Asymmetric induction by phase-transfer catalysis using chiral catalysts. Synthesis of 1,2-dichloroalkanes and acetylcyanohydrins

Asymmetric induction is observed in the additioin of chlorine to alkenes as well as in the synthesis of 0-acetyl cyanohydrins under phase-transfer conditions using (?)-benzylcinchonidinium chloride and (?)-N-dodecyl-N-methylephedrinium bromide as chiral catalysts.     

Vibrational spectra and rotational isomerism of 1,2-dimethyldisilane

The i.r. and Raman spectra of 1,2-dimethyldisilane and its Si-perdeuterated species have been measured for the liquid and solid states. Existence of rotational isomers about the SiSi bond was shown on the basis of the spectral examination and the normal coordinate treatment. The fundamental vibrations were assigned for the two possible rotational isomers.     

Vibrational frequencies and infrared absorption intensities of 1,2-dibromoethane

Infrared and Raman spectra of 1,2-dibromoethane CH₂BrCH₂Br and CD₂BrCD₂Br were observed in the liquid state, and the fundamental frequencies were determined by comparison with those of related molecules. Infrared absorption intensities of fundament bands were measured in the liquid state, and the intensity data were interpreted on the basis of the valence-optical theory. From the converged value of a population ratio, the energy difference between the trans and gauche isomers was determined, which was in good agreement with the value obtained from the temperature effect of the IR spectrum.     

Vibrational infrared intensities and polar tensors of 1,2-difluoroethylenes

The polar tensors of cis and trans-1,2-difluoroethylenes have been determined with new normal modes based in a reassignment of nu(7) and nu(12) bands of the trans isomers and frequency values corrected for Fermi resonances and phase shifts. The signs of the dipole moment derivatives (and its directions, for B(u) symmetry species) were considered to be those of MP2/6-31G** estimates. Root mean square errors calculated for the new tensor element values from each pair of isotopomers (trans-1,2-C(2)H(2)F(2)/trans-1,2-C(2)D(2)F(2) and cis-1,2-C(2)H(2)F(2)/cis-1,2-C(2)D(2)F(2)) show that the new polar tensor sets fit the isotopic invariance criterion better than previously reported sets. The accuracy of polar tensor transference procedures was tested by calculating the infrared intensities of trans-1,2-C(2)H(2)F(2) through the new polar tensors of the cis isomer. The resulting estimates are very accurate and also support the new band assignment, though the A(6) intensity remains still somewhat underestimated.     

Vibrational frequencies and structural determination of 1,1-difluoro-1,2-propadiene

The normal mode frequencies and corresponding vibrational assignments of 1,1-difluoro-1,2-propadiene in C_2v symmetry are examined theoretically using the 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of 11 types of motion (C=C stretch, C–H stretch, C–F stretch, CH₂ scissors, CF₂ scissors, CH₂ wag, CF₂ wag, CH₂ rock, CF₂ rock, CF₂ twist, and C=C=C bend) predicted by a group theoretical analysis. Comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Predicted infrared intensities and Raman activities are reported. Predicted normal mode frequencies of 1,1-difluoro-1,2-propadiene-d₂ are reported.     

Vibrational spectra of cis- and trans-1,2-dimethyl-3-bromocyclopropane

The infrared and Raman spectra of cis- and trans-dimethylbromocyclopropane have been recorded from 4000 to 50 cm⁻¹. An assignment of the majority of the fundamentals is proposed and compared to those of related molecules. Definite and consistent trends in a number of normal modes of the ring and the methyl groups with the nature, position and number of the substituents have been found. Clear evidence has been obtained for steric interaction between the three substituents in cis-position.     

