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Hydrogen-bond Acceptors (hydrogen-bond + acceptor)
Selected AbstractsMain-chain, thermotropic, liquid-crystalline, hydrogen-bonded polymers of 4,4,-bipyridyl with aliphatic dicarboxylic acidsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2003Pradip K. Bhowmik Abstract A series of main-chain, thermotropic, liquid-crystalline (LC), hydrogen-bonded polymers or self-assembled structures based on 4,4,-bipyridyl as a hydrogen-bond acceptor and aliphatic dicarboxylic acids, such as adipic and sebacic acids, as hydrogen-bond donors were prepared by a slow evaporation technique from a pyridine solution and were characterized for their thermotropic, LC properties with a number of experimental techniques. The homopolymer of 4,4,-bipyridyl with adipic acid exhibited high-order and low-order smectic phases, and that with sebacic acid exhibited only a high-order smectic phase. Like the homopolymer with adipic acid, the two copolymers of 4,4,-bipyridyl with adipic and sebacic acids (75/25 and 25/75) also exhibited two types of smectic phases. In contrast, the copolymer of 4,4,-bipyridyl with adipic and sebacic acids (50/50), like the homopolymer with sebacic acid, exhibited only one high-order smectic phase. Each of them, including the copolymers, had a broad temperature range of LC phases (36,51 °C). The effect of copolymerization for these hydrogen-bonded polymers on the thermotropic properties was examined. Generally, copolymerization increased the temperature range of LC phases for these polymers, as expected, with a larger decrease in the crystal-to-LC transition than in the LC-to-isotropic transition. Additionally, it neither suppressed the formation of smectic phases nor promoted the formation of a nematic phase in these hydrogen-bonded polymers, as usually observed in many thermotropic LC polymers. The thermal transitions for all of them, measured by differential scanning calorimetry, were well below their decomposition temperatures, as measured by thermogravimetric analysis, which were in the temperature range of 193,210 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1282,1295, 2003 [source] Amino and cyano N atoms in competitive situations: which is the best hydrogen-bond acceptor?ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2001A crystallographic database investigation The relative hydrogen-bond acceptor abilities of amino and cyano N atoms have been investigated using data retrieved from the Cambridge Structural Database and via ab initio molecular orbital calculations. Surveys of the CSD for hydrogen bonds between HX (X = N, O) donors, N,T,C,N (push,pull nitriles) and N,(Csp3)n,C,N molecular fragments show that the hydrogen bonds are more abundant on the nitrile than on the amino nitrogen. In the push,pull family, in which T is a transmitter of resonance effects, the hydrogen-bonding ability of the cyano nitrogen is increased by conjugative interactions between the lone pair of the amino substituent and the C,N group: a clear example of resonance-assisted hydrogen bonding. The strength of the hydrogen-bonds on the cyano nitrogen in this family follows the experimental order of hydrogen-bond basicity, as observed in solution through the pKHB scale. The number of hydrogen bonds established on the amino nitrogen is greater for aliphatic aminonitriles N,(Csp3)n,C,N, but remains low. This behaviour reflects the greater sensitivity of the amino nitrogen to steric hindrance and the electron-withdrawing inductive effect compared with the cyano nitrogen. Ab initio molecular orbital calculations (B3LYP/6-31+G** level) of electrostatic potentials on the molecular surface around each nitrogen confirm the experimental observations. [source] Different hydrogen-bonding modes in two closely related oximesACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010Grzegorz Dutkiewicz Two closely related oximes, namely 1-chloroacetyl-3-ethyl-2,6-diphenylpiperidin-4-one oxime, C21H23ClN2O2, (I), and 1-chloroacetyl-2,6-diphenyl-3-(propan-2-yl)piperidin-4-one oxime, C22H25ClN2O2, (II), despite their identical sets of hydrogen-bond donors and acceptors, display basically different hydrogen-bonding patterns in their crystal structures. While the molecules of (I) are organized into typical centrosymmetric dimers, created by oxime,oxime O,H...N hydrogen bonds, in the structure of (II) there are infinite chains of molecules connected by O,H...O hydrogen bonds, in which the carbonyl O atom from the chloroacetyl group acts as the hydrogen-bond acceptor. Despite the differences in the hydrogen-bond schemes, the ,OH groups are always in typical anti positions (C,N,O,H