Halogen group frequencies

Infrared spectroscopy is an excellent tool in iminoborane chemistry, which readily permits, to distinguish between iminoboranes and nitrile-borane adducts and to identify monomeric and dimeric forms of iminoboranes. This event is due to the fact that the i>CN of CN multiple bonds absorbs outside the fingerprint region and can be considered to be a valuable group frequency even when mixed with other vibrational modes. In some cases other vibrations like NH, BH, B-halogen or B-S stretching modes are helpful for determining the structure of iminoboranes. 

The vibrational spectra of nitrogen oxides and phosphorus compoundshave been reviewed. Figure 11-21 shows a group frequency chart based on these reviews. Appendix VI also gives group frequency chart for KPH), i (PO), and f(PX) (X a halogen). 

Compounds containing P—C Bonds. Vibrational data for CFgPXg, X = halogen or hydrogen, have been assigned on the basis of symmetry but there is considerable mixing of the internal co-ordinates of vibration, and simple group-frequency correlations cannot be made for all bands. 

The presence of a chlorine atom adjacent to the double bond does not appear to shift or obscure the group frequencies of the CH3, CH2, and =CH2 vibrations in the 1500-1350 cm region. In some instances enhancement of band intensity occurs when halogens are present in the molecule. 

Halogens in the ring do not give bands interfering with the assignments of CH3 and CH2 group frequencies. 

I. Except for fluorine, the halogens do not have good group frequencies, and the uses of the latter are limited. It is seldom possible to tell from the IR or Raman spectrum that a halogen is present. The Beilstein test for halogens is very useful in assisting assignments of the C—X vibrations. 

Chapter 9 is concerned with functional groups that may contain —N=0 bonds or Si, P, S or the halogen atoms. With the exception of the X—H stretches derived from these elements and the nitroso (—N=0) and nitrite groups (—O—N=0), the large majority of the group frequencies associated with these elements fall below 1500 cm in the fingerprint region of the spectrum (I). 

Depolarization data on trimethylphosphine oxide are now available and the relationship between the symmetric and asymmetric POP vibrations has been equated for diphosphates, and some halogen and metal salt derivatives. The polarization of a carbonyl group produced by its conjugation with an ylide causes a large decrease in vco- This shift to lower frequency is increased further when a double bond is interposed, thus increasing the extent of conjugation. -... 

Buchmeiser and Nuyken [20], Weberskirch [21] and co-workers, examined the hydroformylation of 1-octene with a series of compounds of the formula [RhX(COD)(NHC)] (Fig. 9.1). The choice of halogen does not affect the reactivity, implying an active catalyst of the general formula [RhH(CO)3(NHC)]. Also, significant differences were observed in the initial TOF between catalysts (8,9) and (10,11) bearing iV- Pr and iV-Mes groups, respectively. Complex 11 exhibited a TOF of 1 480 h , whereas under identical conditions, 9 only turned over at a frequency of... 

In the IR-spectra of 4-haloalkyl-3-imidazoline-3-oxides there are two bands Vc=n due to the two conformers A and B (Fig. 2.12) (367, 389). Conformation B corresponds to the form with the lower frequency band Vc=n (Avc=n 30 cm-1), where the halogen atom is located in the plain of the C=N+-0-group in anti -position to the double bond. Conformation A corresponds to the... 

Moreover, the increase is most marked for those frequencies that are localised in the CO groups trans to each other, rather than for these trans to halogen in the notation of Figure 2, k% is more affected than k. ... 

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