R-band

The R band characteristic for aromatic aldehyde groups (aldehyde n TT bands) occurs in the spectrum of A -methylcotarnine (9a) and that of JV-benzoylcotarnine (9c), which are real aldehydes, at 330 m/i in the form of an inflection. Even in alkaline solution the hypothetical amino-aldehyde form of cotarnine can only occur in amounts not detectable by spectroscopic methods. 

The original research described in this paper was conducted with the support of the Natural Environment Research Council and the skilled assistance of S.R. Band and N. Ruttle. I am particularly grateful to B.D. Campbell and J.M.L. Shacklock for permission to reproduce a figure from an unpublished manuscript. 

I—I Negative or pale Staining Q and G Bands I—I Positive R Bands... 

J.H., and O Donnell, D.J. (1985) Determination of framework aluminum content in dealuminated Y-type zeolites a comparison based on unit cell size and wavenumber of i.r. bands. Zeolites, 6, 225-227. 

Niobium(m) and Tantalum(in) Complexes.—The first tantalum(iii) compounds have been reported. TaCl and MeCN react at 100 °C to form the diamagnetic dimer [TaCl3(MeCN)2]2- The compound exhibits five i.r. bands in the 23(X) cm region, suggesting more than one environment for the MeCN groups the structure (44), analogous to that of [WCl3(py)2]2, has been proposed for the... 

The number of such independent terms in a metal hexacarbonyl is 13 (10 if we discard quartic terms containing the distortion of some CO group raised to an odd power), in addition to the three harmonic force and interaction constants. Thus the number of physical quantities exceeds the number of parameters that may, with the available data, be fitted to Eq. (18). There is the further possibihty that the observed frequencies are distorted by interaction with solvent in a way that is not adequately compensated for by Eq. (18). The classical amplitude of a triply excited oscillator is greater than that for one that is only singly excited, and so jostling of solvent and solute molecules, and variability and asymmetry in the solvent sheath, may become important. This may explain the observation that binary and more especially ternary i.r. bands are considerably broader than are fundamentals in the same solvents. 

R-bands—In addition to the high intensity K-bands, all double bond groups such as C C, C N, C 0, C S N N, N 0, N0 0 are responsible for the appearance of absorption bands of very low intensity, in simple compounds at considerably longer wave-lengths than the K-bands (e, <20 in simple and up to a few thousand in more complicated molecules). In the absence of any evidence to the contrary, these R-bands may be considered to correspond to transitions of the same type, since, as far as they are accessible to experimental test, they have been shown to obey the same very characteristic optical rules (effects of substituents, of solvents and of proton addition) [15, 17]. 

The following discussion will be based on the view that the transition responsible for the R-bands originates in the bonding electrons of the double bond. Qualitatively, it involves a charge migration (in phase) towards both atoms of this bond, the perturbation extending into the substituents (of. XV and XVI). There are two possibilities. Only one pair of electrons, e.g. the n electrons, participate. This would correspond to a singlet-triplet transition, forbidden both by spin requirements and a small transition moment. 

R-bands. They also explain their displacements to shorter wave-lengths by all influences which increase the polarity of the absorbing system, since the electron-shifts in the ground state, at least in the substituents, are opposite to the direction of the effective charge migration. (For a more detailed discussion, cf, [24].)... 

In Table 7, data for the B- and K-bands of o-hydroxybenzaldehyde and o-nitrosophenol, for the R-bands of the latter substance and of o-hydroxythiobenzophenone, and for the corresponding bands of them methyl ethers in hexane (or benzene) solution are shown. 

Again, the appreciable electron-shifts towards the hydrogen accepting 0 and S atoms in o-nitrosophenol and o-hydroxythiobenzo-phenone should account for the strong displacements to shorter wavelengths of the R-bands (—785 and —650 A respectively). 

From the geometrical similarity between piperidine and cyclohexane it may be assumed that the N-U vibration causing the dipole change in 94 is parallel to the major axis of rotation (largest moment of inertia /c) and accordingly the Q branch should be strong and the P and R bands, weak (parallel-type band). On the other hand the N-H equatorial bond in 93 has 28% parallel character (N-H bond 1110 to / ), and P, Q, and R bands of... 

---