torsion angles of ca 180°). The oxime group in (I) is disordered, with the hydroxy groups occupying two distinct positions and C,C,N,O torsion angles of approximately 0 and 180° for the two alternatives. This disorder, even though the site-occupancy factor of the less occupied position is as low as ca 0.06, is also observed at lower temperatures, which seems to favour the statistical and not the dynamic nature of this phenomenon. [source] Tris(1,10-phenanthroline-,2N,N,)cadmium(II) bis(perchlorate) 3.5-hydrate: a water chain stabilized by perchlorate anionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Yu-Hui Sun The title compound, [Cd(C12H8N2)3](ClO4)2·3.5H2O, contains a cross-shaped one-dimensional channel along the c axis which encapsulates an ordered water chain. This water chain features a centrosymmetric cyclic water hexamer unit with a chair-like conformation. Neighbouring hexamers are linked by bridging water molecules. The host perchlorate anions recognize and stabilize the guest water chain via three kinds of hydrogen-bond patterns, leading to the formation of a complex one-dimensional {[(H2O)7(ClO4)4]4,}n anionic chain. One perchlorate acts as a single hydrogen-bond acceptor dangling on the chain, the second perchlorate on the chain serves as a double hydrogen-bond acceptor for only one water molecule to form an R22(6) ring, where both entities lie on a twofold axis, while the third perchlorate, which also lies on a twofold axis, accepts two hydrogen bonds from two equivalent water molecules and is involved in the construction of an R65(14) ring. [source] A novel three-dimensional framework constructed by 2-[(1H -imidazol-1-yl)methyl]-1H -benzimidazole and infinite chains of hydrogen-bonded water moleculesACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009De-Qiang Qi A novel three-dimensional framework of 2-[(1H -imidazol-1-yl)methyl]-1H -benzimidazole dihydrate, C11H10N4·2H2O or L·2H2O, (I), in which L acts as both hydrogen-bond acceptor and donor in the supramolecular construction with water, has been obtained by self-assembly reaction of L with H2O. The two independent water molecules are hydrogen bonded alternately with each other to form a one-dimensional infinite zigzag water chain. These water chains are linked by the benzimidazole molecules into a three-dimensional framework, in which each organic molecule is hydrogen bonded by three water molecules. This study shows that the diversity of hydrogen-bonded patterns plays a crucial role in the formation of the three-dimensional framework. More significantly, as water molecules are important in contributing to the conformation, stability, function and dynamics of biomacromolecules, the infinite chains of hydrogen-bonded water molecules seen in (I) may be a useful model for water in other chemical and biological processes. [source] Bonding in Tropolone, 2-Aminotropone, and Aminotroponimine: No Evidence of Resonance-Assisted Hydrogen-Bond EffectsCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2008Pablo Sanz Dr. Abstract The properties of the intramolecular hydrogen bond (IMHB) in tropolone, aminotropone, and aminotroponimine have been compared with those in the corresponding saturated analogues at the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory. In general, all those compounds in which the seven-membered ring is unsaturated exhibit a stronger IMHB than their saturated counterparts. Nevertheless, this enhanced strength is not primarily due to resonance-assisted hydrogen-bond effects, but to the much higher intrinsic basicity and acidity of the hydrogen-bond acceptor and donor groups, respectively, in the unsaturated compounds. These acidity and basicity enhancements have a double origin: 1),the unsaturated nature of the moiety to which the hydrogen-bond donor and acceptor are attached and 2),the cyclic nature of the compounds under scrutiny. As has been found for hydroxymethylene and aminomethylene cyclobutanones, and cyclobutenones and their nitrogen-containing analogues, the IMHB strength follows the [donor, acceptor] trend: [OH, CNH]>[OH, CO]>[NH2, CNH]>[NH2, CO] and fulfills a Steiner,Limbach correlation similar to that followed by intermolecular hydrogen bonds. [source] Nitrosyl Ruthenium Diolato ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2005Michael Barth Abstract [mer -(dien)(NO)Ru(AnErytH,2)]BPh4·2,H2O (1), [mer -(dien)(NO)Ru(R,R -ChxdH,2)]BPh4 (2), [mer -(dien)(NO)Ru(EthdH,2)]BPh4 (3), and [mer -(dien)(NO)Ru(Me-,- D -Ribf2,3H,2)]BPh4·5.5,H2O (4) have been synthesized in the form of light pink crystals by the reaction of [mer -(dien)(NO)RuCl2]X with the respective diol in aqueous sodium hydroxide solution (dien = diethylenetriamine, AnEryt = anhydroerythritol, Chxd = cyclohexane-1,2-diol, Ethd = ethanediol, Rib = ribose; X = BPh4 or PF6). The nitrosyl ligand exhibits a strong trans influence which causes the trans -bonded oxygen atom of the diolato ligand to form a shorter bond with the Ru centre. Mean values are 2.038 for cis and 1.946 Å for transO -binding. Back donation is strongly supported by the diolato ligand resulting in low energies for the N,O stretch which can be observed as low as 1805 cm,1. trans -Oxygen atoms do not act as hydrogen-bond acceptors in any of the cases. