Spectrochimica Acta最新文献

Infra-red spectra of a series of acetylacetonates XX′Sn(acac)₂ (X, X′ = alkyl, aryl and/or halogen), (CH₃)₂Pb(acac)₂, Cl₂Ti(acac)₂, Cl₂Ge(acac)₂ and Cl₄Sb(acac) have been measured in the region of 4000-400 cm⁻¹. The absorption bands in XX′Sn(acac)₂ are classified into three groups. The bands in the first group decrease in frequency with increasing electron attracting power of substituents X and/or X′ and those in the second group show an opposite behaviour. The bands in the third group are almost independent of the substituents. From the substituent dependence of the frequency, the upper strong band in the region of 1600-1500 cm⁻¹ is assigned to a perturbed CO stretching band and the lower band to a perturbed CC stretching band. The separation of these two bands becomes small as the electron attracting power of substituents increases and in Cl₄Sb(acac), which may be an extreme case, only a single sharp band is observed. The substituent sensitive bands in XX′Sn(acac)₂ in the region of 700-400 cm⁻¹ have been found to correspond to metal sensitive bands of usual metal acetylacetonates M(acac)_n (n = 1, 2, 3 and 4).

The infra-red spectra of aseries of N-monosubstituted amides R · CONH · R′[R or R′ CH₃, C₂H₅, CH(CH₃)₂, C(CH₃)₃] in carbon tetrachloride solution have been recorded in the region 3600 cm⁻¹ −2800 cm⁻¹. The shift in the NH stretching frequency on hydrogen—bonding (Δν  ν_monomeric — ν_associated) has been found to be proportional to the estimated area (B) of the association band, and to the width at half-height (ν_{$\text{1}\text{2}$}) of this band. B was also found to be proportional to the concentration ratio ϱ=$\text{C}{}_{\mathrm{associated}}\text{C}{}_{\mathrm{monomeric}}$

In a series of secondary amides where R  R′  n-C₃H₇ to n-C₆H₁₃ inclusive, Δν, ν_{$\text{1}\text{2}$}, and B were essentially constant.

Infra-red OH stretching spectra of 2-methoxy-1-naphthoic (I), 1-methoxy-2-naphthoic (II) and 3-methoxy-2-naphthoic (III) acids were measured under conditions where dimeric association and solvent—solute hydrogen bonding could be neglected. From these spectra, together with their ultra-violet spectra, the following conclusions were obtained: (i) The intramolecular hydrogen bond in III is the most favourable, while it is absent in I. This result is in accordance with the conclusion reported previously by the present authors, and can be explained in terms of the steric effect caused by the peri-hydrogen. (ii) The enthalpies of the hydrogen bond formation of II and III are 2·32 and 2·46 kcal/mole, respectively. (iii) Comparison of the ultraviolet spectra of these acids with their esters reveals that there is a remarkable hydrogen bond effect on the spectrum of III.

The ultra-violet spectra of methyl 2-hydroxy-1-, 1-hydroxy-2- and 3-hydroxy-2-naphthoates were also determined and discussed from the view point of the pseudo-aromatic nature of the chelate ring formed by the intramolecular hydrogen bond.

Intensity measurements of the CH-stretching vibrations of 40 monosubstituted pyridine derivatives show that also for pyridine derivatives there exists a functional relation between the intensities and the Taft substituent parameters σ_I. The interpretation of these facts leads to conclusions concerning the polarity of the CH bond moments of the investigated pyridine derivatives. We also discussed the influence of the hetero—N—atom on the CH bond moments.

The microwave spectrum of m-C₆¹²H₄F₂ has been measured from 18·0 to 25·0 GHz with wavemeter and frequency standard techniques, using a Stark modulated gas-absorption, microwave spectrometer. The analysis of the spectrum is based on the rigid asymmetric top theory; the rotational constants and the principal moments of inertia were determined and a preliminary structure of the molecule is given. The results are in agreement with the assumed planarity of the molecule and with normal values of bond distances. The rotational constants are: A = 3739·97 ± 0·3 MHz., B = 1734·95 ± 0·1 MHz., C = 1185·48 ± 0·1 MHz. The inertia defect obtained is I_c  I_a  I_b = −0·11 amuA².

The infrared intensities of cis- and trans-dichloroethylene and trichloroethylene were measured in solution in CS₂ and CCl₄. The observed values are in accord with those previously reported for other ethylenes.

It is shown that to a good approximation the CH-stretching vibrations in benzene derivatives are localized in the CH bonds and that the total intensity of a CH-stretching vibration of such a compound is given by the sum of the squares of the derivatives ∂μ|∂R_j: I_CH = $\text{j}\text{́}$($\text{∂μ}\text{∂}\text{R}{}_{\mathrm{j}}$) ∂μ|∂R_j is the change of the molecular dipole moment with respect to a change of the stretching coordinate R_j of the jth CH bond. Experimental data demonstrate the validity of this approximation.

In continuation of our former investigations on the dependence of the CH-stretching vibrations on different substituents we have examined a considerable number of deuterated benzene monoderivatives, para-disubstituted benzene derivatives and 2-, 3- and 4-substituted pyridine derivatives. We have found a relation of general validity between I_CH and the Taft substitution constant σ_I: I_CH = F(σ_I). The interpretation of this result leads to conclusions concerning the effect of substituents on the CH dipole of benzene derivatives.

The experimental conditions for the measurement of absolute infrared intensities of vibrational transitions have been examined using the out-of-plane CH vibration of 1,2,4,5-tetrachlorobenzone. This symmetrical band has been investigated in solution in carbon disulfide. The band was analyzed by the band shape moment analysis. The error in the experimentally determined intensity is estimated to be ±5 percent. It is suggested that this band would be useful as an intensity standard in condensed systems.