Vibrational spectrum, ab initio calculations, conformational stabilities and assignment of fundamentals of 1,2-dibromopropane.

The mid and far infrared and the Raman spectrum of 1,2-dibromopropane is reported in solid, liquid and gas. Several bands reported by earlier workers are not present in the spectrum of the purified material. Ab initio calculations of optimized geometry, energy, dipole moment, molar volume, vibrational spectrum and normal coordinate calculation were performed using the density functional B3LYP/6-311++g(3df,2pd), and the results used to assist a complete assignment of the 81 fundamental modes of vibrations of the three conformers of 1,2-dibromopropane. Relative energies found conformer A the lowest with G and G' at 815.6 and 871.4 cm(-1) higher. The temperature dependence of the Raman spectrum of the liquid was investigated in the CCC bending region and the relative energies determined. It was found that the G' and G conformers lie 236+/-11 and 327+/-11 cm(-1), respectively above the A conformer, leading to the room temperature composition of the liquid as A, 65+/-1; G', 21+/-1; G, 14+/-1%. It is apparent that the calculated highest energy conformer G' is stabilized more than the G conformer in the liquid. The G' conformer has the lowest molar volume effectively changing the interaction distance between conformers in the liquid, and enhancing the effect of its dipole moment.

Rotational spectra and conformational analysis of diethylsilane and diethyldifluorosilane.

The rotational spectra belonging to the (28)Si isotopologue for three conformers of diethyldifluorosilane (Et(2)SiF(2)) and three conformers of diethylsilane (Et(2)SiH(2)) have been measured between 4 and 17 GHz by using pulsed-jet Fourier-transform microwave spectroscopy. Rotational spectra for the gauche-gauche, trans-trans, and trans-gauche conformers were identified for both molecules, while the significantly higher energy gauche-gauche' conformer was not observed. Ab initio calculations at the MP2(Full)/6-311+G(2d,2p) and MP2(Full)/6-311+G(2df,2pd) levels for the fluorine and the hydrogen analogues, respectively, provided rotational constants, dipole moment components, and the relative energies of the conformers to assist in the spectral assignment. In both molecules, the gauche-gauche conformer was identified by the ab initio calculations as the most stable. Agreement of the ab initio rotational constants with those from experiment was at worst 5%, with most rotational constants being predicted to within 2%.

Vibrational spectrum, ab initio calculations, conformational stabilities and assignment of fundamentals of the Ci conformer of 1,4-dichlorobutane.

The infrared and Raman spectrum of 1,4-dichlorobutane is reported in solid, liquid and gas. Ab initio calculations for the nine stable or metastable conformers of 1,4-dichlorobutane are reported for Moller-Ploessett second order electron correlation and B3LYP density functionals with a variety of basis sets, using approximations as high as 6-311+g(2d, 2p). Normal coordinate calculations were conducted for the nine conformers and the results used to provide assignments for some of the observed infrared and Raman bands. An attempt to use the assignments together with the ab initio intensities or Raman activities to investigate the composition of the liquid at room temperature proved modestly successful, and suggested that the populations are altered from those expected in the gas phase by interactions of the permanent electric dipole moments with the dipolar plasma in which the conformers are immersed in the liquid. A substantial disagreement between the Moeller-Ploessett and density functional results is reported, and the calculation of intensities and activities is insufficiently accurate to allow detailed interpretation of the spectrum of the room temperature liquid. A complete assignment of fundamentals is given for the conformer of Ci symmetry, and one Raman and one infrared band is identified with the C2h conformer. All the other infrared and Raman bands in the liquid or the gas are composites of several contributors.

Vibrational spectrum, ab initio calculation, conformational equilibria and torsional modes of 1,3-dibromopropane.

The infrared and Raman spectrum of 1,3-dibromopropane is reported in the crystalline, liquid and gaseous states. These measurements are compared to the results of ab initio calculations carried out using the 6-31+g* Gaussian basis set for a restricted Hartree-Fock computation. The calculation was repeated using second order Moeller-Ploesset perturbation theory to accommodate electron correlation using the 6-31 g* basis set. The three most stable conformers are GG (C2), AG (C1) and AA (C2v), where A and G stand for anti and gauche orientations of the bromomethyl group relative to the plane of the carbon atoms. The point group symmetry of each structure is given in parentheses. The fourth conformer, G'G (Cs) is of such high energy that it is not observed experimentally in isotropic media in either the infrared or Raman spectrum. In the crystalline state, comparison of the infrared and Raman spectrum with that calculated for the C2 conformer shows that only the GG (C2) conformer survives, and the doublet structure of many of the bands in the spectrum indicates at least two molecules per unit cell. The ab initio calculations predict and the temperature dependence of the Raman spectrum of the liquid confirms that the stability order is C2

Conformational stability from variable temperature infrared spectra of krypton solutions, ab initio calculations, vibrational assignment, and r0 structural parameters of 1,3-difluoropropane.