Vibrational analysis of hydroxyacetone

In order to be able to fully understand the vibrational dynamics of monosaccharide sugars, we started with hydroxyacetone CH2OHCOCH3, and glycolaldehyde CH2OHCOH, which are among the smallest molecules that contain hydroxyl and carbonyl group on neighboring carbon atoms. This sterical configuration is characteristic for saccharides and determines their biochemical activity. In this work vibrational analysis of hydroxyacetone was undertaken by performing the normal coordinate analysis for glycolaldehyde first, and transferring these force constants to hydroxyacetone. The observed Raman and infrared bands for 90 wt.% solution of hydroxyacetone in water (acetol) were used as a first approximation for the bands of free hydroxyacetone. The number of observed Raman and infrared bands for acetol exceeds the number of calculated values for the most stable hydroxyacetone conformer with Cs symmetry, which suggests more than one conformer of hydroxyacetone in water solution. In particular, there are two bands both in infrared (1083 and 1057 cm(-1)) and in Raman spectrum (1086.5 and 1053 cm(-1)) that are assigned to the CO stretching mode and this is one of the indicators of several hydroxyacetone conformers in the solution. Additional information was obtained from low temperature Raman spectra: at 240 K a broad asymmetric band centered around 280 cm(-1) appears, suggesting a disorder in the orientation of hydroxyl groups. Glassy state forms at approximately 150K. The broad band at 80 cm(-1) is assigned to frozen torsions of hydroxymethyl groups.     

Vibrational frequencies and structural determination of 1,3-difluoro-1,2-propadiene

The normal mode frequencies and corresponding vibrational assignments of 1,3-difluoro-1,2-propadiene in are examined theoretically using the GAUSSIAN 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of eight types of motion (CC stretch, C–H stretch, C–F stretch, H–C–F scissors, H–C–F wag, H–C–F rock, H–C–F twist, and CCC bend) predicted by a group theoretical analysis. Comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors are derived. Predicted infrared and Raman intensities are reported.     

Vibrational analysis of halogenated derivatives of cyclobuten-3,4-dione I. 1,2-Dichloro-, 1-chloro-2-bromo-, and 1,2-dibromocyclobuten-3,4-dione

The polarized Raman spectrum of solutions, and the infra-red spectra of solutions and isooriented films in polarized radiation have been measured for 1,2-dichloro- and for the previously unknown 1-chloro-2-bromo- and 1,2 dibromocyclobuten-3,4-dione. A normal coordinate analysis has been carried out with the aims of obtaining an acceptably low dispersion force field and a good agreement with the experimental frequencies.     

Vibrational spectra of 1,2-diaminobenzene, 4,5-dimethyl-1,2-diaminobenzene and catechol and their SER spectra

The Raman and IR spectra of 1,2-diaminobenzene and 4,5-dimethyl-1,2-diaminobenzene are reported and assignments of fundamental modes proposed. The surface-enhanced Raman spectra (SERS) of catechol, 1,2-diaminobenzene and 4,5-dimethyl-1,2-diaminobenzene on gold and silver colloids were obtained. FT-SERS of the three molecules are also briefly reported.     

Vibrational spectra,packing calculations and crystal structure of 1,2-diiodobenzene

The vibrational spectra of crystalline 1,2-diiodobenzene are presented. Spectroscopic evidence in combination with packing and lattice frequence calculations point to a tetramolecular unit cell, space group C⁵_2h- Approximate molecular positions are given.     

Vibrational spectra and structure of cis- and trans-1,2- dimethoxyethylenes

The vapor, liquid and CCl₄ solution infrared spectra of cis- and trans-1,2-dimethoxyethylene were recorded in the region 250–4000 cm^?1. The laser-Raman spectra were obtained in the liquid state only. The vibrational spectra show that at least two rotational isomers exist for each molecule. Further, the spectra indicate that for both the cis- and trans molecules, one of the rotational isomers has at least one planar conformer. Some vibrational assignments are made for the observed infrared and Raman bands of the cis- and trans- 1,2-dimethoxyethylenes.     

