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sciforum-000004
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The Influence of Methyl Group Position on the Chemical Shifts Values of all Protons in the 1H NMR Spectra of Trimethylalkane Molecules
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N/A
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In our previous researches (see ECSOC-16, 2012 and ECSOC-17, 2013) we found the interesting dependencies of the protons chemical shift values in unsubstituted, mono- and dimethylsubstituted linear alkanes NMR 1H spectra upon the position of methyl group. In continuation of this topic we begin the investigation of the similar dependencies in trimethylsubstituted linear alkanes. In this paper we describe only four simplest families of trimethylalkanes. The position of the each methyl group in the alkyl chain of trimethylalkanes denoted by the symbol «N1, N2 and N3», indicating the number from the beginning of the chain of carbon atoms to which three "methyl substituents" are attached. For this purpose we have studied and analyzed the literature data of proton chemical shifts in the 1H NMR spectra of four "trimethylalkane families": 2,2,5- (N1 = 2; N2 = 2; N3 = 5); 2,2,4-; 2,2,3- and 2,3,4-trimetyllalkanes. We compared the protons chemical shift values (base spectral parameters) of the same type of protons. For example, for triprotonic signal of terminal methyl groups in the studied trimethylalkane on the one hand, with the studied earlier the same parameters of terminal methyl groups in a) unsubstituted linear alkane, b) monomethylalkane and c) dimethylalrane on the other hand. We fixed the differences between the compared chemical shifts (ie, differential spectral parameters) only for the cases when this difference is equal or exceeds a value equal to 0.02 ppm. These values of the differential spectral parameters we have identified as "significant" (ie, to be discussed). When researching all four families of N1,N2,N3-trimethylalkanes we reveal that only in the case of 2,2,5-trimethylalkane family the chemical shifts of all protons in molecule we can considered as the sum of two previously studied parameters of nonoverlapping pentacarbonic [С1Н12-С2(СН3)(СН3)–С 3Н 32-] and tetracarbonic [–С4H42-C5H5(C5'H5'3)-С6H62-] fragments. In the other two cases of 2,2,N3- trimethylalkanes, when both of these fragments overlap, depending on the relative position of the third methyl group in the molecule must be considered the "octacarbonic" fragment [С1Н13-С2(С2'Н2'3)(С2''Н2''3)–С3Н32-С4Н4(С4'Н4'3)–С5Н52-] as the whole moiety in 2,2,4-trimethylalkanes and "heptacarbonic" fragment [С1Н13-С2(С2'Н2'3)(С2''Н2''3)–С3Н3(С3'Н3'3)-С4Н42–] in 2,2,3-trimethylalkanes. Similarly in the case of last forth family of 2,3,4-trimethylalkanes we consider as the whole moiety another "octacarbonic" fragment [С1Н13-С2H(С2'Н2'3)–С3Н3(С3''Н3''3)-С4Н4(С4'Н4'3)–С5Н52-].We calculate and discuss the mean base and differential spectral parameter values for each protons type in these "polycarbonic fragments" in each of the studied trimethylalkane families.
