Vibrational assignment, structure and intramolecular hydrogen bond of 4-methylamino-3-penten-2-one

The molecular structure, intramolecular hydrogen and vibrational frequencies of 4-methylamino-3-penten-2-one were investigated by a series of density functional theoretical (DFT) calculations and ab initio calculation at the post-Hartree-Fock (MP2) level. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were clearly assigned. The calculated geometrical parameters show a strong intramolecular hydrogen bond with a N...O distance of 2.622-2.670 A. This bond length is about 0.02 A shorter than that in its parent, 4-amino-3- penten-2-one which is in agreement with spectroscopic results. Furthermore, the conformations of methyl groups with respect to the plane of the molecule and with respect to each other were investigated.     

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.     

Vibrational spectra and structure of 4-amino-1H-quinazolin-2-one 3-oxide

On the basis of a study of the vibrational spectra in the solid state of the product of the reaction of 2-cyanophenyl isocyanate with hydroxylamine and its isotopic analogs (¹⁵N O and ¹⁵NH₂) it was demonstrated that the compound obtained has the 4-amino-1H-quinazolin-2-one 3-oxide structure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 968–972, July, 1981.     

Synthesis of 1-Bromo-3-butyn-2-one and 1,3-Dibromo-3-buten-2-one

Synthetic procedures for the preparation of 1-bromo-3-butyn-2-one and 1,3-dibromo-3-buten-2-one are given. These compounds are prepared from 2-bromomethyl-2-vinyl-1,3-dioxolane, which can readily be prepared from 2-ethyl- 2-methyl-1,3-dioxolane. The synthetic routes are as follows: 2-bromomethyl-2-vinyl-1,3-dioxolane is converted to 2-(1,2-dibromoethyl)-2-bromomethyl-1,3-dioxolane. Double dehydrobromination with ^tBuOK affords 2-ethynyl-2-bromomethyl-1,3-dioxolane. Formolysis with formic acid gives 1-bromo-3-butyn-2-one. Deacetalized 2-bromoethyl-2-vinyl-1,3-dioxolane was treated with Br₂ and Li₂CO₃/12-crown-4 in tetrahydrofuran to give 1,3-dibrom-3-buten-2-one in moderate yield.     

Improved Synthesis of 1-Bromo-3-buten-2-one

A convenient procedure for the synthesis of 1-bromo-3-buten-2-one, 4, from commercially available 2-ethyl-2-methyl-1,3-dioxolane, 1, is described. The procedure involves three reaction steps: (1) The acetal 1 is converted to 2-(1-bromoethyl)-2-bromomethyl-1,3-dioxolane, 2, by reacting 1 with elemental bromine in dichloromethane to yield 98% of 2. (2) Dehydrobromination of 2 with potassium tert-butoxide in tetrahydrofuran gives 2-bromomethyl-2-vinyl-1,3-dioxolane, 3, in 84–93% yield. (3) Removal of the acetal protection from 3 by formolysis for 6–10 h afforded 1-bromo-3-buten-2-one, 4, in 85–94% yield. A more rapid method is acid hydrolysis of 3 under microwave activation (100 °C, 8–10 min), by which 4 was obtained in 75% yield. Full experimental details are given.

The conformational composition of 3-buten-1-ol, the importance of intramolecular hydrogen bonding

The conformations of 3-buten-1-ol (1), and its model compounds cis-6-methyl-3-cyclohexen-1-ol (6), 3-cyclopenten-1-ol (7) and epicholesterol (9) have been investigated by FT-IR and ¹H NMR spectroscopy. The energies and geometries of 1, 6 and 7 were also investigated by molecular mechanics, semiempirical molecular orbital and ab initio calculations, while 9 was investigated by molecular mechanics only. The objective of the work was to study the conformational composition and importance of intramolecular OH…π hydrogen bonding for this composition in 1. Only two conformers of 1 have a geometrical possibility for intramolecular hydrogen bonding: Conformers 12 and 13 (Fig. 1). Compounds 6 and 7 were used as models for Conformer 12, while 9 was used as a model for Conformer 13. The investigations showed that Conformer 13 is the only hydrogen-bonded conformer, and that Conformer 12 is not intramolecularly hydrogen bonded. Conformer 13 was the most populated conformer, while Conformer 12 was hardly populated. The combination of experimental and theoretical data, and the use of model compounds was found necessary to obtain this conclusion.     

Synthesis,structure, and transformation of 1-amino-5-phenyl- 2,6,6-tricyano-3-cyclopropyl-1, 3-cyclohexadiene into 6-phenyl-2-dicyanomethylene-3-cyano-4-cyclopropyl-1, 2-dihydropyridine

1-Amino-5-phenyl-2,6,6-tricyano-3-cyclopropyl-1,3-cyclohexadiene is prepared by reaction of benzylidenemalononitrile with (1-cyclopropylethylidene) malononitrile. According to x-ray structural data, steric effects of the cyclohexadiene cause the C¹-C⁶ and C⁵-C⁶ bond lengths to increase to 1.541(3) and 1.568(3) Å. The weakest bond of the cyclohexadiene, C⁵-C⁶, ruptures homolytically on external energy deposition with subsequent formation of a substituted dihydropyridine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2776–2780, December, 1989.     

