Search results for "bonds"
showing 10 items of 155 documents
Crystal structure of hydrocortisone 17-butyrate
2014
In the title compound, C25H36O6, the two central cyclohexane rings exhibit a chair conformation. The terminal cyclohexene and cyclopentane rings are in half-chair and envelope conformations (with the C atom bearing the methyl substituent as the flap), respectively. The methyl group of the butyrate chain is disordered over two orientations, with a refined occupancy ratio of 0.742 (6):0.258 (6). Intramolecular O—H...O and C—H...O hydrogen bonds are observed. In the crystal, molecules are linked by O—H...O hydrogen bonds into chains running parallel to theaaxis.
Substituent Effects on the [N−I−N]+ Halogen Bond
2016
We have investigated the influence of electron density on the three-center [N–I–N]+ halogen bond. A series of [bis(pyridine)iodine]+ and [1,2-bis((pyridine-2-ylethynyl)benzene)iodine]+ BF4– complexes substituted with electron withdrawing and donating functionalities in the para-position of their pyridine nitrogen were synthesized and studied by spectroscopic and computational methods. The systematic change of electron density of the pyridine nitrogens upon alteration of the para-substituent (NO2, CF3, H, F, Me, OMe, NMe2) was confirmed by 15N NMR and by computation of the natural atomic population and the π electron population of the nitrogen atoms. Formation of the [N–I–N]+ halogen bond re…
IR Bandshapes of Intramolecularly H-Bonded Systems II. 2,4-Dibromophenol
1984
A detailed quantitative study of the IR bandshape of the ϑs(OH) vibration of 2,4-dibromophenol in a series of solvents is presented.A distinct dependence of band positions, shape parameters, correlation functions and correlation times from solvent polarity has been found.The contribution of various shaping mechanisms to the profile is discussed.
FTIR matrix isolation and theoretical studies of glycolic acid dimers
2018
Glycolic acid (GA) dimers were studied in low temperature argon matrices by means of FTIR spectroscopy. Experimentally, the dimers were produced when monomeric glycolic acid molecules were thermally mobilized upon annealing of argon matrices at 25–35 K. The experimental spectra observed upon annealing indicate the presence of three different dimer structures. Computationally, MP2 and DFT calculations were used to study the potential dimer species in order to scrutinize the possible dimer structures, their energetics and their spectral features. Altogether 27 local minima were found for dimer structures for the three lowest conformers of glycolic acid considered based on previous studies on …
Halogen bonds in 2,5-dihalopyridine-copper(II) chloride complexes
2018
Ten coordination complexes obtained through a facile reaction between 2,5-dihalopyridines and copperIJII) chloride (CuCl2) are characterized using single crystal X-ray diffraction. Two series of dihalopyridine complexes based on 2-chloro-5-X-pyridine and 2-bromo-5-X-pyridine (X = F, Cl, Br and I) were prepared to analyze the C–X2/X5⋯Cl–Cu halogen bonds (XB). The influence of X2- and X5-substituents on the respective interactions was examined by comparing them to the X2/X3⋯Cl–Cu XBs found in mono-substituted halopyridine complexes, (n-X-pyridine)2·CuCl2 (n = 2, 3 and X = Cl, Br and I). Varying the X5-halogens in (2,5-dihalopyridine)2·CuCl2, the C5–X5⋯Cl–Cu XBs follow the order F5 1 and they c…
Tridentate C–I⋯O−–N+ halogen bonds
2017
The X-ray structures of the first co-crystals where the three oxygen lone pairs in N-oxides are fully utilized for tridentate C–I⋯O−–N+ halogen bonding with 1,ω-diiodoperfluoroalkanes are reported, studied computationally, and compared with the corresponding silver(I) N-oxide complexes. peerReviewed
A Novel Halogen Bond Acceptor : 1-(4-Pyridyl)-4-Thiopyridine (PTP) Zwitterion
2020
Sulfur is a widely used halogen bond (XB) acceptor, but only a limited number of neutral XB acceptors with bifurcated sp3-S sites have been reported. In this work a new bidentate XB acceptor, 1-(4-pyridyl)-4-thiopyridine (PTP), which combines sp3-S and sp2-N acceptor sites, is introduced. Three halogen bonded cocrystals were obtained by using 1,4-diiodobenzene (DIB), 1,4-diiodotetrafluorobenzene (DIFB), and iodopentafluorobenzene (IPFB) as XB donors and PTP as acceptor. The structures of the cocrystals showed some XB selectivity between the S and N donors in PTP. However, the limited contribution of XB to the overall molecular packing in these three cocrystals and the results from DSC measu…
Strong N−X···O−N Halogen Bonds: Comprehensive Study on N‐Halosaccharin Pyridine N‐oxide Complexes
2019
A detailed study of the strong N−X⋯−O−N+ (X = I, Br) halogen bonding interactions in solution and in the solid‐state reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). Density Functional Theory (DFT) calculations were used to investigate the X···O halogen bond (XB) interaction energies in 54 complexes. The XB interaction energies were found to vary from –47.5 to –120.3 kJ mol–1, with the strongest N−I⋯−O−N+ XBs approaching those of 3‐center‐4‐electron [N–I–N]+ halogen‐bonded systems (∼160 kJ mol–1). Using a subset of 32 complexes, stabilized only through N−X···−O−N+ XB interactions, a simplified, computationally fast, electrostatic model to predict the X…
Self-Complementary Dimers of Oxalamide-Functionalized Resorcinarene Tetrabenzoxazines
2018
Self‐complementarity is a useful concept in supramolecular chemistry, molecular biology and polymeric systems. Two resorcinarene tetrabenzoxazines decorated with four oxalamide groups were synthesized and characterized. The oxalamide groups possessed self‐complementary hydrogen bonding sites between the carbonyls and amide groups. The self‐complementary nature of the oxalamide groups resulted in self‐included dimeric assemblies. The hydrogen bonding interactions within the tetrabenzoxazines gave rise to the formation of dimers, which were confirmed by single‐crystal X‐ray diffractions analysis and supported by NMR spectroscopy and mass spectrometry. The self‐included dimers were connected b…
Simple Rules for Complex Near-Glass-Transition Phenomena in Medium-Sized Schiff Bases
2022
Glass-forming ability is one of the most desired properties of organic compounds dedicated to optoelectronic applications. Therefore, finding general structure–property relationships and other rules governing vitrification and related near-glass-transition phenomena is a burning issue for numerous compound families, such as Schiff bases. Hence, we employ differential scanning calorimetry, broadband dielectric spectroscopy, X-ray diffraction and quantum density functional theory calculations to investigate near-glass-transition phenomena, as well as ambient- and high-pressure molecular dynamics for two structurally related Schiff bases belonging to the family of glycine imino esters. Firstly…