Vibrational analysis of some trimethylalkanes

Liquid and solid-state infrared spectra were obtained for 2,2,3-trimethylbutane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane and 2,3,3-trimethylpentane, and were interpreted with the aid of normal coordinate calculations. Trimethylbutane, 2,2,3-trimethylpentane and 2,2,4-trimethylpentane each exist as only one conformer, but either two or three conformers of 2,3,3-trimethylpentane are present in the liquid state. Only one conformer is present in the crystalline solid, and it was identified as one with only four of the five chain carbons coplanar. The average error for 246 calculated frequencies assigned to observed values for the six molecules is 5.2 cm⁻¹, or 0.59%     

Vibrational analysis of alkyl xanthates

Rotational isomers are indicated in the Raman spectra of sodium ethyl and other xanthates. Vibrational bands useful for characterizing xanthate solids and aqueous solutions are given. Vibrational analyses are reported for sodium ethyl xanthate, trans and gauche forms, and the methyl and isopropyl analogs using a Cartesian coordinate force field derived from ab initio molecular orbital calculations.     

Vibrational analysis of 1,4-diiodobutane

Infrared and Raman spectra were obtained for 1,4-diiodobutane, and normal-coordinate calculations were made using a transferred 48-parameter modified v force field. This compound sometimes crystallizes in the GG' conformation with C₂ symmetry and sometimes in the TG conformation. No evidence was obtained for the presence of the TT (C_2h symmetry) or GG (C_i) conformers, but one or two additional conformers are present that must have a nonplanar chain of carbon atoms.     

Vibrational analysis of aromatic esters

An eighty seven parameter valence force field for aromatic esters has been determined. Forty two force constants were assigned values determined from earlier work on alkyl benzenes and aliphatic ethers. Forty-five force constants were adjusted using 345 observed frequencies for methyl benzoate, methyl-d₃ benzoate, ethyl benzoate, ethyl-d₅ benzoate, dimethyl terephthalate, dimethyl terephthalate-d₄, diethyl terephthalate, dibenzoyl ethylene glycol, and dibenzoyl ethylene-d₄ glycol. Neglecting the CH-stretching modes, the average error betweeen calculated and observed frequencies was approximately 7.2 cm⁻¹.     

Vibrational analysis of 1,1-dichlorobutane

IR and Raman spectra have been obtained for 1,1-dichlorobutane and interpreted with the aid of normal coordinate calculations. It is concluded that this compound exists in three conformations in the liquid and glassy solid states but crystallizes only in the conformer that has all four carbons coplanar and both chlorines out of that plane (C_s symmetry).     

Vibrational analysis of 1,4-dibromopentane

Infrared and Raman spectra have been obtained for 1,4-dibromopentane and interpreted with the aid of normal coordinate calculations. It is concluded that all six conformers resulting from rotation about the C₁-C₂ and C₃-C₄ bonds probably exist in the neat liquid and amorphous solid, and that the compound crystallizes in the P_HS_HH conformer that has the two bromine atoms on opposite sides of the plane of carbon atoms. The compound therefore behaves like 1,3-dibromopropane and 1,4-dibromobutane.     

Vibrational analysis of 3-trifluoromethylphenol

The molecular geometry and molecular vibrations of 3-trifluoromethylphenol have been investigated by means of quantum chemical calculations and vibrational spectroscopy. The computations indicated the preference of the conformer with the OH hydrogen pointing in the direction of the trifluoromethyl group by 0.9 kJ/mol with respect to the anti conformer. FT-IR spectra of the vapour and CCl₄ solution as well as FT-IR and FT-Raman spectra of the pure liquid have been recorded in the range of 4000–150 cm⁻¹. The interpretation of the spectra was based on a scaled quantum mechanical (SQM) analysis for which the initial force field was calculated at the Becke3-Lee-Yang-Parr (B3LYP) DFT level supplemented with a 6-311++G** basis set. Using 11 scale factors refined in the present study an rms deviation of 7.6 cm⁻¹ between the experimental and SQM frequencies has been achieved. On the basis of the computations 40 of the total of 42 fundamentals of the title compound have been assigned.