Vibrational assignment, structure and intramolecular hydrogen bond study of 3-amino-1-phenyl-2-buten-1-one

Fourier transform infrared and Fourier transform Raman spectra of 3-amino-1-phenyl-2-buten-1-one and its deuterated analogue were recorded in the regions 400-4,000 and 150-4,000 cm(-1), respectively. Furthermore, the molecular structure and vibrational frequencies of title compound were investigated by a series of density functional theoretical, DFT, and ab initio calculations at the post-Hartree-Fock (MP2) level. Although, the calculated frequencies are generally in agreement with the observed spectra but the DFT results are in much better quantitative agreement with the observed spectra than the MP2 results. The observed wavenumbers were analyzed and assigned to different normal modes of vibration of the molecule. The calculated geometrical parameters show a strong intramolecular hydrogen bond with a N...O distance of 2.621-2.668 A. This bond length is shorter than that of its parent, 4-amino-3-penten-2-one (with two methyl groups in the beta-position), which is in agreement with spectroscopic results. The topological properties of the electron density contributions for intramolecular hydrogen bond in 3-amino-1-phenyl-2-buten-1-one and 4-amino-3-penten-2-one have been analyzed in term of the Bader theory of atoms in molecules (AIM). These results also support the stronger hydrogen bond in the title compound with respect to the parent molecule.     

An approach to estimate the energy and strength of the intramolecular hydrogen bond in different conformers of 4‐methylamino‐3‐penten‐2‐one

The molecular structure and intramolecular hydrogen bond energy of 32 conformers of 4‐methylamino‐3‐penten‐2‐one were investigated at MP2 and B3LYP levels of theory using the standard 6–31G** basis set and AIM analyses. Furthermore, calculations for all the possible conformations of 4‐methylamino‐3‐penten‐2‐one in water solution were also carried out at B3LYP/6–31G** level of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the ketoamine conformers of this compound are more stable than the other conformers (i.e., enolimine and ketoimine). This stability is mainly due to the formation of a strong N? H···O intramolecular hydrogen bond, which is assisted by π‐electrons resonance. Hydrogen bond energies for all conformers of 4‐methylamino‐3‐penten‐2‐one were obtained from the related rotamers method. The nature of intramolecular hydrogen bond existing within 4‐methylamino‐3‐penten‐2‐one has been investigated by means of the Bader theory of atoms in molecules, which is based on topological properties of the electron density. The results of these calculations support the results which obtained by related rotamers method. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Molecular structure and vibrational assignment of α‐chloro acetylacetone: A density functional theory study

The intramolecular hydrogen bond, molecular structure, and vibrational frequencies of α‐chloro acetylacetone have been investigated. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were recorded in the regions 400–4,000 cm^?1 and 50–4,000 cm^?1, respectively. Rigorous normal coordinate analysis has been performed at the B3LYP/6‐311++G** level of theory for purposes of comparison. The complete vibrational assignment for TFAA has been made on the basis of the calculated potential energy distribution. We also applied the atoms in molecules theory and natural bond orbital method for the analysis of the hydrogen bond in α‐Chloro acetylacetone and acetylacetone. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Intramolecular hydrogen bond, molecular structure and vibrational assignment of tetra-acetylethane. A density functional study

The intramolecular hydrogen bond, molecular structure and vibrational frequencies of tetra-acetylethane have been investigated by means of high-level density functional theory (DFT) methods with most popular basis sets. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were recorded in the regions 400-4000 cm(-1) and 40-4000 cm(-1), respectively. The calculated geometrical parameters of tetra-acetylethane were compared to the experimental results of this compound and its parent molecule (acetylacetone), obtained from X-ray diffraction. The O...O distance in tetra-acetylethane, about 2.424A, suggests that the hydrogen bond in this compound is stronger than acetylacetone. This conclusion is well supported by the NMR proton chemical shifts and O-H stretching mode at 2626 cm(-1). Furthermore, the calculated hydrogen bond energy in the title compound is 17.22 kcal/mol, which is greater than the acetylacetone value. On the other hand, the results of theoretical calculations show that the bulky substitution in alpha-position of acetylacetone results in an increase of the conjugation of pi electrons in the chelate ring. Finally, we applied the atoms in molecules (AIM) theory and natural bond orbital method (NBO) for detail analyzing the hydrogen bond in tetra-acetylethane and acetylacetone. These results are in agreement with the vibrational spectra interpretation and quantum chemical calculation results. Also, the conformations of methyl groups with respect to the plane of the molecule and with respect to each other were investigated.     

