Chloroform chemical shift

Methyl chloride Methylene chloride Chloroform Chemical shift (8) 3.1 5.3 7.3... 

The proton magnetic spectrum is shown in Figure 2 (13). This spectrum was obtained on a Bruker Instruments Model AM-300 NMR spectrometer using a 4% w/v solution of lovastatin in deuterated chloroform. Chemical shifts (S) are expressed as ppm downfield from tetramethylsilane (internal standard). The tabulated signal assignments refer to the numbered structure of lovastatin shown below. 

Calcium chloride Deuterated chloroform Chemical-shift correlation spectroscopy... 

The proton affinities (gas phase) of thiirane and other three-membered heterocycles have been determined azirane (902.5), thiirane (819.2), phosphirane (815.0), oxirane (793.3 kJ moF ) (80JA5151). Increasing s character in the lone electron pairs decreases proton affinities. Data derived from NMR chemical shifts in chloroform indicate the order of decreasing basicity is azirane > oxirane > thiirane (73CR(B)(276)335). The base strengths of four-, five- and six-membered cyclic sulfides are greater than that of thiirane. 

FIGURE 13.7 The200-MHz H NMR spectrum of chloroform (HCCb). Chemical shifts are measured along the x-axis in parts per million (ppm) from tetramethylsilane as the reference, which is assigned a value of zero. 

Figure 2 compares the results of theory and experiment for the specific case of p-fluoronitrobenzene. Inspection of the calculated structure shows that the proton is still on the zeolite, and the F shifts are more like chloroform solution than superacid solution. Furthermore, when the l F chemical shift was calculated for the theoretical structure, it was found to agree with the experimental result. 

Spectroscopic Analysis. Infrared (IR) spectroscopic analysis was performed on a Beckman Microlab 620 MX computing spectrometer. Samples were cast on a sodium chloride pellet or made into a pellet with potassium bromide. and 13C NMR spectra were obtained using a JEOL HNM-FX 270 MHz Fourier transform NMR spectrometer. Samples were dissolved in deuterium chloroform and chemical shifts were referenced to an internal standard of tetramethylsilane. 

A phenomenological study was performed to determine the effect of solvent on Sn NMR spectra of these organoraetallic polymers. Samples were dissolved in chloroform, benzene, n-hexane, acetone, tetrahydrofuran, methanol, and pyridine. The Sn NMR spectra in these solvents are given in Figure 1. The appearance and location of the H Sn resonance changes drastically over the range of selected solvents. The chemical shift moves upfield in the order chloroform, benzene, n-hexane, acetone, tetrahydrofuran, pyridine, and methanol. The amount of structural information and, conversely, the broadening of the resonance increases in the same order with methanol and pyridine reversed. 

In donating solvents the subtle effects determining the chemical shift in chloroform, benzene, and hexane are apparently masked. In hexane, which is considered a poor solvent, self-association is possible and would explain the appearance of the Sn spectrum. Chloroform and benzene are excellent solvents for organometallic polymers, and the structure and downfield position support a well-solvated, unassociated environment. 

NMR spectra were recorded on Bruker AC200 spectrometers unless indicated otherwise deuteriated chloroform was used as solvent and tetramethylsi-lane as internal reference. Chemical shifts (8) are given in ppm. The following abbreviations were used to define the multiplicities s, singlet d, doublet t, triplet q, quartet m, multiplet br, broad coupling constants (/) are measured in Hertz (Hz). IR spectra were recorded on a Nicolet Magna-550 FTIR... 

Proton-decoupled 13C-NMR spectra were recorded on a Varian XL-300 operating at 75.4 MHz. Approximately 250 mg of the sample was dissolved in 3 ml of deuterated chloroform. 13C chemical shifts were referenced internally to CDCL (77 ppm). A delay of 200s was used to ensure relaxation of all the carbon nuclei and 1000 transients were collected to assure a good signal-to-noise ratio. 

Infrared spectra were obtained with a Perkin-Elmer 1800 and a Nicolet Magna-IR 750 FTIR spectrophotometer, and the absorption frequencies are reported in wave numbers (cm4). NMR spectra were obtained with BZH-300 and CA-F-300 Bruker FTNMR 300 MHz spectrometers. Chloroform-d was used as solvent, and all chemical shifts are reported in parts per million downfield (positive) of the standard. H-NMR and 13C-NMR chemical shifts are reported relative to internal tetramethylsilane, while 19F-NMR chemical shifts are reported relative to internal fluorotrichloromethane, Rf values were obtained from silica gel thin-layer chromatography developed with a mixture of 1.5 mL methylene chloride and three drops of acetone. The number of hydrate water molecules was calculated from the integration of H-NMR spectra. 

In order to prepare NiPz (4) derivative, H Pz was reacted with Ni(Ac)j.4HjO in the mixture of chloroform and ethanol to obtain NrPz. In the H- NMR spectram of NiPz, chemical shifts assignable to -SCH, C-CH -C, -CH and -CH groups at 4.2,... 

The spin-spin coupling constants for the spectrum of dibenzothiophene in carbon tetrachloride and acetone have been accurately determined by computer analysis and listed. In routine structural studies of derivatives of dibenzothiophene it is usually found that ortho-couplings are close to 8 Hz, meta couplings about 2 Hz and between 0.5 and 1 Hz. In chloroform-dj, H-2 and 3 in dibenzothiophene have the same chemical shift and the spectrum of 1,4-dimethyldibenzothiophene in this solvent also shows H-2,3 as a singlet at 87.03. Apart from the minimal coupling which has been detected between H-1,9 of 0.08 Hz, no interring coupling is observed in dibenzothiophenes. 

The polymer obtained from 9 by y-radiation was soluble in chloroform despite a high crystallinity. The alternating molecular stacking of 9 led to stereoregular polymer formation with a disyndiotactic structure. The racemo and meso structures of the resulting polymers were confirmed by NMR spectroscopy. A comparison of the NMR data of related polymers concludes that the chemical shifts for a series of the polymers are predominantly determined by the meso-racemo structure rather than the diisotactic-disyndiotactic one. 

The 90 MHz H-NMR spectrum of benzoic acid shown in Figure 7 was obtained in deuterated chloroform using a Hitachi R-1900 FT-NMR spectrometer. Chemical shifts were measured relative to tetramethylsilane and assignments for the observed bands are found in Table 4. Due to the relatively low resolution of the 90 MHz NMR spectrometer, the only H-H... 

Table 17.1. C-NMR Chemical Shifts for a Series of 4-Fluoroaniline-Based Model Amic Acids Prepared and Isolated from Chloroform (Isomer Formed in Excess Denoted by )...

The, 3C chemical shifts for quinoxalines have been explained in terms of the inductive and resonance effects of the substituents.265 Resonances at 144.8 and 142.8 <5 in the spectrum of quinoxaline in deutero-chloroform are assigned to carbon atoms 2 and 3 and 9 and 10, respectively. Carbons 5 and 8 resonate at 129.6, and carbons 6 and 7 at 129.4.266... 

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