Despite the romantic mythology that often accompanies stories of scientific discovery, pinpointing the exact moment in history when a new concept emerged is often a matter of debate — and the ...hydrogen bond is no exception explains Bruce C. Gibb.
The synthesis, isolation and full characterisation of a Cu(IPr)(OC(H)(CF
)
) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) complex are reported. This new Cu(I) complex is a versatile ...synthon and can activate numerous X-H bonds including C-H, N-H and S-H bonds. Cu(IPr)(OC(H)(CF
)
) was investigated as a pre-catalyst in several catalytic reactions.
Unsaturated
N
2
-sulfonyl amidines are transformed into valuable N-heterocyclic products when heated with BF
2
OTf. Mechanism studies suggest a domino 1,7-H shift, activating a C-H bond, followed by ...electrocylisation that results in stereodefined cyclic amidines.
Heating unsaturated
N
2
-sulfonyl amidines with BF
2
OTf in acetonitrile transformed them into stereodefined cyclic amidines. Investigating by-products of the reaction suggested a fascinating mechanism including 1,7-H shift and electrocyclisation.
Presented herein is the synthesis of diversely functionalized pyrrolizines from the reaction of
N
-alkoxycarbamoyl pyrroles with CF
3
-ynones. The formation of the product is based on a C-H bond ...activation-initiated cascade process including
N
-alkoxycarbamoyl group-directed alkenylation of the pyrrole scaffold followed by simultaneous intramolecular nucleophilic addition along with cleavage and transfer of the directing group. By taking advantage of the rich chemistry of the transferred alkoxycarbamoyl moiety, the products could be transformed into a series of structurally and biologically interesting pyrrolizine derivatives. To our knowledge, this is the first example in which the
N
-alkoxycarbamoyl unit acted as a transferable and transformable directing group for the divergent synthesis of pyrrolizines.
Presented herein is the synthesis of diversely functionalized pyrrolizines from the reaction of
N
-alkoxycarbamoyl pyrroles with CF
3
-ynones.
Imidazole is a five‐membered heterocycle that is part of a number of biologically important molecules such as the amino acid histidine and the hormone histamine. Imidazole has a unique ability to ...participate in a variety of non‐covalent interactions involving the NH group, the pyridine‐like nitrogen atom or the π‐system. For many biologically active compounds containing the imidazole moiety, its participation in formation of hydrogen bond NH⋯O/N and following proton transfer is the key step of mechanism of their action. In this work a systematic study of the mutual influence of various paired combinations of non‐covalent interactions (e.g., hydrogen bonds and π‐interactions) involving the imidazole moiety was performed by means of quantum chemistry (PW6B95‐GD3/def2‐QZVPD) for a series of model systems constructed based on analysis of available x‐ray data. It is shown that for considered complexes formation of additional non‐covalent interactions can only enhance the proton‐donating ability of imidazole. At the same time, its proton‐accepting ability can be both enhanced and weakened, depending on what additional interactions are added to a given system. The mutual influence of non‐covalent interactions involving imidazole can be classified as weak geometric and strong energetic cooperativity—a small change in the length of non‐covalent interaction formed by imidazole can strongly influence its strength. The latter can be used to develop methods for controlling the rate and selectivity of chemical reactions involving the imidazole fragment in larger systems. It is shown that the strong mutual influence of non‐covalent interactions involving imidazole is due to the unique ability of the imidazole ring to effectively redistribute electron density in non‐covalently bound systems with its participation.
The possibilities of tuning the strength of hydrogen bonds involving the imidazole ring through the formation of additional non‐covalent interactions have been systematically studied.
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•The facile and controllable synthesis for monoclinic WO3 nanospheres.•The novel three-dimensional equilibrium diffusion behaviors for monoclinic WO3.•The continuous geometric ...evolutions of hydrogen bonds for monoclinic WO3.•WO3 revealed fast kinetics and durable stability for aqueous ammonium-ion batteries.
