Abstract:
Acid halides of acrylic acid and halogen substituted acrylic acids have C-C bond as axis of internal rotation and they may exist as a mixture of rotational isomers. Infrared spectroscopic investigations of these compounds and other structurally similar molecules, crotonyl halides, fumaryl chloride, and bromo and iodoacetyl chloride are reported. Spectroscopic data for more than twenty compounds is contained in this report and analysed in term of existence of rotational isomers wherever possible. In many cases observed spectral features are best explained on the basis of more than one isomers. Therefore the observed bands in the spectra are assigned to rotational isomers in each case and the vibrational frequency assignments are rationalized in term of various factors, such as conjugation, mass and field effects (inductive, mesomeric) hydrogen bonding.
Normal coordinates analysis calculation for iodo-acetyl chloride is made to show how this approach helps in obtaining the azimuthal angle of internal rotation as for geometry of the isomer is concerned.
Infrared spectroscopic investigation of halogenated acrylic acids indicate that they exist as dimers formed as a result of strong hydrogen bonding.
Acrylic acid is a basic unit in certain industrially important polymers. Reactions involving acrylic acid and acid halides of acrylic acids and substituted acrylic acids can be best understood after proper conformational studies. The problem, on the other hand, is of theoretical importance. The lack of any satisfactory theory to explain potential barriers and enthalpy differences in the class of compounds is generally felt. It is hoped that the results of present investigation will help in understanding the problem from theoretical viewpoint on the analytical side characterization of group frequencies to each isomer present will help in ready identification of compounds.