β‐Aminoacrolein: An ab initio,AIM and NBO study

The molecular structure and the intramolecular hydrogen bonding of β‐aminoacrolein and its simple derivatives were investigated at the MP2 and B3LYP levels of theory using the standard 6‐311++G(d, p) basis set. The “atoms in molecules” or AIM theory of Bader which is based on topological properties of the electron density (ρ), was used. Additionally, an analysis of the critical points was performed to study the nature hydrogen bonding in these systems. Natural bond orbital (NBO) analysis was also carried out for to better comprehend the nature of the intramolecular interactions in β‐aminoacrolein and its derivatives. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

N?H···S and S?H···N intramolecular hydrogen bond in β‐thioaminoacrolein: A quantum chemical study

The conformational study of β‐thioaminoacrolein was performed at various theoretical levels, HF, B3LYP, and MP2 with 6‐311++G(d,p) basis set, and the equilibrium conformations were determined. To have more reliable energies, the total energies of all conformers were recomputed at high‐level ab initio methods, G2MP2, G3, and CBS‐QB3. According to these calculations, the intramolecular hydrogen bond is accepted as the origin of conformational preference in thialamine (TAA) and thiolimine groups. The hydrogen bond strength in various resonance‐assisted hydrogen bond systems was evaluated by HB energy, geometrical parameters, topological parameters, and charge transfers corresponding to orbital interactions. Furthermore, our results reveal that the TAA tautomer has extra stability with respect to the other tautomers. The population analyses of the possible conformations by NBO predict that the origin of this preference is mainly due to the π‐electron delocalization in framework of TAA forms, especially usual π_C?C → π*_C?S and Lp (N) → π*_C?C charge transfers. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Photochemische Reaktionen von Cyclopentadienylbis(ethen)rhodium mit Phenanthren,Acenaphthylen und Triphenylen,sowie ungewöhnlicher H-Austausch zwischen η2-koordinierten Phenanthren- bzw. Acenaphthylen- und η5-Cyclopentadienyl-Liganden

Photochemical Reactions of Cyclopentadienylbis(ethene)rhodium with Phenanthrene, Acenaphthylene, and Triphenylene, and Unusual H Exchange between η²-Coordinated Phenanthrene or Acenaphthylene and η⁵-Cyclopentadienyl Ligands During UV irradiation of [CpRh(C₂H₄)₂] (Cp = η⁵-C₅H₅) in hexane/ether in the presence of phenanthrene one ethene ligand is displaced by coordination of the 9,10 double bond of phenanthrene, and (η⁵-cyclopentadienyl) (η²-ethene)(η²-9,10-phenanthrene)rhodium ( 1 ) is formed. The analogous reaction in hexane in the presence of acenaphthylene occurs with formation of the complexes (η²-1,2-acenaphthylene)(η⁵-cyclopentadienyl)(²-ethene)rhodium 2 and bis(η²-1,2-acenaphthylene)(η⁵-cyclopentadienyl)rhodium 3 in which one and two ethene molecules of [CpRh(C₂H₄)₂], respectively, are substituted by η²-1,2-acenaphthylene. The irradiation of [CpRh(C₂H₄)₂] with triphenylene in hexane yields the compounds [CpRh(η⁴-1,2,3,4-triphenylene)] ( 4 ), [(CpRh)₂(μ-η³: η³-triphenylene)] ( 5 ), and [(CpRh)₃(μ₃-η²: η²: η²-triphenylene)] ( 6 ). Despite the partially very low yields the new complexes could be unequivocally characterized spectroscopically and in the case of 1 and 3 by X-ray structural analysis. The compounds 1 and 2 in solution reveal a novel dynamic behaviour; via an intramolecular C? H activation, exchange occurs between the protons of the η²-coordinated arene and the Cp ligand. The complex 4 in solution is fluxional, too.     

