Infrared Absorption Spectra of Methylenedioxy and Aryl Ether Groups

Abstract

Methylenedioxy, methoxy, and ethoxy groups attached to the aromatic nucleus exhibit 12, 10, and nine major bands associated with these respective groups. Most of them are common to all three groups. The analytical value of the bands for the detection of the groups is discussed. Followingthe original observation by one of the authors (9, 12) that compounds containing methylenedioxy groups exhibit characteristic maxima at about 1040 to 1020 and 943 to 935 cm.-1 in their infrared spectra, a more detailed examination of the spectrum of this group has been made on 100 compounds. The ability to recognize this group by infrared spectroscopy would be of value because the chemical test for this group sometimes fails through an intense coloration produced by some other part of the molecule {6). For comparison, an examination was made on a number of analogous odimethoxy compounds and other methoxy compounds.Spectra were also studied for a limited number of aromatic ethoxy compounds. EXPERIMENTALInfrared absorption spectra from 5000 to 700 cm.-1 were obtained with either a Beckman Model IR-2 or Perkin-Elmer Model 21 spectrophotometer, both equipped with sodium chloride optics.Measurements in the 3000-cm. -1 region were obtained with the former instrument equipped with a lithium fluoride prism or with a Beckman Model IR-3 spectrophotometer equipped with sodium chloride optics. The solvent notations are given in Table I. METHYLENEDIOXY COMPOUNDSThe spectrum of liquid methylenedioxybenzene, determined with a sodium chloride prism in the region from 3330 to 700 cm.-1 and with a lithium fluoride prism in the region from 5000 to 2500 cm.-1, and that of veratrole are illustrated in Figure 1. From a comparison of these spectra and those of 99 other methylenedioxy compounds (Table I) it may be concluded that the methylenedioxy group attached to the aromatic ring exhibits 12 major bands associated with this group-viz., very strong bands at about 1480, 1250, 1040, and 926 cm.-1; strong bands at about 3010, 2960, 2910, 2780, 1360, and 1130 cm.-1; a medium band at about 1400 cm.-1; and a weak band at about 719 cm.-1The 3300to 2500-Cm.-1 Region. The methylene fragment of the methylenedioxy group would be expected to give rise to a doublet due to resonance interaction between the two C-H bonds, not far removed from that of a normal C-CH2-C group, the members of which occur at 2924 and 2857 cm.-1 (4). Two bands which occur in the region from 3000 to 2700 cm.-1 are assigned to this mode of vibration. The strong band at 2778 cm.-1 in the methylenedioxybenzene spectrum, which occurs in all other methylenedioxy compounds within the range from 2801 to 2770 cm.-1, is considered to be the upper band of this doublet. When compounds are measured in the liquid state, in carbon tetrachloride solution, or in potassium bromide, this is a very sharp band; it is replaced by a broad band at 2817 to 2770 cm."1" in hexachlorobutadiene mulls. It occurs beyond the normal range of C-H stretching vibrations and therefore is diagnostic for the methylenedioxy group.

TGA-FTIR Analysis of Torrefaction of Lignocellulosic Components (cellulose, xylan, lignin) in Isothermal Conditions over a Wide Range of Time Durations

“…Most studies assign this peak and the peak at 1131 cm -1 in LS to aromatic C-H in-plane deformation in S units in hardwood and G units in softwood, respectively. However, some investigators have proposed that these absorptions may be due to some other ether-type linkages (Briggs et al 1957;Hergert 1960). This study suggests that both types of vibrations contribute to this peak.…”

“…Correspondingly, the decline of other characteristic phenolic absorptions at 1369 (Nada et al 1998) and 1327 cm -1 (associated with ortho methoxy) (Bermello et al 2002) are evidence of the decomposition of phenolic groups. Nevertheless, assignments of the peaks at 1369 and 1327 cm -1 was difficult in that the former was considered an aliphatic C-H stretch in CH3 but not in methoxy (Faix 1991), while the latter was assigned to C-H bending of the methyl group in methoxy (Briggs et al 1957). Because the intensity of the peak at 1369 cm -1 decreased remarkably and the peak at 1327 cm -1 nearly disappeared after treatment, the peak at 1369 cm -1 was attributed to phenolic OH combined with aliphatic C-H deformation vibrations, and the peak at 1327 cm -1 was attributed to C-H bending of the methyl group in methoxy.…”

“…With the decomposition of the Caryl-O-CH3 group, the peak at 1215 cm -1 shifted to a lower wavenumber. In addition, the intensity of the asymmetric C-O-C stretching peak in aryl-alkyl ether at 1264 cm -1 (Briggs et al 1957;Kotilainen et al 2000) sharply decreased because of the poor thermal stability of the aryl-ether bonds, which undergo cleavage at low temperatures. Thus, the absorption intensities of all side groups in LS, including methoxy, aryl-alkyl ether, and phenolic OH, suggest that decomposition occurred during torrefaction at 220 °C.…”

Bio‐based benzoxazines based on sesamol: Synthesis and properties

“…For S‐sa, the characteristic stretching vibration of (COC) and the asymmetric and symmetric stretching of (CNC) in oxazine ring were found at 1251, 1194, and 1056 cm −1 in Figure S1. In addition, the peaks at ~928 cm −1 suggested the presence of the benzene ring of all monomers, which supported the successful synthesis of benzoxazine monomers. Similarly, the peaks at 2928 and 2848 cm −1 were attributed to the stretching of methylene groups in the benzoxazine ring.…”

Improvement of dispersion of carbon nanotubes in epoxy resin through pyrogallol functionalization

“…The band at 1,040 cm −1 is due to the CO stretching vibration of alcoholic hydroxyl groups, and the band around 1,180 cm −1 is assigned to the stretching vibration of ester. The CO stretching vibration appeared around 1,735 cm −1 , ArOC asymmetric stretching vibration of alkyl aryl ether appeared around 1,240 cm −1 . The band at 1,507 cm −1 is ascribed to aromatic ring skeleton stretching.…”