Study of Hydrogen Bonding in Nitro Enamides (original) (raw)
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Vibrational Spectroscopy, 2020
The synthesis and molecular structure of 3-nitroso-2,4-pentanedione, entitled to oxime-acetylacetone (oxime-AA), was studied utilizing Density Functional Theory (DFT) calculations and the results were compared with those of 3-nitro-pentane-2,4-dione (NO 2 AA) and 2-nitromalonaldehyde (NO 2 MA). The vibrational frequencies of the most stable cis-enol form were calculated using the B3LYP functional and 6-311++G(d,p) basis set. The calculated frequencies and chemical shifts of oxime-AA were compared with the experimental results. The calculated geometrical parameters for oxime-AA show a medium hydrogen bond compared with their α-substituted (NO 2 AA) and (NO 2 MA) which manifested the strong hydrogen bond. The calculated O⋯O distance of 2.460-2.561 Å is about 0.002-0.104 Å longer than in NO 2 AA and NO 2 MA. According to the theoretical calculations, oxime-AA has a structure with a hydrogen bond strength of about 21.0 kcal/mol (calculated with 6-311++G(d,p) basis set), which is 4.0-6.0 kcal/mol weaker than the hydrogen bond strength of NO 2 AA and NO 2 MA. This decrease in the hydrogen bond strength is also consistent with the experimental results. Natural Bond Orbital (NBO) and AIM analyses were applied for considering the hydrogen bond strength in oxime-AA that indicates the effect of NOH group decreases the hydrogen bond strength.
The influence of the substituent at the C2 position on the hydrogen-bonding patterns is compared for a series of five related compounds, namely (+-)-3-exo,6-exo-dibromo-5-endo- hydroxy-3-endo-nitrobicyclo[2.2.1]heptane-2-exo-carbonitrile, C8H8Br2N2 O3, (II), (+-)-3-exo,6-exo-dibromo-6-endo-nitro-5- exo-phenylbicyclo[2.2.1]heptan-2-endo-ol, C13H13Br2NO3, (III), (+-)-methyl 3-exo,6-exo-dibromo-5-endo-hydroxy-3-endo-nitro- bicyclo[2.2.1]heptane-2-exo-carboxylate, C9H11Br2NO5, (IV), (+-)-methyl-3-exo,6-exo-dibromo-7-diphenylmethylidene-5- endo-hydroxy-3-endo-nitrobicyclo[2.2.1]heptane-2-exo-carbox- ylate, C22H19Br2NO5, (V), and (+-)-methyl-3-exo,6-exo- dibromo-5-endo-hydroxy-3-endo-nitro-7-oxabicyclo[2.2.1]heptane-2-exo-carboxylate, C8H9Br2NO6, (VI). The hydrogen bonding motif in all five compounds is a chain, formed by O—H...O hydrogen bonds in (III), (IV), (V) and (VI), and by O—H...N hydrogen bonds in (II). All compounds except (III) contain a number of Br...Br and Br...O halogen bonds that connect the chains to each other to form two-dimensional sheets or three-dimensional networks. None of the compounds features intramolecular hydrogen bonding between the alcohol and nitro functional groups, as was found in the related compound (+-)-methyl 3-exo,6-exo-dichloro-5-endo-hydroxy-3-endo-nitrobicyclo[2.2.1]heptane-2-exo-carboxylate, (I) [Boeyens, Denner & Michael (1984b). J. Chem. Soc. Perkin Trans. 2, pp. 767–770]. The crystal structure of (V) exhibits whole-molecule disorder.
The nitro group is active in metabolic systems and can be found as an integral part of a number of useful curative drugs and many toxic substances. The basis for much of this activity is not fully understood. It is not necessarily caused directly by through-bond electronic effects but may also be due to direct H-bonding to nitro or to indirect interference by the nitro group with existing H-bonding. An unusual effect of a nitro substituent on kinetic results from urethane addition/elimination reactions (Scheme 1) has been ascribed to some form of self-association, which was neither specified nor quantified. To investigate self-association phenomena caused by a nitro group, a bond energy/bond order formula for NO bonds has been developed and then used to interpret relative amounts of covalent and ionic contributions to total NO bond energy. Calculated bond energies were then used to obtain enthalpies of formation for H-bonds to nitro groups in crystals and in solution. Similar results from solution data reveal that direct H-bonding to nitro is much weaker than in crystals, unless intramolecular H-bonding can occur. The results revealed that the 'self-association' effects observed for nitro substituents in urethanes (Scheme 1) were not caused by nitro participating directly in intermolecular bonding to NH of another urethane but by an indirect intramolecular action of the nitro group on pre-existing normal NH-O amide/amide type H-bonding.