The infrared spectra (3200-400 cm(-1)) of krypton solutions of 1,3-difluoropropane, FCH2CH2CH2F, at variable temperatures (-105 to -150 degrees C) have been recorded. Additionally, the infrared spectra (3200-50 cm(-1)) of the gas and solid have been recorded as well as the Raman spectrum of the liquid. From a comparison of the spectra of the fluid phases with that in the solid, all of the fundamental vibrations of the C2 conformer (gauche-gauche) where the first gauche indicates the form for one of the CH2F groups and the second gauche the other CH2F, and many of those for the C1 form (trans-gauche) have been identified. Tentative assignments have been made for a few of the fundamentals of the other two conformers, i.e. C2v (trans-trans) and Cs (gauche-gauche'). By utilizing six pairs of fundamentals for these two conformers in the krypton solutions, an enthalpy difference of 277 +/- 28 cm(-1) (3.31 +/- 0.33 kJ mol(-1)) has been obtained for the C2 versus C1 conformer with the C2 conformer the more stable form. For the C2v conformer, the enthalpy difference has been determined to be 716 +/- 72 cm(-1) (8.57 +/- 0.86 kJ mol(-1)) and for the Cs form 971 +/- 115 cm(-1) (11.6 +/- 1.4 kJ mol(-1)). It is estimated that there is 64 +/- 3% of the C2 form, 34 +/-3% of the C1 form, 1% of the C2v form and 0.6% of the Cs conformer present at ambient temperature. Equilibrium geometries and total energies of the four stable conformers have been determined from ab initio calculations with full electron correlation by the perturbation method to second order as well as by hybrid density functional theory calculations with the B3LYP method using a number of basis sets. The MP2 calculations predict the C1 conformer stability to be slightly higher than the experimentally determined value whereas for the C2v and Cs conformers the predicted energy difference is much larger than the experimental value. The B3LYP calculations predict a better energy difference for both the C1 and C2v as well as for the Cs conformers than the MP2 values. A complete vibrational assignment is proposed for the C2 conformer and many of the fundamentals have been identified for the C1 form based on the force constants, relative intensities and rotational-vibrational band contours obtained from the predicted equilibrium geometry parameters. By combining previously reported rotational constants for the C2 and C1 conformers with ab initio MP2/6-311 + G(d, p) predicted parameters, adjusted r0 parameters have been obtained for both conformers. Comparisons are made with the parameters obtained for some other molecules containing the FCH2 group. The spectroscopic and theoretical results are compared to the corresponding properties for some similar molecules.

Vibrational spectrum, ab initio calculations, conformational equilibria and torsional modes of 1,3-dichloropropane.

Ab initio calculations are reported for three of four possible conformers of 1,3-dichloropropane. The fourth conformer, with Cs symmetry, has a predicted enthalpy difference of more than 1500 cm(-1) from the most stable conformer from each calculation regardless of the basis set used, so there is little chance of observing it. Thus, there is no evidence in the infrared or Raman spectrum of the presence of a fourth conformer. The order of stability given by the ab initio calculations is C2(GG)>C1(AG)>C2v(AA)>Cs(GG'), where A indicates the anti form for one of the CH2Cl groups and G indicates the gauche conformation for the other CH2Cl group relative to the plane of the carbon atoms. Almost every band observed can be confidently assigned to one or another of the conformers. Many observed bands proved to be of a composite nature, with several nearly coincident vibrations of different conformers contributing to the band contour. Nonetheless, a complete assignment of fundamentals is possible for the most stable C2 conformer, and 5 of the fundamentals of the C2v conformer and 13 those of the C1 conformer can be confidently assigned.

Binding efficiency and transport properties of molecularly imprinted polymer thin films.

A model system for the characterization of molecular recognition events in molecularly imprinted polymers (MIPs) is presented. The use of a biologically inspired, three-point hydrogen-bonding motif and a thin film polymeric matrix allows for pre- and post-polymerization binding properties to be characterized by infrared spectroscopy. A method to determine binding constants was developed and utilized before and after cross-linking. These values showed a 10-fold decrease in binding after polymerization, which was attributed to an increase in molecular confinement after polymerization and a change in the local structural environment of the binding cavity. Transport of the guest molecule was shown to be reversible.