The structure of 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one

Crystal and molecular structure of 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one as a product of the benzoylation of 1-phenyl-3-benzoylaminopyrazol-2-in-5-one was characterised by X-ray single crystal diffraction. It is shown that 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one exists in the solid phase in an NH-tautomeric form, which is stabilised by two intramolecular hydrogen bonds and one intermolecular bond with the solvate dioxane molecule, the latter being used as a solvent for recrystallisation.     

Vibrational relaxation and coupling of two OH-stretch oscillators with an intramolecular hydrogen bond

We studied the vibrational dynamics of the OH-stretch oscillators of an alcohol with two vicinal OH groups using femtosecond midinfrared pump-probe spectroscopy. The absorption spectrum of pinacol (2,3-dimethyl-2,3-butanediol) in CDCl3 shows two OH-stretch peaks belonging to hydrogen bonded and free OH groups. The anharmonicities of the hydrogen-bonded and free OH-stretch vibrations are 180 and 160 cm(-1), respectively. The lifetime T1 of the OH-stretch vibration is found to be 3.5 +/- 0.4 ps for the hydrogen bonded and 7.4 +/- 0.5 ps for the free OH group. We observed sidebands in the transient spectra after excitation of the bonded OH group, which we attribute to a progression in a low-frequency hydrogen-bond mode. The sideband is redshifted 60 cm(-1) with respect to the 0 --> 1 transition. Due to the coupling between the two OH groups and the presence of the sidebands, simultaneous excitation of both OH-stretch vibrations leads to oscillations on the pump-probe signal with frequencies of 40 and 60 cm(-1).     

Molecular structure of dipivaloylmethane and the intramolecular hydrogen bond problem

Molecular structure of dipivaloylmethane was investigated by X-ray electron diffraction at 24°C. The C_2v and C_s geometrical models involving an intramolecular hydrogen bond are considered. The C_2v model with enol hydrogen lying symmetrically relative to the oxygen atoms has several advantages over the classical model of the enol tautomer. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 58-66, January–February, 2000     

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.     

An expedient synthesis of 3-amino-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one

Racemic 3-amino-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, 2, was prepared in four steps utilizing a novel mercuric ion assisted ammonia displacement of an N-acyl alkylthioglycine amide 5.     

Alkyldithiocarboxylation of 3-hydroxy-1-phenyl-2-pyrazolin-5-one

4-Alkyldithiocarboxylate-3,5-dihydroxy-1-phenylpyrazoles 2, are prepared in good yield by the reaction of 3-hydroxy-1-phenyl-2-pyrazolin-5-one 1 with sodium acetate in dimethylformamide (DMF), carbon disulfide and alkyl halides.     

O-Alkylation of 3-hydroxy-1-phenyl-2-pyrazolin-5-one

3-Hydroxy-1-phenyl-2-pyrazolin-5-one 1 reacts with primary, secondary and allylic alcohols under catalytic acidic conditions and in the presence of 3 Å molecular sieves, to afford 3-alkoxy-1-phenyl-2-pyrazolin-5-ones 3 .     

5-芳酰氨基-2-苯基-2H-1, 2, 4-噻二唑-3-酮的合成

用1-芳酰基-5-苯基-2-硫代双脲与溴进行氧化成环反应制备了九个新的5-芳酰氨基-2-苯基-2H-1, 2, 4-噻二唑-3-酮, 相应的1-芳酰基-5-苯基-2-硫代双脲可以通过苯基脲与酰基异硫氰酸酯加成制得。     

Synthesis of 1-amino-5-phenyl-4,5-dihydro-3H-2-benzazepines and the isomeric 2-amino-1-benzazepines

The title amidines (1 and 2) were synthesized. A synthesis of lactam 10 free of isomeric 4 is described. An interesting rate difference in displacement of thiomethyl ether intermediates 5 and 11 with amines was observed.     

Microwave spectra of isotopic glycolaldehydes,substitution structure,intramolecular hydrogen bond and dipole moment

The microwave spectra of ¹³CH₂OH-CHO, CH₂OH-¹³CHO, and CH₂OH-CH¹⁸O are reported and have been used in combination with previously published data on other monosubstituted glycolaldehydes to determine the substitution structure of the molecule as r(CO) = 1.209 Å, r(C-O) = 1.437 Å, r(C-C) = 1.499 Å, r(O-H) = 1.051 Å, r(C-H_ald) = 1.102 Å, r(C-H_alc) = 1.093 Å, r(O β H) = 2.007 Å, r(O β O) = 2.697 Å, ∠(C-CO) = 122°44', ∠(C-C-H_ald) = 115°16', ∠(C-C-O) = 111°28', ∠(C-O-H) = 101°34', ∠(C-C-H_alc) = 109°13', ∠(H-C-H) = 107°34', ∠(O-H β O) = 120°33', ∠(H β OC) = 83°41', and ∠(O-H, C0) = 24°14'. The intramolecular hydrogen bond and the other structural parameters are discussed and compared to related molecules. The dipole moment is redetermined to be μ_a = 0.262 ±0.002 D, μ_b = 2.33 ± 0.01 D, and μ_tot = 2.34 ± 0.01 D. Relative intensity measurements yielded 195 ± 30 cm^?1 for the C-C torsional fundamental and 260±40 cm^?1 for the lowest in-plane skeletal bending mode. Computations performed by the CNDO/2 method correctly predict the observed cis hydrogen-bonded conformer to be the energetically favoured one and in addition yield some indication of the existence of at least two other non-hydrogen-bonded forms of higher energy.