NMR evidence for an NH+ …OC intramolecular hydrogen bond in 2-alkyl-3-morpholinopropiophenones—structure of a new elevated high density lipoprotein agent in solution

7-[2-(4-morpholinomethyl)butanoyl]-4-methyl-2H-1, 4-benzoxazin-3 (4H)-one hydrochloride (2a) (a new elevated high density lipoproteins agent) and related compounds have been studied by NMR spectroscopy. Compound 2a exhibits an intramolecular hydrogen bond between the NH⁺ and CO bonds in solvents with low nucleophilicity. These results are confirmed by IR spectroscopy in solution.     

Synthesis and Crystal Structure of 2-(4''-Methylphenoxy)-5,8,9-trimethyl-3-phenyl Thieno[3'',2'':5,6]pyrido[4,3-d]pyrimidin-4-(3H)-one Hydrochloride

The title compound 2-(4′-methylphenoxy)-5,8,9-trimethyl-3-phenyl thieno[3′,2′:5,6]pyrido[4,3-d]pyrimidin-4(3H)-one hydrochloride (C26H23Cl4N3O2S, Mr = 583.33) has been deter- mined by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/c with a = 14.8442(11), b = 11.5131(8), c = 17.2010(13) (A), β = 113.7250(10)o, V = 2691.3(3) (A)3, Z = 4, Dc = 1.440 g/cm3, S = 1.094, μ = 0.547 mm-1, F(000) = 1200, the final R = 0.0571 and wR = 0.1458. X-ray analysis reveals that the title compound combines with a molecule of dichloromethane by an intramolecular hydrogen bond. The thienopyridine ring is almost coplanar, and the dihedral angle between the thiophene plane and the pyridine plane is 0.6o.     

Synthesis and Crystal Structure of 3a-Hydroxy-3-phenyl-1,2,3,3a,8a-pentahydrocyclopenta[α]inden-8-one

The title compound 3a-hydroxy-3-phenyl-1,2,3,3a,8a-pentahydrocyclopenta[α]inden-8-one 2 (C18H16O2, Mr = 264.31) has been obtained by the treatment of 2-(3-iodopropyl)-2phenylindan-1,3-dione 1 with tributyltin hydride in refluxing benzene, and its crystal structure was determined by single-crystal X-ray diffraction. The analysis was carried out by direct and Fourier methods and the structure was refined by full-matrix least-squares computations. The title compound crystallizes in monoclinic, space group P21/n with a = 9.947(3), b = 10.336(3), c = 13.239(4) (A), β = 95.565(6)o, V = 1354.7(7) (A)3, Z = 4, Dc = 1.296 g/cm3, μ(MoKα) = 0.083 mm-1, F(000) = 560, the final R = 0.0749 and wR = 0.1191. X-ray analysis revealed that the bond length of O(2)C(12) is 1.219(2) (A), slightly longer than that of the normal C=O bond (1.119 (A)). The dihedral angle between planes II and III is almost 180°, while plane II is almost vertical to plane I consisting of C(1), C(3), C(4) and C(5) with the deviation of C(2) being 0.6269 (A). In addition, there exist intermolecular hydrogen bonds between O(2) and H(1)-O(1) in the crystal structure.     

Synthesis of 4-nitromethylene-1,4-dihydropyrimidine derivatives as pyrimidine nucleoside analogues

The synthesis of 4-nitromethylene-1,4-dihydropyrimidine derivatives as pyrimidine nucleoside analogues was developed, starting from 3-nitropyran-2-one N-functionalized amidines. Primary amines were reacted with amidines yielding 4-nitromethylene-1,4-dihydropyrimidine derivatives. In an initial survey, several 4-nitromethylene-1,4-dihydropyrimidines turned into 4-nitromethylene-1,2,3,4-tetrahydropyrimidine derivatives under different reduction conditions. The reduction reaction also induced a change in the exocyclic double bond configuration from (E) to (Z), due to an intramolecular hydrogen bond.     

Vibrational assignment of 4-amino-3-penten-2-one

The infrared and Raman spectra of 4-amino-3-penten-2-one and its two deuterated analogous have been measured. Comparison between the spectra recorded with two techniques, density functional theory (DFT) calculations and the spectral behavior upon deuteration was used for assignment of the vibrational spectra of the titled compound. DFT suggests a relatively strong intramolecular bent hydrogen bond with N...O distance in the range of 2.64-2.67 A, which is in agreement with the observed vNH at 3180 cm(-1). Existence of an intermolecular hydrogen bond is also shown in both solid and solution phases. The spectroscopic data support the enamine structure for this compound rather than imine structure.     

