Methyl group, proton magnetic resonance

Suggestions that PIB may have structure (II) as opposed to structure (I) have been refuted by infra-red studies. These show clearly the split methyl absorption at 7-2 and 7 3 /u.m, characteristic of a gem-dimethyl group. Proton magnetic resonance spectra also indicate a CH3/CH2 proton ratio of about 3, as would be expected from structure (I). 

The H-NMR spectrum of 2 in CDCI3 (Figure 1) exhibits broad unresolved resonances in the aromatic region similar to those found in the monomer. Broad signals with lack of resolution are consistent with magnetic non-equivalence of the methyl group protons resulting from a mixture of triad tacticities. 

In the 1960s, after Kennedy and Thomas [25] had established the isomerisation polymerisation of 3-methylbutene-l, this became a popular subject. From Krentsel s group in the USSR and Aso s in Japan there came several claims to have obtained polymers of unconventional structure from various substituted styrenes by CP. They all had in common that an alleged hydride ion shift in the carbenium ion produced a propagating ion different from that which would result from the cationation of the C C of the monomer and therefore a polymer of unconventional structure the full references are in our papers. The monomers concerned are the 2-methyl-, 2-isopropyl-, 4-methyl-, 4-isopropyl-styrenes. The alleged evidence consisted of IR and proton magnetic resonance (PMR) spectra, and the hypothetical reaction scheme which the spectra were claimed to support can be exemplified thus ... 

It has also been possible to confirm the presence of the reduction product of a Schiff base on the polymer by proton magnetic resonance. For this purpose we have used unmodified poly(ethylenimine), since it too catalyzes the decarboxylation of oxalacetate to its product, pyruvate. Unmodified polyethylenimine was mixed with oxalacetate-4-ethyl ester. One-half of this solution was treated with NaBH4 the second half was exposed to a similar environment but no NaBH4 was added. The borohydride-treated polymer exhibited a strong triplet in the nmr spectrum centered at 3.4 ppm upfield from the HOD resonance. This new feature would be expected from the terminal methyl protons of the oxalacetate ester attached to the polymer. Only a very weak triplet was found in the control sample not treated with borohydride. These observations are strong evidence for the formation of Schiff bases with the polymer primary amine groups. Evidently the mechanistic pathway for decarboxylation by the polymer catalyst is similar to that used enzymatically. 

The boron cation is stable in acidic aqueous solution, somewhat less stable in water, but decomposes in alkaline solution. The proton magnetic resonance spectrum in D20 relative to external TMS shows three bands —8.60 (broad), - —8.19 (doublet, J = 7 Hz.), and —2.85 (singlet), with the expected intensities corresponding to the a- and /6-ring hydrogen atoms and the methyl group, respectively. The bromide is very soluble in cold water and hot ethanol but insoluble in acetone. The hexafluorophosphate is slightly soluble in cold water but very insoluble in acetone. 

Support for the existence of N —Np isomerism in 2 1 metal complexes of o,o -dihydroxydiaryl-azobenzenes has been provided by the application of proton magnetic resonance to the investigation of diamagnetic 2 1 cobalt(III) complexes. A systematic study was carried out of the chemical shifts of the methyl group proton signals in two series of related azomethines on conversion to their 2 1 cobalt(III) complexes. Cobalt complex formation by the first series (98—100) can be regarded as akin to coordination (101-103) in the analogous azo series whilst cobalt complex formation by the second series (104—106) corresponds to Np coordination (107-109) in... 

Fig. 6. Proton magnetic resonance spectrum of methyl groups of methanol in a Co(II)—thiocyanate—methanol solution at —90°C (the field increases from left to right). Peak a, Co(CHjOH)5 peak b, cis-Co(CH30H)sNCS peak c, trans-ColCHsOHls NCS. Peaks d, e and f, g are the respective first and second side bands of the bulk methyl and hydroxy resonances. (From Vriesenga [134], by courtesy of The American Chemical Society.)...

The types of free hydroxyl groups present were determined for several acetals of sedoheptulosan by measuring the proton magnetic resonance spectrum of the compound in dry methyl sulfoxide-dg and observing the multiplicity of the signal caused by the hydroxyl protons. The p.m.r. spectrum of 2,7-anhydro-4,5-0-isopropylidene-jS-D-flltro-heptulopyranose (74) ( isopropylidene-sedoheptulosan ) shows a doublet (/ = 7 Hz) at r 4.90 and a triplet (J = 6.5 Hz) at t 5.33 ... 

R. D. Guthrie and J. Honeyman, Periodate oxidation. I. Structure and some reactions of periodate-oxidised methyl 4,6-O-benzylidene-a-D-glucoside, J. Chem. Soc., (1959) 2441-2448. A. S. Perlin, Hydroxyl proton magnetic resonance spectra in relation to ring size, substituent groups, and mutarotation of carbohydrates. Can J. Chem, 44 (1966) 539-550. 

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