Arkivoc, 2009
The nitro group is active in metabolic systems and can be found as an integral part of a number of useful curative drugs and many toxic substances. The basis for much of this activity is not fully understood. It is not necessarily caused directly by through-bond electronic effects but may also be due to direct H-bonding to nitro or to indirect interference by the nitro group with existing H-bonding. An unusual effect of a nitro substituent on kinetic results from urethane addition/elimination reactions (Scheme 1) has been ascribed to some form of self-association, which was neither specified nor quantified. To investigate self-association phenomena caused by a nitro group, a bond energy/bond order formula for NO bonds has been developed and then used to interpret relative amounts of covalent and ionic contributions to total NO bond energy. Calculated bond energies were then used to obtain enthalpies of formation for H-bonds to nitro groups in crystals and in solution. Similar results from solution data reveal that direct H-bonding to nitro is much weaker than in crystals, unless intramolecular H-bonding can occur. The results revealed that the 'self-association' effects observed for nitro substituents in urethanes (Scheme 1) were not caused by nitro participating directly in intermolecular bonding to NH of another urethane but by an indirect intramolecular action of the nitro group on pre-existing normal NH-O amide/amide type H-bonding.
The C—H⋯O hydrogen bond. An ab initio study of nitrosomethane and its hydrogen bonded dimer
Journal of Molecular Structure, 1975
In order to study the short C-H * *. 0 contact which has been found in several nitroso compounds, a series of ab initio calculations have been performed on nitrosomethane and it's cyclic "hydrogen bonded" dimer. A potential function for the C-H * * l 0 contact has been found and the effect of this contact upon the NO and CN bonds has been studied. The potential is shallow with a minimum of only-2.65 kcal mol-' for each contact and the equilibrium C-0 distance is 3.524, A. These results indicate that the C-H * .-0 bond is better described as a van der Waal's type contact than a hydrogen bond. The equilibrium length of the NO bond (RNo) changes in a regular manner with variations in the C-s * 0 (R,,,) distance, i.e. when R,,, becomes shorter R,, becomes longer. However, the variations in the CN bond lengths, which in the nitrosomethane monomer molecule is a long and weak bond, are anomalous.
Acta Crystallographica Section B Structural Science, 2005
The six isomeric N-(iodophenyl)nitrophthalimides, C 14 H 7 IN 2 O 4 , have been synthesized and the structures of five of them are reported. In N-(4-iodophenyl)-4-nitrophthalimide [(I), orthorhombic P2 1 2 1 2 1 ] the molecules are linked into sheets by a combination of four independent C-HÁ Á ÁO hydrogen bonds, but IÁ Á ÁO interactions are absent. The isomers N-(3-iodophenyl)-4-nitrophthalimide [(II), monoclinic P2 1 /c] and N-(2-iodophenyl)-4-nitrophthalimide [(III), monoclinic P2 1 /n] both form sheets, but in (II) the molecules are linked by a combination of one two-centre iodoÁ Á Ánitro interaction and one C-HÁ Á ÁO hydrogen bond into sheets containing R 4 4 ð30Þ rings, while in (III) they are linked by an iodoÁ Á Ácarbonyl interaction and a C-HÁ Á ÁO hydrogen bond into sheets or R 4 4 ð26Þ rings. Three-dimensional supramolecular structures are formed in both N-(4-iodophenyl)-3-nitrophthalimide [(IV), monoclinic P2 1 /n] and N-(3-iodophenyl)-3nitrophthalimide [(V), orthorhombic, P2 1 2 1 2 1 ]. In (IV) the molecules are linked by a three-centre iodoÁ Á Ánitro interaction, three C-HÁ Á ÁO hydrogen bonds and an aromatic Á Á Á stacking interaction, but the framework in (V) is generated by a two-centre iodoÁ Á Ánitro interaction and only two C-HÁ Á ÁO hydrogen bonds: aromatic Á Á Á stacking interactions are absent from (V).
Journal of Chemical Crystallography, 2016
The single crystal X-ray structures of 2-nitrophenylacetylene, 1, and 4,5-dimethyl-2-nitrophenylacetylene, 2, are presented. In both structures the nitro moiety is essentially coplanar with the benzene ring and interacts with the proximal alkyne which is slightly distorted. The crystal packing of both compounds is dominated by intramolecular alkyne-nitro C-HÁÁÁO hydrogen bonds that are supplemented by weak arene C-HÁÁÁO (nitro) hydrogen bonds. Compound 1 crystallizes in the monoclinic space group P21/c with a = 3.7874(5), b = 13.0673(16), c = 13.98174(17) Å , b = 90.587(2) and Z = 4. The molecule is disordered over two sites with occupancy ratio of 88:12. Compound 2 crystallizes in the triclinic space group P-1 with a = 7.6080(5), b = 9.8811(6), c = 12.8240(8) Å , a = 108.1760(10), b = 102.4170, c = 96.6480(10) and Z = 4. The intermolecular interactions in both structures were dominated by alkyne-nitro and arene-nitro C-HÁÁÁO hydrogen bonds.