmission electron microscopy on the resultant barite particles. It has been found that, in general, lattice matching results in the lowest replacement energy for all of the organic molecules investigated. The agreement between the experiment and the model confirms that the dominant mechanism of interaction for the additives on barium sulfate is via the deprotonated phosphonate groups with the barium ions on the surface.     

Spectroscopic studies of solvated hydrogen and hydroxide ions at aqueous surfaces

Measuring the molecular properties of the surface of acidic and basic aqueous solutions is essential to understanding a wide range of important biological, chemical, and environmental processes on our planet. In the present studies, vibrational sum-frequency spectroscopy (VSFS) is employed in combination with isotopic dilution experiments at the vapor/water interface to elucidate the interfacial water structure as the pH is varied with HCl and NaOH. In acidic solutions, solvated proton species are seen throughout the interfacial region, and they alter the hydrogen bonding between water molecules in ways that reflect their depth in the interfacial region. At the higher frequencies of the OH stretch region, there is spectral evidence for solvated proton species residing in the topmost layers of the interfacial region. As reported in previous VSF studies, more strongly bound solvated proton species are observed at lower OH stretching frequencies. The solvated proton species that have stronger hydrogen bonding are similar in structure to those found in bulk acid solutions and likely reside somewhat deeper in the interfacial region. There is also evidence of OH stretching from solvated protons and relatively strong hydrogen bonding in the solvation sphere that is similar to other solvated ions. In contrast, water molecules solvating OH(-) ions show relatively weak hydrogen bonding and significantly less interfacial order. VSF spectra are acquired under multiple polarizations to provide crucial information for the interpretation of the spectra and for the determination of interfacial structure.     

Synthesis of a Chiral Quaternary Carbon Center Bearing a Fluorine Atom: Enantio‐ and Diastereoselective Guanidine‐Catalyzed Addition of Fluorocarbon Nucleophiles

The perfect combination : The title reaction provides adducts having quaternary carbon centers bearing a fluorine atom with high ee and d.r. values (see scheme). The mechanism and origin of stereoselectivity were elucidated by DFT calculations. The bifunctional mode of the guanidine catalysis was demonstrated in the transition states resulting from the DFT results.

     

Chloride Metathesis and Dimethylamide Transfer in the Reaction of TaCl(NMe2)4 with ZnMe2 and MeMgCl: Spectroscopic Studies and X-ray Diffraction Structures of TaCl(Me)(NMe2)3 and ZnCl2(NHMe2)2

Abstract  

Treatment of TaCl(NMe₂)₄ with ZnMe₂ in pentane furnishes a mixture of TaCl(Me)(NMe₂)₃, TaMe(NMe₂)₄, and Ta(NMe₂)₅ as the principal reaction products based on ¹H NMR spectroscopy. Depending upon the work-up conditions employed, the compounds TaCl(Me)(NMe₂)₃ and ZnCl₂(NHMe₂)₂ have been isolated and their molecular structures established by X-ray crystallography. TaCl(Me)(NMe₂)₃ crystallizes in the orthorhombic space group Pna2₁, a = 13.644(4) ?, b = 12.934(4) ?, c = 6.992(2) ?, V = 1233.9(7) ?³, Z = 4, and d _calc = 1.958 Mg/m³; R = 0.0316 and wR ₂ = 0.0707 for 2630 reflections with I > 2σ(I). The molecular structure of TaCl(Me)(NMe₂)₃ consists of a trigonal bipyramidal core and contains axial and equatorial chlorine and methyl groups, respectively. ZnCl₂(NHMe₂)₂ crystallizes in the orthorhombic space group P2₁2₁2₁, a = 5.759(1) ?, b = 10.810(2) ?, c = 15.174(3) ?, V = 944.1(3) ?³, Z = 4, d _calc = 1.593 Mg/m³; R = 0.0213 and wR ₂ = 0.0494 for 1872 reflections with I > 2σ(I). ZnCl₂(NHMe₂)₂ exhibits a tetrahedral motif and represents the first reported four-coordinate zinc(II) compound containing acyclic monodentate secondary amine groups. The reaction between TaCl(NMe₂)₄ and MeMgCl afforded a mixture of tantalum products, of which TaCl(Me)(NMe₂)₃ and Ta(NMe₂)₅ were found as the major products by ¹H NMR spectroscopy.