Group frequencies aromatic

Arrhenius parameters The pre-exponential factor A (also called the frequency factor) and the activation energy Ea. See also Arrhenius equation. aryl group An aromatic group. Example —C6H5, phenyl. 

The structure of pontevedrine [31] has been revised since the 13C NMR spectrum (CDC13) shows the presence of the C(4) and C(5) carbonyl groups (S 48 and 55). (35) The H NMR spectrum of cepharadione B is shown in [32]. The highest frequency aromatic proton... 

In the spectrum of the cancentrine model compound [171] one of the methoxyl group of protons absorbs at low frequency (5 3-38) compared with absorption for the other methoxyl protons at <5 3 85, 3-85, and 3 90. This low frequency signal was assigned to the 7-methoxyl protons. In the hydrogenated derivative the lowest frequency methoxyl proton absorption is at <5 3-65. The low frequency aromatic proton absorption ((56-59) in [171] was assigned to the 8-proton. Both low frequency shifts are attributed to the shielding effects of ring c. (127)... 

Extensive correlation tables and discussions of characteristic group frequencies can be found in specialized references. As one example, consider the band patterns of toluene, and of o-, m-, and p-xylene, which appear in the frequency range 2000 to 1650 cm" (Fig. 2). These band patterns are due to changes in the dipole moment accompanying changes in vibrational modes of the aromatic ring and are surprisingly similar to those for monosubstituted and other o-, m-, and p-disubstituted benzenes. 

Monocyclic aromatic compounds exhibit a strong characteristic band at a group frequency near 400 cm, this is the shown in Fig. 8.7. 

Fig. 8.7 The form of both components of the, group frequency mode at ca 400 cm in aromatic compounds ( , atoms at nodes the larger the symbol the greater the atomic displacement).

Because of the participation of the enamine double bond in the resonance of the aromatic ring of heteroaromatic /J-enamino esters, the group frequency character of the individual bands is low. Thus the El band is essentially vc=Q. Similarly, jS-enamino nitriles do not exhibit coupled vibrations since the nitrile absorption does not participate.24,61... 

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