Hydroxylic peak

The amount of a particular component in a sample can be monitored by examining the height of a spectral absorption peak The reduction of an aldehyde to an alcohol would show up as a decrease in line intensity for the carbonyl and an increase for the hydroxyl peaks in the spectrum. Changes in the relative importance of different relaxation modes in a polymer can also be followed by the corresponding changes in a mechanical spectrum. 

We therefore studied the effect of temperature and of concentration on the position of the hydroxyl peak in simple alcohols (methanol, ethanol, etc.) in the pure state, and in carbon tetrachloride or chloroform solutions. Some of the results of this work have already been reported [1]. A plot of peak position against concentration gives curves such as that in Fig. la. Interpretation of this type of curve from the N.M.R. data alone is impossible. It is clear that several different species (monomer, dimer, polymers) are contributing their effect, but because of the averaging phenomenon only a single OH peak, representing the weighted mean of all these species, is observed. We have now used infrared spectral data to clarify the situation. A careful examination of the infrared spectrum of all normal aliphatic alcohols... 

Using Fourier Transform Infra Red (FTIR) spectroscopy, the reaction can be monitored. The progress of the reaction also can be followed by studying the reduction of the primary hydroxyl peaks in the mid-infrared spectra. The urethane band with the approximate wave number 1739 will be forming. The NCO band at 2273 will decrease from a maximum and then stabilize as the chain extension proceeds. 

In fact, many other authors12,13,14,15 16,17 have noticed a shift in the free hydroxyl peak maximum as a function of temperature. 

Alcohols Depending on concentration, the hydroxylic peak in alcohols is found between S 0.5 and S 4.0. A change in temperature or solvent will also shift the peak position. 

Rapid exchangeability explains why the hydroxylic peak of ethanol is usually seen as a singlet (Figure 3.38). Under ordinary conditions—exposure to air, light, and water vapor — acidic impurities develop in CDC13 solution and catalyze rapid exchange of... 

The progress of thermal decomposition is illustrated by the series of spectra for chars in Figure 8. The chars were produced by devolatilizing coal PSOC 212 for 80 sec at the indicated temperature. The results are similar to those observed by Brown (16) and Oelert (17). The rapid disappearance of the aliphatic and hydroxyl peaks is apparent. The aromatic peaks remain to high temperature, and the ether peaks are observed to increase in intensity, possibly from the creation of new ether linkages by... 

The temperature may also be measured by the separation between C—H and hydroxyl peaks in liquid methanol or ethylene glycol. 

In a small-scale test behind a safety shield pentaerythritol (mp 260°C) dissolved readily in (Li, K)NOa eutectic (41.2-58.8 mole%, mp 125°C) at 130°C to form a 16% by weight solution. A 10% solution showed no visual evidence of reaction at 200°C. DTA runs made with small samples of 10% pentaerythritol-90% (Li, K)NOa eutectic with heating rates of 10° per minute showed endothermic peaks at 123-125°C, corresponding to melting, and broad exothermic peaks about 375°C attributed to decomposition of the solvent. Essentially, identical DTA s were observed for the pure eutectic solvent. Evidently, a 10% solution of pentaerythritol is reasonably stable in this nitrate melt and therefore we made NMR measurements. A PMR spectrum of pentaerythritol in (Li, K)N03 eutectic at 130°C, taken with a Varian HA-100 NMR spectrometer, was quite analogous to those obtained for pentaerythritol dissolved in thiocyanate or acetate eutectics. Two singlet peaks were observed, which we attribute to the methylene and hydroxyl protons. The hydroxyl peak was far downfield. 

Mixtures of acetic acid and water might be expected to show three peaks, since there are two distinct types of hydroxyl groups in the solutions—one on acetic acid and one on water. In addition, the methyl group on acetic acid should give an absorption peak. In actuality, however, mixtures of these two reagents produce only two peaks. The methyl peak occurs at its normal position in the mixture, but there is only a single hydroxyl peak between the hydroxyl positions of the pure substances. Apparently, exchange of the type... 

IR Spectra. The IR spectra of the pigments dispersed in Nujoi were taken on Beckman 5220 spectrometer. Figure 2 shows the IR spectra of dihydroxy germanium phthalocyanine and that of a typical polymer, (PcGeOCgH C(CH3)2CgH 0). There was no hydroxyl peak detectable in the spectrum of the polymer, while an intense OH peak at 3500 cm was clearly observable for PcGe(OH)2. The absence of OH absorption in the polymers is indicative of at least moderate chain length. 

Figure 34 illustrates the results for a raw and chemically cleaned coal (62) A substantial decrease is observed in the aliphatic peak (2900 cm ) and substantial increases are observed in the carbonyl peak (1700 cm" ), the hydroxyl peak (3500-2400 cm" ) and the ether peak (1250 cm" ) ... 

Only amines tend to produce broad but smaller peaks than hydroxyl peaks around 3300 cm . The number of those peaks can sometimes tell if there is one or two hydrogens attached to that nitrogen atom. 

In the IR spectrum of Unknown 2 (Fig. 2.19) there is a hydroxyl absorption once again centered around 3300 cm , as well as a carbonyl peak at 1705 cm . And. although we cannot always tell what kind of carbonyl is present, when the hydroxyl peak is extremely broad and has a ragged appearance (due to overlap of the C —FI absorptions that extend below it. in contrast to the first spectrum where the hydroxyl was smooth, it is usually safe to assume that this hydroxyl group is attached to the... 

In ethanol, the hydroxyl peak should be split by spin-spin interaction with the methylene protons. However, the high-resolution NMR spectrum shows only a single hydroxyl peak. The lack of apparent spin-spin coupling in this peak is due to the fact that this spectrum was taken on a sample that contained a small amount of water. In the NMR spectrum of pure ethanol, the hydroxyl peak will be a triplet as we expect. However, if a small amount of water is present, a rapid proton-exchange reaction between the —OH proton in ethanol and H30 in the water will occur that has the effect of broadening the three peaks in the —OH triplet so that they coalesce into a single observed peak. 

The similar relation can be found for hydroxyl peak shifts. The equations for used acids are based on work by Drago (5, 10-12). We can obtain relation between shift and heat of conqilexation by following formula ... 

Typically fee concentration of model molecules was about 40 mM, and fee ratio to fee probe acids ranged from 1 2 to 1 5 in carbonyl shift study and 1 1 to 1 3 acid/molecule in hydroxyl peak shift study. The sattples were measured using a liquid cell between two NaCl or KCl windows, and BaF2 in OH shift, equipped wife Teflon spacer. Spectra were analyzed using PE Spectrum 2.0 software. In effort to increase clarity of spectra some were treated wife Fourier Transformation deconvohitioa For two probe acids, SbCls and MesAl quite different procedure was used. Because of precipitation of resin and ketone in contact wife probe instead of liquid cell Perkin-Elma HATR accessory was used to analyze fee precipitate. 

To conq>are results fipom caiboiqi shift and hydroxyl peak diift we used a method tibat utilized hardness of base to determine Drago constants. This mediod has been presented before 14). The mediod is based on assunqition that the hardness, i.e. ratio C/E of bases with similar structure are equal. Thus, we assumed hardness of ester and cycloal hatic epoxy model molecules to be equal hardness of ethyl acetate, C p/E p==0.61, hardness of dicyclohexyl ketone to be equal to diat of acetone, C g/E g=0.72 and hardness of Bisphenol A aM F epoxies to be equal to that of cyclohexane oxide, C g/E g-l.S (17-20), Thus, relation (S) can be used to find Eb ... 

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