A perturbation treatment of the intramolecular coupling in helical molecules is examined. A general classification of characteristic band types resulting from changes in stereoregularity is established. Comparisons are made with previous classifications and experiment.
The infra-red spectra (650-222 cm−1) of nine 2-substituted pyridines, including those of four 2-pyridylamines, have been recorded. Solid compounds have been examined as mulls and as chloroform and/or carbon tetrachloride solutions and pronounced solid state effects were noted in one case. Empirical assignments of the major bands have been attempted and it is concluded that ν6b-α(CCC), ν11-X-sens φ(CC) and ν16a8φ(CC) may be assigned with some certainty even when the molecular complexity is considerable.
The in-plane vibrations of azulene have been computed using different force fields based on the benzene fields of Srawford et al. and of Duinker and Mills. The agreement between the two sets of results and obvious assignments is very satisfactory. An almost complete assignment of azulene is presented based on the calculations and previous experimental data. The results of calculation of the frequencies of per-deutero azulene are given but not discussed.
An assignment of the vibrational spectra for 2-chloro-, 2-bromo- and 2-iodothiophene has been made, using infrared gas-phase data, Raman polarization data, and comparison with spectra of related molecules.
The infra-red spectra of either trivalent cations or rare-earth borates related to the calcite, the aragonite and the vaterite structures have been studied in the 1500-250 cm−1 region.
The infra-red pattern given by the rare-earth borates of the YBO3 type cannot be reconciled with a three-fold co-ordination, but instead points to a four-fold co-ordination of boron, a fact in contradiction with the alleged vaterite structure of these borates.
The low-frequency spectrum is strongly structure-dependent, and is clearly influenced by the co-ordination number of the trivalent cation. The strong band observed in this region may be assigned to a cation—oxygen vibration, or possibly (for the calcite or aragonite-type borates) to a libration of the borate anion. Some significant discrepancies between our results and some data recently published in the literature are found to be related to spurious effects, such as the granulometry of the sample and possibly orientation effects.
Comparison of the spectra of syndiotactic, isotactic and atactic polypropylene illustrates the sensitivity of the infrared spectrum to changes in polymer systems resulting from stereoregularity. The bands are classified according to general types dependent on stereoisomer, degree of coupling due to stereosequence length, and the helical conformation.
Infra-red spectra of the molecule S2N2 were obtained under a variety of conditions. Attempts to obtain Raman spectra were unsuccessful due to its extreme reactivity. The spectral evidence is consistent with a planar ring structure of D2h symmetry, with infra-red fundamentals at 474 (B1u), 663 (B2u) and 795 cm−1 (B3u). The possibility of the molecule being a puckered ring, of C2υ symmetry, cannot, however, be ruled out.
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