Substituent vibrations

In general, substituent frequencies in azoles are consistent with those characteristic of the same substituents in other classes of compounds. Some characteristic trends are found, and these have been used to measure electronic effects. Thus, for example, the frequencies of v(C = 0) in 3-, 4- and 5-alkoxycarbonylisoxazoles (cfi 129) are respectively 9-12, 2-8 and 17-18 cm higher than those of the corresponding alkyl benzoates, indicating the following order of electron donor power phenyl 4- 3- 5-position of isoxazole. Similar work has been reported for other ring systems and substituents (63PMH(2)l6l). 

Structure of Five-membered Rings with Two or More Heteroatoms 

If the compound does not contain an amino group and the two bands are derived from two separate NH groups, there should be no new band between the original two in the partially deuterated derivative. The method was applied to aminoisoxazoles (61 T( ] 2)51). 

In Table 29 the u(C=0) and other characteristic bands are given for some saturated five-membered heterocycles, and compared with the corresponding absorption frequencies for cyclopentanone. Adjacent NH groups and sulfur atoms have the expected bathochromic effect on r (C=0), whereas an adjacent oxygen atom acts in the reverse direction. The CHa vibrations of cyclopentanone are repeated to a considerable extent in the heterocyclic analogs. 

Boiling points are given at atmospheric pressure to facilitate comparison those reported at other than atmospheric pressure were converted using a nomogram (57MI40101 . ° A dash indicates that the compound is unstable, unknown, or the data are not readily available. 

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Substituent vibrations, mostly v C=0 bands in acetyl derivatives, have also been reported.40,43-46 The location of a carbomethoxy group in the vicinity of the nitrogen (i.e., position 9) in compound 16b has been suggested on the basis of the infrared spectra the... 

Stichtemath, A., R. Schweitzer-Stenner, W. Dreybrodt, R.S.W. Mak, X-Y. Li, L.D. Sparks, J.A. Shelnutt, C.J. Medforth, and K.M. Smith (1993). Macrocycle and substituent vibrational modes of nonplanar nickel(II) octaethyltetraphenylporphyrin from its resonance Raman, near-infrared-excited FT Raman, and FT-IR spectra and deuterium isotope shifts. J. Phys. Chem. 97, 3701. 

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