Crystal and molecular structures of (3Z)-(±)-4-(2′-hydroxypropyl)amino-and (3Z)-4-(2′-hydroxyethyl)amino-pent-3-en-2-ones

An X-ray study of (3Z)-(±)-4-(2′-hydroxypropyl)amino-and (3Z)-4-(2′-hydroxyethyl)amino-pent-3-en-2-ones is reported. The bond lengths inside the H ring are equalized due to the classical N-H...O hydrogen bond between the carbonyl oxygen and the amino group. In the 4-(2′-hydroxyethyl)amino-pent-3-en-2-one crystal, due to the classical N-H...O bonds, infinite zigzag chains are formed along the 0b axis and arranged into a layered structure due to the weak C-H...O interactions. In (±)-4-(2′-hydroxypropyl)aminopent-3-en-2-one crystal, however, centrosymmetric dimers are formed, which are then linked by weak C-H...O intermolecular interactions to form a layered structure along the a0b plane.     

A C-H...O=C hydrogen bond? Intramolecular hydrogen bonding in a novel semirubin.

(4Z)-8-(5-Carboxypentyl)-9-butyl-2,3-diethyl-dipyrrin-1-one (1), a new analogue of xanthobilirubic acid, (4Z)-8-(carboxyethyl)-2,7,9-dimethyl-3-ethyl-dipyrrin-1-one, was synthesized in four steps from the known 2,3-diethyl-dipyrrin-1-one. Whereas xanthobilirubic acid (which is a model for one-half of bilirubin, the yellow pigment of jaundice) and its homologues with hexanoic and longer acid chains at C-8 engage only in intermolecular hydrogen bonding, 1 is found to engage in intramolecular hydrogen bonding. In CDCl(3) solution, dipyrrinone 1 adopts an anti-Z conformation, and its hexanoic acid COOH is hydrogen-bonded to the lactam H-N-C=O and to the pyrrole C(7)-H but not to the pyrrole NH. The latter constitutes an example of a hydrogen bond of the type C-H...O=C, weak and detected typically in crystals. Dipyrrinone 1 is found by vapor pressure osmometry to be monomeric in CHCl(3), but its methyl ester (2) tends toward being dimeric, like that of methyl xanthobilirubinate, which is dimeric.     

The presentation of an approach for estimating the intramolecular hydrogen bond strength in conformational study of β-Aminoacrolein

All the plausible conformations of β-aminoacrolein (AMAC) have been investigated by the Bekes-Lee-Yang-Parr (B3LYP) nonlocal density functional with extended 6-311++G** basis set for studying the stability order of conformers and the various possibilities of intramolecular hydrogen bonding formation. In general the ketoamine (KA) conformers of AMAC, by mean average, are more stable than the corresponding enolimine (EI) and ketoimine (KI) analogues and this stability is mainly due to the π-electron resonance in these conformers that established by NH2 functional group. The contribution of resonance to the stability of chelated KA conformers is about 75.6 kJ/mol, which is greater than that of the hydrogen bond energy (E_HB=35.0 kJ/mol). The relative decreasing order of the various hydrogen bond energies was found to be: O–HN_imine(strong)>N_amine-HO_keto (normal)>N_imine-HO_hydroxyl (weak) > N_imine-HO_keto (weak). Hydrogen bond energies for all systems were obtained from the method that we called related rotamers method (RRM). The topological properties of the electron density contributions for various type of intramolecular hydrogen bond have been analyzed in term of the Bader theory of atoms in molecules (AIM). The results of these calculations support the previous calculations, which obtained by the related rotamer methods.     

Conformational structure of peptides containing dehydroalanine: Formation of β‐bend ribbon structure

