Group frequencies isopropyl

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 . ... 

In order to describe group frequencies in the following sections, the structural unit which appears to be responsible for the band will be utilized. Such groups as CH3, CH2, CH, OH, or NH, or rings such as cyclopropane, benzene, etc., can be described as having characteristic group frequencies, as can also structural units such as the isopropyl and r-butyl groups. Finally, combinations of structural... 

IR Spectroscopy. Samples for IR spectroscopy were prepared by pressing 100-mg KBr pellets containing 1 mg of sample. Samples were run both on a Perkin-Elmer model 167 dispersive (grating) instrument and on a Perkin-Elmer model 1750 Fourier transform diffractometer-model 7300 laboratory computer system. Only the latter instrument afforded the resolution needed to identify the skeletal frequencies of isopropyl groups. 

Extensive theoretical and empirical work (17) has shown that the isopropyl group is identifiable by (1) split symmetrical carbon-hydrogen deformations at 1382.5 2.5 and 1367.5 2.5 cm"1 and (2) by two skeletal vibrations. One of these vibrations occurs at a remarkably constant frequency of 1168.5 1.5 cm"1, whereas the frequency of the other vibration decreases as a function of the molecular weight (MW) of the rest of the molecule, from 1170 cm"1 for MW 15 (methyl group) to 1142 cm"1 for MW 99 (heptyl group). For an attached moiety of MW 259, as in abietic acid, the band whose frequency depends on the molecular weight of the rest of the molecule is found at still lower wavenumbers. 

Absorption due to various kinds of carbon-Indrogen bending, which occurs at lower frequencies, can al o be characteristic of structure. Methyl and methylene groups absorb at about 1430 1470 cm for methyl, there is another band, (juitc chaiacteristic, at 1375 cm". The isopropyl split is characteristic a doublet, with equal intensity of the two peaks, at 1370 and 1385 cm (confirmed by a band at 1170 cm ) /cr/-ButyI gives an unsymmetrical doublet 1370 cm strong) and 1395 cm" moderate). 

Obviously the deshielded CH3 singlet at 5 2.27 represents one of the substituents. The six-proton doublet at lowest frequency in the H spectrum and the deshielded one-proton septet spell out an isopropyl group. Thus we have the following pieces on an aromatic ring a hydroxylic proton, a CH3 group, and an isopropyl group. 

Values from Tables 2.14 and A.l of Reference 34, except those for a and b groups, have been recomputed using experimental vibrational frequencies reported by Pacansky and Scharder and by Pacansky and Coufal for ethyl and isopropyl, respectively. Note that CpS, for d, e,f and g are assumed equal to those for P, S, T and Q, respectively. 

The spectra of methyl isopropyl ketone and mesityl oxide are shown in Figures 25.14 and 25.31. The spectrum of camphor, shown in Figure 25.32, has a carbonyl group that has been shifted to a higher frequency because of ring strain (1745 cm ). 

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