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Selecting the right compounds for screening: use of surface-area parametersPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 3 2002Colin M Tice Abstract Polar surface area, total surface area and percentage surface area have been calculated from three-dimensional structures of 88 post-emergence herbicides, 93 pre-emergence herbicides and 237 insecticides. Preferred ranges of values of these parameters were identified. Since the compounds in the training sets are used on a wide variety of species and target sites with various application modes, the parameter ranges are necessarily broad. The utility of the surface-area parameter ranges in selection of compounds for agrochemical screening was compared with the use of ranges of the Lipinski Rule of 5 parameters: molecular mass, calculated log P, number of hydrogen-bond donors and number of hydrogen-bond acceptors. The more computationally intensive surface-area parameters did not offer any obvious advantage over the Lipinski Rule of 5 parameters. © 2002 Society of Chemical Industry [source] Competition of hydrogen-bond acceptors for the strong carboxyl donorACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2001Thomas Steiner A database study on the competition of hydrogen-bond acceptors for the strong carboxyl donor in crystals is reported. The relative success in attracting this donor is determined for 34 types of acceptor (O, N, S, halogen and , acceptors), and a correlation between the success in competition and the average hydrogen-bond distance is established. [source] 2-(3-Hydroxypropyl)isoindoline-1,3-dione: competition among hydrogen-bond acceptorsACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Honghao Wang The title compound, C11H11NO3, has two molecules in the asymmetric unit, which differ in the orientation of their side-chain OH groups, allowing them to form intermolecular O,H...O hydrogen bonds to different acceptors. In one case, the acceptor is the OH group of the other molecule, and in the other case it is an imide O=C group. This is the first example in the N -substituted phthalimide series in which independent molecules have different types of acceptor. Molecular-orbital calculations place the greatest negative charge on the OH group. [source] Competing hydrogen-bond acceptors in ethylenediammonium oxotrithiotungstate(VI)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2007Bikshandarkoil R. Srinivasan The structure of the title compound, (C2H10N2)[WOS3], consists of ethylenediammonium dications and tetrahedral [WOS3]2, dianions, which are linked with the aid of four varieties of hydrogen bond, namely N,H,O, N,H,S, C,H,O and C,H,S. The strength and number of these hydrogen bonds affect the W,O and W,S bond distances. [source] Modulation of Stacking Interactions by Transition-Metal Coordination: Ab Initio Benchmark StudiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2010Shaun Abstract A series of ab initio calculations are used to determine the CH,,,, and ,,,,,-stacking interactions of aromatic rings coordinated to transition-metal centres. Two model complexes have been employed, namely, ferrocene and chromium benzene tricarbonyl. Benchmark data obtained from extrapolation of MP2 energies to the basis set limit, coupled with CCSD(T) correction, indicate that coordinated aromatic rings are slightly weaker hydrogen-bond acceptors but are significantly stronger hydrogen-bond donors than uncomplexed rings. It is found that ,,,,, stacking to a second benzene is stronger than in the free benzene dimer, especially in the chromium case. This is assigned, by use of energy partitioning in the local correlation method, to dispersion interactions between metal d and benzene , orbitals. The benchmark data is also used to test the performance of more efficient theoretical methods, indicating that spin-component scaling of MP2 energies performs well in all cases, whereas various density functionals describe some complexes well, but others with errors of more than 1,kcal,mol,1. [source] | ||||||||||