China
Africa
Explore chapters and articles related to this topic
Nuclear Magnetic Resonance
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
The situation of protons with close chemical shifts coupled to each other such as an AB spin system will give a pattern of two doublets, but the intensities are not 1:1 with the inner signals having larger intensity than the outer signals. However, the separation between the lines of each doublet is still the coupling constant J. If more than two protons of close chemical shift are coupled to each other, more complex patterns, often described as complex multiplets, are observed. Multiplets still provide useful structural information because they indicate the presence of coupled protons of similar chemical shift. The AB pattern and complex multiplet patterns result from what is called second-order effects. Second-order effects occur when the ratio of the chemical shift separation in hertz to the measured coupling constant is less than approximately 10. A more in-depth discussion of the types of coupled spin systems may be found in other manuscripts [38].
Basic Atomic and Nuclear Physics
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Further difficulties arose when the model was applied to the spectrum of more complicated atoms. In the spectra of more complicated atoms, multiplet structure is observed. Multiplets differ from fine structure lines in that lines of a multiplet can be widely separated. The lines of sodium with wavelengths of 589.593 nm and 588.996 nm are an example of a doublet. Triplets are observed in the spectrum of magnesium.
Symmetry, Spin, and Statistics, 1926-1930
Published in John C.D. Brand, Lines of Light, 2017
The classical idea of spin assumed that the electron was a tiny spherical charge in rotation about its center, therefore endowed with angular momentum and a magnetic moment. The hypothesis was successfully applied by Uhlenbeck and Goudsmit1 to spectral multiplets and the Zeeman effect. Classical spin was assimilated to quantum mechanics and statistics by Heisenberg and Pauli.
Stereoselective synthesis of trans-benzo[d]oxazolyl)phenyl substituted β-lactams decorated with C-3 thio/seleno rich motifs: synthetic intermediates for diverse heterocycles
Published in Journal of Sulfur Chemistry, 2023
Preety Saini, Shalu Thakur, Ankita Garg, S. S. Bari, Aman Bhalla
All solvents used were of LR grade. The solvents were distilled and dried prior to use by standard methods [25]. All the reactions were carried out under dry and deoxygenated nitrogen atmosphere. 1H and 13C NMR spectra were recorded on JEOL AL 300 MHz and BRUKER AVANCE II 400 MHz spectrometer in CDCl3 using TMS as an internal standard (400 MHz, 1H, 100 MHz, 13C, 300 MHz, 1H, 75 MHz, 13C). The following abbreviations are used to indicate the multiplicity in NMR spectra: s—singlet, d—doublet, t—triplet, q—quartet, m—multiplet. Coupling constants (J) are quoted in hertz. Infrared spectra were recorded using Thermo scientific Nicolet iS50 (FT-IR) spectrophotometer (υmax in cm–1). Melting points were determined in an open capillary on melting point apparatus Perfit GSI-MP-3. Elemental analysis for C, H and N atom was performed with Flash 2000 Organic elemental analyzer. The mass spectra (EI-MS) were obtained using a Waters Q-TOF Micromass (YB361) spectrometer (permissible % error = 5–10 ppm). All the reactions were monitored by thin layer chromatography (TLC) using precoated silica 60 F254, 0.25 mm aluminum plates (Merck) with visualization under UV light. Separation and purification of compounds was done by column chromatography performed on activated silica gel (Qualigen Chemicals, 60–120 mesh) using 10% ethyl acetate: hexanes as an eluant system.
Cholesterol-based nonsymmetric dimers comprising phenyl 4-(benzoyloxy)benzoate core: the occurrence of frustrated phases
Published in Liquid Crystals, 2021
Channabasaveshwara V. Yelamaggad, Sachin A. Bhat
The required chemicals such as 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, chromium trioxide, DCC (dicyclohexyl carbodiimide), cholesterol, 8-bromooctanoic acid 6-bromohexanoic acid and 5-bromovaleric acid 4-bromobutyric acid bought from Sigma-Aldrich were used as received. The commercial organic solvents used were distilled prior to use. The LR grade organic solvents used in synthesis were purified and dried following standard drying protocols. Thin-layer chromatography (TLC) was carried out using TLC plates consisting of a thin layer of silica gel (Merck, Kieselgel60, F254) on an aluminium foil support. This technique was used to monitor the progress/ completion of reactions, as well as for examining the purity of the intermediates. The spots on the eluted TLC were visualised by using UV light at 254 nm or KMnO4 stains. Column chromatography was carried out using glass columns loaded with either Merck silica gel (60–120/100–200 mesh) or neutral alumina. UV–Vis spectra were recorded using either a Perkin– Elmer’s Lambda 750, 2015 NIR spectrometer or a Perkin Elmer’s, Lambda 20 UV–Vis spectrophotometer. IR spectra of the samples were recorded on a Perkin–Elmer Spectrum 1000 FT-IR spectrometer. A Bruker AMX-400 spectrometer operating at 400 MHz was used to record room temperature 1H, and 13C NMR spectra of the sample (CDCl3 solution) were recorded using a Bruker AMX-400 spectrometer operating at 400 MHz for 1H and 100 MHz for 13C. Chemical shifts (δ) have been presented in parts per million (ppm) relative to TMS using the residual CHCl3 peak in CDCl3 solution as the internal standard; δ H 7.26 and δ C 77.0 relative to TMS. NMR peaks multiplicities are presented as s (singlet), d (doublet), t (triplet) and m (multiplet). Coupling constants (J) are given in Hertz (Hz). Elemental analysis was carried out using a Perkin Elmer Elemental Analyser Series II 2400 analyser. CD spectra were obtained with the help of a Jasco J-810 spectropolarimeter. The mesomorphic properties of the materials were evaluated using an Olympus BX50 (Model BX50F4) polarising optical microscope (POM), attached to a Mettler FP82HT hot stage (attached to FP90 central processor) as well as to a digital camera. Differential scanning calorimeter (DSC) traces were recorded at a scanning rate of 5°C/min using Perkin-Elmer Diamond DSC equipment that was calibrated before use, using pure indium as a standard. X-ray diffraction (XRD) measurements were undertaken with CuK∝ (λ = 0.15418 nm) radiation using a PANalytical Empyrean machine. The powder samples placed in Lindemann capillaries (0.5 mm diameter) were used for XRD.