Doublet methylene

The spectrum of styrene in toluene was compared with that in toluene containing an equimolar quantity of Zr (benzyl) 4 at 0.06 M using a sweep of 2500 Hz. The methylene doublets of styrene were in identical positions (1115 and 1230 Hz) in these spectra. Experiment (b) (Table XIX) was repeated at — 60°C using 250-Hz expansion on a 100-MHz spectrometer. The benzyl resonance was observed to shift approximately 4 Hz (relative to toluene) upheld. The lack of splitting in the latter indicates equilibrium (if any occurs) is very rapid. Finally, the effect of temperature on the systems Zr (benzyl) 4 in styrene and Zr (benzyl) 4 toluene were examined and the results are given in Table XX. They show that no specific interaction of styrene with Zr (benzyl) 4 occurs. The interaction of toluene would probably be of the type (XXIV) whereas styrene would interact similarly or in a manner shown in (XXV), both interactions would affect the environment of the benzyl protons in Zr (benzyl) 4 if they occurred to any significant... 

The principal saturated hydrocarbon functional groups of concern are methyl, methylene and methyne (—CH3, —CH2—, = CH—). The spectra of typical hydrocarbon mixtures (for example as in gas oil and gasoline) are dominated by two pairs of strong bands in the first overtone and combination regions (5900-5500 cm-1 and 4350-4250 cm-1). These are predominantly methylene (—CH2—). The methyl end groups typically show up as a weaker higher-frequency shoulder to these methylene doublets. 

The absorption of the single methine proton in the presence of methyl and methylenes is generally too small to be observed and is little mentioned in the literature. In the mid-infrared, the fundamental peak is near 2900 cm , between the methyl and methylene doublets. This would suggest that its first overtone was also in the envelope of small peaks in the 5882-5555-cm- (1700-1800-nm) region. 

Most of the methyl and methylene C—H stretching modes that are good group frequencies in the linear alkanes transfer directly to branched alkanes with little change in wavenumber value. The relative intensity of the C H stretch methyl doublet compared to the methylene doublet, however, often will be quite different from the linear chain isomer. 

NMR is the method of choice for determining the ratio of EO units to PO units since the analysis is simple to perform, does not require calibration, and is applicable over a wide range of EO-PO ratios. The spectrum contains only two resonances a doublet due to the methylene groups of the PO units, and a composite band, which is due to the CH2O groups of the PO and EO... 

When methylene protons at 1.82 p.p.m. are irradiated, each signal at 3.15 and 2.92 p.p.m. splits into a doublet with a coupling constant, 1.6 c.p.s., and a doublet with 9.6 c.p.s., respectively. Therefore, the assignment of the signals at 3.15 and 2.92 p.p.m. to C-2 and C-4 protons, is clearly established (C in Figure 4). The coupling constants again confirmed the axial- equatorial or equatorial-equatorial relation between C-l and C-2 protons and axial-axial relation between C-4 and C-5 protons. 

Reduction of epoxide 21 with lithium aluminium hydride gave a crystalline branched-chain methyl heptoside derivative 24. The NMR spectra of compounds 21 and 24 were very similar. In the spectrum of compound 24 the disappearance of the two sharp doublets at r 6.80 and 7.45 (2 protons) and the appearance of a singlet at r 8.65 (3 protons) is consistent with the reductive cleavage of epoxide 21 to give a substance 24 with a methyl substituent. The multiplet at r 7.40-8.50 ( 5 protons ) was assigned to the four protons of the two methylene groups and the hydroxylic proton. 

The presence of methylenic bands shifted at higher frequency in the very early stages of the polymerization reaction has also been reported by Nishimura and Thomas [114]. A few years later, Spoto et al. [30,77] reported an ethylene polymerization study on a Cr/silicalite, the aluminum-free ZSM-5 molecular sieve. This system is characterized by localized nests of hydroxyls [26,27,115], which can act as grafting centers for chromium ions, thus showing a definite propensity for the formation of mononuclear chromium species. In these samples two types of chromium are present those located in the internal nests and those located on the external surface. Besides the doublet at 2920-2850 cm two additional broad bands at 2931 and 2860 cm are observed. Even in this favorable case no evidence of CH3 groups was obtained [30,77]. The first doublet is assigned to the CH2 stretching mode of the chains formed on the external surface of the zeolite. The bands at 2931 and... 

We can now use a homodecoupling experiment to show that in the methyl signal (triplet, with each line split into a doublet) at 1.33 ppm, the distances between lines 1 and 3, 2 and 4, 3 and 5 or 4 and 6 are equal to (3JH-c-c-h) we irradiate the methylene protons and observe the methyl protons. The result of this experiment is shown in Fig. 3. 

Organic compounds contain four types of carbon atom methyl, methylene, methine and quaternary. And so if we simply record the spectrum as we would a proton spectrum, the result will be a series of quartets, triplets, doublets and singlets, each associated with a carbon-proton one-bond coupling constant of between 125 and 250 Hz. If we are dealing with a complex molecule, these multiplets will overlap and give us spectra which are almost impossible to analyse. In addition, coupling interactions over two or more bonds complicate the picture still further. 

The upper signal consists of a doublet of doublets, with two coupling constants 39.7 Hz and 5.2 Hz. The first is the one-bond coupling constant dco while the second is 3JPOcc> which we have already observed in the normal carbon-13 spectrum. The methylene signal would look similar if we expanded it. 

The chemical shift of the amine nitrogen is 55 ppm and shows a clear 3-bond correlation to the aromatic proton giving a fine doublet at 7.49 ppm. There is also a strong, and in this case, very useful, 1-bond correlation to this nitrogen from the amine proton itself. Note that whether or not you see 1-bond correlations depends largely on how broad the -NH signal is in the proton domain. The sharper the -NH, the more likely you are to see them. As with 13C HMBC, 2-bond correlations can sometimes be quite weak and that is so in this case as there is no obvious correlation to be seen from the methylene protons adjacent to the amine. 

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