H. Bruce Friedrich

Infrared Spectra of Charge‐Transfer Complexes. VI. Theory

The general theory of molecular vibrational transition intensities is discussed with emphasis on electronic reorientation contributions to the intensities. The wavefunctions used by Mulliken to represent the electronic states of donor—acceptor complexes are written to include an explicit dependence on the vibrational coordinates. These functions and the general theory are applied to the intensities of halogen vibrations in donor—acceptor complexes. Specific application to actual complexes requires the estimation of the derivative of the vertical electron affinity of the halogen molecule with respect to its internuclear distance, the electronic transition moment of the charge‐transfer band, the coefficients in the donor—acceptor ground‐state wavefunctions and the difference between the energies of the dative‐ and no‐bond states. Evaluation of each of these parameters is discussed for a number of complexes of halogens and relationships between the wavefunction coefficients and the infrared frequency shifts ...

Absolute Infrared Intensities in Some Crystalline Hydrogen Halides

Absolute intensities of the fundamental vibrational bands of HCl and HBr have been measured in the absorption spectrum of crystalline films. The path length has been determined from the interference fringes of the transmitted light as the film is deposited on a window, following the technique of Hollenberg and Dows. The measured integrated molar absorption coefficients B are 24 000±3000 and 17 600±1200 darks (cm—1cm2/mM), respectively, for HCl and HBr. These values are larger than the gas phase intensities by factors of 6 and 13, respectively. Such large intensification of an X—H stretching vibration is consistent with the large frequency shift and is characteristic of hydrogen‐bonded crystals. The results are compared with those from other hydrogen‐bonded systems. Furthermore, the high intensities are consistent with those required by Hornig and Hiebert using the transition dipole—transition dipole model to explain the observed intermolecular force constants. However, it is likely that other terms contri...

Combinations of Orthogonal Spectra to Estimate Component Spectra in Multicomponent Mixtures

A factor analysis of a set of spectra of multicomponent mixtures yields n orthogonal spectra where n is the number of components in the mixtures. Combinations of these orthogonal spectra, done so as to eliminate the contributions to the spectra from one of the components, yield a set of n – 1 linearly independent abstract spectra. Repetition of this process is used to estimate the spectrum of each of the components without identifying the range of the n-dimensional vector space in which the solution must fall. Several techniques for estimating the appropriate combinations of orthogonal spectra are compared.

Infrared Spectra of Charge‐Transfer Complexes. VII. The Solid Benzene—Bromine Complex

The infrared spectrum of the solid benzene—Br2 complex has been measured to give the changes in frequency and an estimate of the changes in intensity from the pure benzene and pure Br2 crystals. The complex was usually prepared by condensing a 1:1 mixture of benzene and bromine vapor onto a cold plate, but other techniques were also tried, and partial studies are reported. These spectra show definitely that neither the benzene nor bromine molecules in our samples are located on a site possessing a center of symmetry. From the analysis of the spectrum of the complexed benzene, a site symmetry of C3v is deduced. This apparent contradiction of the results of the x‐ray studies of Stromme and Hassel is discussed and reconciled. The frequency shifts and intensity changes on complex formation are discussed in some detail.

Absolute Infrared Intensities of the Fundamental Absorption Bands in Solid Cyanogen Halides

Absolute absorption intensities of the three infrared‐active fundamental vibrations of each of the cyanogen halides—CICN, BrCN, and ICN—have been measured for crystalline samples, using experimental techniques developed by Hollenberg and Dows. Comparison between integrated intensities obtained with “drawn in” backgrounds and those obtained after integrating the absorption coefficient, κ, obtained from the measured transmittance by a Kramers–Kronig method, shows that the results agree within their estimated experimental uncertainty. The intensities of the stretching fundamentals in the solid phase differ drastically from those in the gas phase, e.g., ν1 for ClCN goes from an estimated 900 darks in the gas phase to 0 in the solid, ν3 increases by a factor of 2 from gas to solid for ClCN, and by a factor of about 4 for BrCN. However, the solid phase intensities of ν2, the bending motion perpendicular to the molecular chains in the solid, are only slightly larger than the gas phase values, indicating that the...

A facile route to tetrafluoroallene

Abstract Tetrafluoroallene has been prepared in 72%–75% yield by metallation of either 2-hydropentafluoropropene or 2-bromopentafluoropropene with t-butyllithium followed by thermal elimination of lithium fluoride from the 2-lithiopentafluoropropene. The 2-bromopentafluoropropene route gives the allene free of isobutane.

Absolute Absorption Intensities of the Librational Modes of ClCN and BrCN

The absolute absorption intensities of the two infrared‐active librational modes in crystalline ClCN and BrCN have been measured. The sums of the intensities of the two modes were 750 ± 90 and 800 ± 140 cm mM−1 for ClCN and BrCN, respectively. A dipolar coupling model was used to compute the expected intensities and the contributions of dipolar interactions to the frequencies of these lattice modes. The evaluation of the lattice sums in the direct or reciprocal lattice is discussed. The calculated intensities were 970 and 835 cm mM−1 for ClCN and BrCN, respectively.

Odd Moments of the Cross-Correlation Function for Library Searching of Infrared Spectra

The odd moments of the autocorrelation function are zero, and the moments of the cross-correlation function for an unknown spectrum with a library entry have been used here to select the best fits. The use of the first moment or average wavenumber in six separate spectral ranges requires only 12 values per library entry, and 24 values are required per library entry if twelve separate ranges are used. The odd moment methods were found to yield results for searches with both library and experimental spectra that were comparable to correlation coefficients in selection of the proper chemical class for the unknown spectra and in making of the proper identification.

Infrared spectroscopic determination of methyl-chlorosilanes from the direct process reaction

Abstract Infrared spectroscopy was used to determine the distribution of products from a flow reactor. Gas-phase methylchlorosilanes, which were formed in the copper-catalyzed reaction of methyl chloride with silicon, flowed through a gas cell used for the infrared measurements. The silanes could be determined simultaneously at pressures of 1–100 Torr in the presence of methyl chloride at atmospheric pressure. The calculated results were similar to those obtained by standard gas chromatographic techniques; however, the infrared method required only 15 s for data collection.

The vibrational spectrum of tetrafluoropropyne

Abstract The i.r. spectrum of gaseous tetrafluoropropyne has been measured from 4000 to 100 cm −1 , and all of the observed bands have been assigned. The e mode frequencies of the CF 3 group are similar to those of other CF 3 CCX species, and even though the a 1 modes are less regular, the variations can be explained without changes in force constants other than those involving the CX bond. Several bands, particularly ν 1 and combinations with ν 1 , show pronounced sequence structure due to excited levels of ν 10 , the CCC skeletal bend.