α,β‐Unsaturated amino acids (dehydroamino acids) have been found in naturally occurring antibiotics of microbial origin and in some proteins. Due to the presence of the C_αC_β double bond, the dehydroamino acids influence the main‐chain and the side‐chain conformations. The lowest‐energy conformational state of the model tripeptides, Ac–X–ΔAla–NHMe, (X=Ala, Val, Leu, Abu, or Phe) corresponds to ϕ₁=−30°, ψ₁=120° and ϕ₂=ψ₂=30°. This structure is stabilized by the hydrogen bond between CO of the acetyl group and the NH of the amide group, resulting in the formation of a 10‐membered ring. In the model heptapeptide containing ΔAla at alternate position with Ala, Abu, and Leu, the lowest‐energy conformation corresponds to ϕ=−30° and ψ=120° for all the Ala, Abu, and Leu residues and ϕ=ψ=30° for all ΔAla residues. A graphical view of the molecule in this conformation reveals the formation of three hydrogen bonds involving the CO moiety of the ith residue and the NH moiety of the i+3th residue, resulting in a 10‐membered ring formation. In this structure, only alternate peptide bonds are involved in the intramolecular hydrogen‐bond formation unlike the helices and it has been named the β‐bend ribbon structure. The helical structures were predicted to be the most stable structures in the heptapeptide Ac–(Aib–ΔAla)₃–NHMe with ϕ=±30°, ψ=±60° for Aib residues and ϕ=ψ=±30° for ΔAla residues. The computational results reveal that the ΔAla residue does not induce an inverse γ‐turn in the preceding residue. It is the competitive interaction of small solvent molecules with the hydrogen‐bonding sites of the peptide which gives rise to the formation of an inverse γ‐turn (ϕ₁=−54°, ψ₁=82°; ϕ₂=44°, ψ₂=3°) in the preceding residue to ΔAla. The computational studies for the positional preference of ΔAla in the peptide containing one ΔAla and nine Ala residues reveals the formation of a 3₁₀ helical structure in all the cases with the terminal preferences for ΔAla, consistent with the position of ΔAla in the natural antibiotics. The extended structures is found to be the most stable for poly‐ΔAla. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 15–23, 1999     

Synthesis and Crystal Structure of 2-(4’-Methylphenoxy)-5,8,9-trimethyl-3-phenyl Thieno[3′,2′:5,6]pyrido[4,3-d]pyrimidin-4-(3H)-one Hydrochloride

1 INTRODUCTION Pyrido[4,3-d]pyrimidine derivatives have pharma- ceutical activity and germicidal action[1~3]. So far, hundreds of tetrahydro- and octahydro-pyrido[4,3- d]pyrimidines have been synthesized as potential diuretic, antirheumatic and bacteriostatic drugs, but only a few of fully aromatic pyrido[4,3-d] pyrimi- dines are known. An important synthetic route to synthesize fully aromatic pyrido[4,3-d]pyrimidines is the condensation reaction of 4-aminonicotinic acid and amines[4]. Ho…     

Reactions of 3, 5-Dimethyl-4-Carbethoxy-2-Cyclohexen-1-One at α-Position

3, 5-Dimethyl-4-carbethoxy-2-cyclohexen-1-one has been synthesized through the Knoevenagel condensation¹, which is then subjected to alkylation and acylation at α-position. The resulting products are hydrolyzed and decarboxylated to α-substituted cyclohexenones. 3, 5-Dimethyl-2-cyclohexen-1-one is converted by N-bromosuccinimide to phenol via enolization².     

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one by Hartree-Fock and density functional theory calculations

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one (C(11)H(13)N(3)O(2)) in the ground state have been investigated by Hartree-Fock and density functional method (B3LYP and BLYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of title compound and calculated results by HF and DFT methods indicate that B3LYP is superior to the scaled HF approach for molecular problems.     

Photolysis of α,β‐Epoxyketones: A Green Synthesis of β‐Hydroxyenones through Tandem H‐Abstraction,Ring Cleavage and Isomerisation

The photochemical behavior of various substituted epoxycarbonyl compounds consisting of more than one possible photo‐labile site (i.e. δ‐hydrogen, β‐hydrogen and epoxide ring) has been investigated. These compounds on photo‐irradiation produced the β‐hydroxyenones in an eco‐friendly green approach. Mechanistically, these photo‐transformations have been envisaged to occur via an intramolecular β‐hydrogen abstraction by the carbonyl group of benzoyl moiety to generate the 1,3‐biradical followed by epoxide ring opening that isomerizes into the photoproducts. The photolysis of the probed epoxy ketones didn’t furnish any photoproduct through δ‐hydrogen abstraction, whatsoever. This exclusive preference for β‐H abstraction over δ‐H abstraction by carbonyl group has been vindicated by the MM2 energy mini‐ mized program for the investigated photochemical substrates. The structures of these photoproducts were established from the analysis of their spectral parameters (IR, ¹H/¹³C NMR and Mass) and single crystal X‐ray crystallography data.