Aqueous ammonium-ion batteries (AAIBs) have attracted tremendous attentions due to their plentiful resources, inherent security and environmental friendliness. From the first-principles calculations and ex-situ measurements, monoclinic WO3 revealed the three-dimensional equilibrium diffusion behaviors during the electrochemical processes, and the novel evolution processes of reversible building/breaking between geometric hydrogen bonds and traditional linear hydrogen bonds. Specifically, monoclinic WO3 delivered a high specific capacity of 150.6 mAh g-1 at the current density of 0.1 A g-1, and exhibited excellent rate capability of 48 mAh g-1 at the current density of 5.0 A g-1 and outstanding cycling stability of 86.6 % capacity retention after 500 cycles. Furthermore, the ammonium-ion full batteries based on the monoclinic WO3 anode and γ-MnO2 cathode achieved a perfect energy density of 64.9 Wh kg-1 and an extreme ultra-long lifespan with 95.4 % capacity retention after 5000 cycles at the current density of 3.0 A g-1. Thus, the novel insights on NH4+ diffusion behaviors and the evolution mechanisms of hydrogen bonds could promote the development of the practical applications for monoclinic WO3 in aqueous ammonium-ion batteries.
DFT and TD-DFT were used in this article to investigate the effects of different substitutions at multiple sites on the photophysical mechanism of bis-HBX in the gas phase. Four different ...substitution modes were selected, denoted as A1 (X=Me, Y=S), A2 (X=OMe, Y=S), B1 (X=Me, Y=NH), and C1 (X=Me, Y=O). The geometric parameters proved that the IHBs enhanced after photoexcitation, which was conducive to promote the ESIPT process. Combining the analysis of the PECs, it was revealed that the bis-HBX molecule underwent the ESIPT process, and the ease of the ESIPT process was in the order of A1 > A2> B1 > C1. In particular, the TICT process in A1 and B1 promoted the occurrence of the ESIPT process. In addition, the IC process was identified, particularly in C1. Meanwhile, the calculation of fluorescence lifetime and fluorescence rate further confirmed that A1 was the most effective fluorescent probe molecule. This theoretical research provides an innovative theoretical reference for regulating ESIPT reactions and optimizing fluorescent probe molecules.
Carbonyl–carbonyl (CO⋯CO) n → π* interaction often coexists with a hydrogen bond (HB) or another n → π* interaction. Although the interplay between HB and n → π* interaction was previously studied, ...there is no systematic investigation that shows a synergistic relationship of n → π* with another noncovalent interaction. Herein, we have studied a set of proline-diacylhydrazine (Pro-DAH) molecules and observed that increase in the strength of the nN → π*Ar interaction on their DAH side strengthened the n → π* interaction on the Pro side, which was experimentally determined by measuring the Ktrans/cis of the Xaa–Pro amide bond. Overall, we describe a simple C-terminal modification strategy to stabilize the trans-Pro geometry that could be useful to stabilize PPII helices and collagen triple helices that require Pro to adopt the trans amide geometry.
The Cover Feature shows the uncommon hydrogen bond donor property of ammonia investigated by forming 1:1 complexes under cold conditions of matrix isolation, which are probed using infrared ...spectroscopy. The hydrogen bond complexes are formed between ammonia and three acceptor molecules containing chalcogen atoms (O, S, and Se) at the active site. Cover design by Dhritabrata Pal and Shamik Chakraborty. More information can be found in the Research Article by Dhritabrata Pal and Shamik Chakraborty.
In this work the first examples of C–N bond activation by insertion into a geometrically constrained PIII-centre are shown. The mechanisms of these activation processes leading to new PV species were ...studied both experimentally and computationally. Interestingly, in the case of insertion of the PIII-centre into an N–C(O)H bond, an unstable phosphoranyl-formaldehyde intermediate is probably formed, which undergoes decarbonylation in the presence of a catalytic amount of HCl producing a hydrophosphorane.
![An air-stable [Cu(NHC)(OR)]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1359-7345/small "An air-stable [Cu(NHC)(OR)] (R = C(H)(CF 3 ) 2 ) complex for C-H, N-H and S-H bond activation")
