A comparative study of the IR spectra of alkaloids containing piperidine and quinolizidine rings in the 2500–2830 cm−1 region
Summary1. A comparative method of studying the conformational states of alkaloids of the piperidine and quinolizidine series by comparing the intensities of the IR bands in the 2500–2830 cm−1 region in the solid and liquid states has been proposed.2. It has been shown that the process of inversion and other labile conformational transformations affect the number, frequency, and intensity of the vibrational transitions in the “Bohlmann region.”
Correlation between the stereochemistry of quinolizidine alkaloids and their infrared spectra from 2840-2600 CM-1.
Abstract The IR spectra from 2840-2600 cm −1 of a number of sparteine type quinolizidine alkaloids and their selectively α-deuterated derivatives have been examined. It was shown that a single absorption band or band complex arises from the stretching vibrations of one or more axially oriented C α H bonds. The intensity and general complexity of this absorption is roughly proportional to the number of these trans -diaxial α hydrogens and their steric environment. The characteristic absorption in the 2840-2600 cm −1 region has been correlated with different conformations of quinolizidine ring fusions. Steric factors influencing this absorption in sparteine type alkaloids are discussed. An attempt has been made to rationalize the nature of the specific interaction of C α H(a) bonds with the lone electron pair on nitrogen in the compounds investigated.
Description of roughness profiles by separating the random and periodic components
Abstract The probability that it is not possible to obtain a significant description of roughness profiles composed of random and periodic components by using statistical methods is discussed. It is shown that the random and periodic components can be separated by using the frequency spectrum and the autocorrelation function of the profile. The physical significance of the separate components is discussed and it is shown that it is possible to describe a long crested surface by a single profile using these components The method of separating the random and periodic components allows a parametrical description of the roughness profile to be given. It is then possible to use these parameters to calculate a synthetic signal sign with the same basic properties as the measured profile.