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sciforum-000022
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An Efficient Procedure for Development of Levofloxain Hemihydrates Synthesis and Purification
Saeed Bagherpoor ,
Seyed Kiumars Hosseini ,
Ali Golmohammadi
Submitted: 04 Nov 2024
Abstract: Show Abstract
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Saeed Bagherpoor ,
Seyed Kiumars Hosseini ,
Ali Golmohammadi
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N/A
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Show Abstract
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Levofloxacin is a broad spectrum synthetic fluoroquinolone antibiotic and is used to treat infections including: respiratory tract infections, cellulites urinary tract infections, prostatis, endocarditis, meningitis, pelvic inflammatory disease, traveler's diarrhea, tuberculosis and plague. Levofloxacin is the S-enantiomer of a racemate, named ofloxacin.Many synthetic routes for preparing levofloxacin have been reported. Most of them involved using non-feasible reagents, high temperature during synthesis, non-recyclable, costly and poisonous solvents. Therefore, the selection of an inexpensive, recoverable and non-toxic medium for synthesis with high yield and also having minimum negative effect on the environment is of prime importance in industrial scale. Levofloxacin is produced by the reaction of (S)-(-)-9, 10-difluoro-3-methyl-7oxo-2, 3-dihydro7H-pyrido [1, 2, 3-de] [1, 4] benzoxazine-6-carboxylic acid with N-methyl piperazine in a polar solvent, preferably at a technically acceptable temperature to form levofloxacin in an industrially feasible yield. The pure levofloxacin is used as hemihydrates, which has the empirical formula of C18H20FN3O4 ½ H2O.Herein, we wish to investigate the effect of various solvent systems on the yield of reaction. Depends on the solvent to be used, different temperature and reaction time for synthesis is considered. The best solvent will be selected based on the comparison of the measured yields and also the ability of recovering it in order to use for next batches. Another aspect of the present research is to develop an efficient method for purification of crude levofloxacin and convert it to hemihydrates form, which is stable and can be used as an API (Active Pharmaceutical Ingredient). The selection of solvent and also the amount of water to be used in purification step in order to change crystalline structure is very important, which will be investigated in this section. The results show that using DMSO for synthesis and Ethanol/Water for purification step are the best choices.
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sciforum-000031
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Preparation, Characterization and Microwave Absorption Performance of Ba(Ni0.5Mn0.5ZrO)Fe10O19/ Polybutadiene Nanocomposite
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The magnetic materials, especially ferrites, are an important class of electromagnetic waves absorbers especially, at the range of gigahertz (GHz) frequency. Conventional absorptive materials such as metal powders and ferrites are high in density and have poor environmental stability, which restricts their usefulness in applications requiring light- weight mass . One way to overcome these problems is to use a suspending agent, which could enwrap magnetic nanocparticles and the PBD provides both electrostatic and steric repulsion against particle aggregation. Also fabrication of flexible and transparent shielding structures could widen the range of application.In this paper, Ba(Ni.5Mn0.5ZrO)Fe10O19/ Polybutadiene magnetic nanocomposite was fabricated successfully via sol-gel method and masking method. The samples were characterized using SEM, UV-visible, EDX, ATR, XRD and VSM analyses. Finally vector network analyzer was employed to determine the ability of composites in microwave absorption at the range of 8-12 GHz (X-band). The results demonstrated the transparent shielding products have considerable capability in attenuation of electromagnetic wave and a minimum reflection loss of 9.1 db was obtained at 10.4 GHz for ferrite/PBD 10wt%.
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sciforum-000046
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Triplet-Singlet Intersection at Hydrogen Transfer Stage in Reactions of Organic Sulfides Photooxidation
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N/A
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Methanethiol and hydrogen sulphide photooxidation reaction pathways contain stages of hydrogen transfer, after which intersection crossing supposed to be to achieve singlet products of the reaction. While studying this stages no minimum was found at the point near reactants in the singlet state. At the same time there is a minimum in the triplet state. Moreover energy of reactants in the singlet state exceeds energy in the triplet state. That observation allows us to suppose intersection between the singlet and the triplet potencial energy surfaces at the hydrogen transfer stage. It may increase chance of the triplet-singlet transition. Calculation of the potencial energy surface profiles, sliced along with the hydrogen transfer path for both the singlet and the triplet states, performed with UB3LYP 6-311G++(d) method of the density functional theory have showed both existence and reaction coordinate of intersection.
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sciforum-000056
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Synthesis and X-ray Crystal Structure of the Thiosemicarbazone L bis(4-N-Methyl-Thiosemicarbazone)-4,4'-Diacetylphenylmethane
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We report herein the synthesis of the tetradentate thiosemicarbazone ligand bis(4-N-methyl-thiosemicarbazone)-4,4'-diacetylphenylmethane, which is a suitable precursor in supramolecular chemistry for the preparation of helical metal complexes. This molecule has been characterized by microanalysis, mass spectrometry, IR and 1H and 13C NMR spectroscopies. Its crystal structure has also been analysed.
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