Group frequencies alcohols

In addition to sp C—H stretching modes there are other stretching vibrations that appear at frequencies above 3000 cm The most important of these is the O—H stretch of alcohols Figure 13 34 shows the IR spectrum of 2 hexanol It contains a broad peak at 3300 cm ascribable to O—H stretching of hydrogen bonded alcohol groups In... 

Figure 4 illustrates the infrared spectrum for a sample of PPE. The absorptions of the peaks at 3.4, 6.9 and 7.3 pm were assigned to C-H stretch and C-H bending frequencies in CH2 and CH3 (33). These absorptions are proportional to the surface density of deposited ethane (16). However, the absorptions at photons near 10 pm are attributable to OH deformations and CO stretchings of alcoholic groups and vibrations of alkyl ketones (22). They also indicate the existence of branches in unsaturated chain (33). 

Useful characteristic group frequency bands often involve coupled vibrations. The spectra of alcohols have a strong band in the region between 1260 and 1000 cm-1, which is usually designated as the C—O stretching band. In the spectrum of methanol this band... 

The group frequency region falls approximately between 4000 to 1400 cm-1, and the absorption bands in it may be assigned to vibration of pairs of two (or sometimes three) atoms. The frequency is characteristic of the masses of the atoms involved and the nature of their bond, ignoring the rest of the molecule. Therefore, IR spectra are useful for determining the presence of functional groups in organic compounds alcohols (—OH), ketones (=CO), amines... 

Table 4.10 OH and Related C—O Group Frequencies for Alcohols and Carboxylic Acids...

The macro group frequencies for 4-chlorobenzyl alcohol are as follows ... 

The acidic product generated in the reaction is assumed to be 4-chlorobenzoic acid. This material also is a para-substituted aromatic compound thus, the spectrum of this compound (Fig. 6.17) possesses a macro frequency train (a), similar to those of the aldehyde and alcohol. In addition, this benzoic acid derivative exhibits an extended aromatic acid macro group frequency train (b).The macro frequencies are as follows ... 

Infrared Analysis. The conversion of a branched-chain aliphatic primary alcohol to an acetate ester results in significant changes in the infrared spectrum of the molecule. These changes are similar to those observed in straight-chain systems. The two macro group frequency trains in the present example are... 

If the macro group frequencies are further constrained to include only those systems in which the chain branching involves the presence of an isopropyl group, two additional bands near 1385 and 1365 cm are required. These peaks, which are present in both the alcohol and the ester, arise from the spatially coupled and split symmetric methyl bending vibrations of the aliphatic backbone. In both isopentyl alcohol and isopentyl acetate, this pair of bands are found at identical locations, 1386 and 1367 cm . ... 

Figure 22. Characteristic group frequencies of alcohols and phenols...

Spectral analysis based on group frequencies and the spectra-structure correlation method is well established in IR and Raman spectroscopy. These methods are also becoming popular in NIR spectroscopy, and recently Weyer and Lo (30) wrote a valuable review article on the relationship between NIR bands and chemical structure. They compared NIR spectra of selected aliphatic hydrocarbons, those of selected aromatics, those of selected alcohols, and so on and discussed detailed spectra-structure correlations in the NIR region. Tables for group frequencies in the NIR region are also available in some NIR books (3,4). 

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