Stuart W. Charles

The vibrational spectra, rotational isomerism, normal coordinate analysis and mean amplitudes of ethyl formate, ethyl chloroformate and ethyl cyanoform

Abstract The infrared spectra of ethyl formate, chloroformate, and cyanoformate in the liquid phase have been recorded in the region 4000–4020 cm −1 , and in the solid and vapour phase and in solution in the region 4000–4200 cm −1 . Evidence is reported for the existence of two rotameric forms in each case. Normal coordinate calculations are reported for both rotameric forms of the first two esters, and assignments based on potential energy distributions are given. These assignments show considerable mixing of the normal modes and suggest the inadequacy of simple assignments made by comparison with related molecules. Calculated mean amplitudes are also reported for the first two molecules.

Infrared spectrum and rotational isomerism of acrylic acid

Abstract The infrared spectrum of monomeric acrylic acid has been observed between 200 and 4000 cm−1 for a dilute sample in an inert matrix at 25 K. Absorption bands due to the cis and trans rotamers have been distinguished using UV irradiation experiments and identified on the basis of theoretical calculations. Assignments have been made of the observed absorptions to normal modes of vibration for both rotamers.

Infrared spectra and rotational isomerism of epifluorohydrin and other propene oxide derivatives

Abstract The infrared spectrum for the vapour, liquid and solid states of epifluorohydrin has been studied, and evidence has been obtained for the presence of rotational isomers. The dominant conformer in all phases corresponds to a gauche structure, which was the only form identified in the vapour by microwave spectroscopy [1]. Similar evidence for conformational equilibria has been found for the chloro, bromo and iodo derivatives, and the enthalpy differences between the rotational isomers of these compounds were measured respectively as 4580 ± 970, 3950 ± 400, and 2350 ± 170 J mol −1 respectively. At low temperatures, epiiodohydrin was found to crystallize in one of two possible crystalline phases. These two phases correspond to the two rotational isomeric conformations of the molecule.

Infrared spectra and rotational isomerism of ethyl fluoroformate and ethyl propiolate

Abstract The infrared absorption spectra of ethyl fluoroformate and ethyl propiolate have been examined in the vapour, solution and solid states. For both esters evidence is found of rotational isomerism arising from internal rotation about the O-C 2 H 5 bond, in close agreement with previous work on other ethyl esters.

The vibrational spectra and rotational isomerism of monochloromethyl acetate and methyl oxalyl chloride

Abstract The IR spectra of monochloromethyl acetate and methyl oxalyl chloride have been studied for the vapour, liquid and solid states. For the first ester only one conformation is present and it has a planar arrangement of heavy atoms with the chlorine directed away from the carbonyl group and with a s - cis arrangement for the basic ester framework. For methyl oxalyl chloride, evidence is presented for the presence of two rotamers, the more stable of which is probably planar with a trans arrangement of carbonyl groups.

The infrared spectra and conformation of methyl and ethyl propenyl ethers

Abstract The infrared spectra of the cis and trans geometric isomers of methyl and ethyl propenyl ethers have been recorded in the liquid and vapour phase, in the region 4000-200 cm −1 . Solid phase spectra have also been recorded for all but trans methyl propenyl ether. Evidence is given for the existence of two rotameric forms for both the trans compounds, in each case the more stable conformer being planar s-cis; but a single non-planar conformation is suggested for the two cis isomers. The enthalpy difference between the two rotameric forms in trans ethyl propenyl ether was found to be 4.6 ± 1.0 kJ mol −1 (1100 ± 250 cal mol −1 ).

Infrared spectra and molecular conformation of butyronitrile and methyl thioacetonitrile

Abstract The infrared absorption spectra of two related compounds, butyronitrile (CH 3 CH 2 -CH 2 CN) and methylthioacetonitrile (CH 3 SCH 2 CN) have been examined in the liquid and solid phases. Vapour phase spectra of butyronitrile have also been recorded. Evidence is given for the existence of two rotational isomers trans and gauche , for both compounds. In both cases the energy difference between the two rotamers appears to be small with the gauche form identified as the low energy conformer for butyronitrile. For methylthioacetonitrile it was not possible to determine the more stable rotational isomer.

Vibrational spectra, barriers to internal rotation and conformation of propargyl methyl ether and methoxyacetonitrile

The infra-red absorption spectra of propargyl methyl ether and the isoelectronic compound methoxyacetonitrile in the vapour, liquid and solid states have been examined. The spectra of both ethers indicate the presence of a conformational equilibrium of trans and gauche forms, the latter being the more stable in both cases. Calculations of the magnitude of the barrier to rotation of the methyl group and of the barrier to rotation about the O—CH2X bond have been made for the gauche rotamer of both compounds.

Vibrational spectra and rotational isomerism of methyl and ethyl cyanoacetate

The infra-red absorption spectra of liquid and solid methyl cyanoacetate and ethyl cyanoacetate have been examined. For the methyl ester, evidence is found of rotational isomerism arising from internal rotation about the NCH2C—C bond. The enthalpy difference between the two stable rotameric forms (with the CN group cis and gauche to the CO bond) was found to be 4060 ± 300 J mol–1.For ethyl cyanoacetate, the infra-red spectrum suggests the presence of several rotamers brought about by rotation about both the NCH2C—C and the O—C2H5 bonds.

Infra-red spectrum and conformations of 2,2,2-trifluoroethyl vinyl ether

The infra-red spectrum of 2,2,2-trifluoroethyl vinyl ether has been studied for the vapour, liquid and solid states. Evidence is presented for the presence of rotational isomers in the vapour and liquid phases arising from the internal rotation about the central bond of the CH2CH—OC fragment. Two crystalline solid phases exist and evidence is proposed for the occurrence of more than one rotamer in one of these solid phases. The least stable of these latter conformations is brought about by rotation about the CH2CHO—C bond.The dipole moment has been measured in benzene solution at 293 K and found to be 2.9 ± 0.2 D.