Aldehydes infrared absorption frequencies

Aldehydes Amides Carboxylic acid anhydrides Carboxylic acids Esters Ketones and functional groups, 56 infrared absorption frequencies, 519,... 

Different types of carbonyl groups give characteristic strong absorptions at different positions in the infrared spectrum. As a result, infrared spectroscopy is often the best method to detect and differentiate these carboxylic acid derivatives. Table 21-3 summarizes the characteristic IR absorptions of carbonyl functional groups. As in Chapter 12, we are using about 1710 cm for simple ketones, aldehydes, and acids as a standard for comparison. Appendix 2 gives a more complete table of characteristic IR frequencies. 

Ultraviolet and Infrared Spectra.—The effect of conjugation in the excited state of some silicon-substituted thiophens has been discussed. The u.v. and i.r. characteristic absorption spectra of some pairs of cis- and rra/75-isomers of 2 - and 3 -substituted 2-styrylthiophens have been determined. It is claimed that the spectra of the stereoisomers are sufficiently different to assign the configuration. The i.r. and Raman spectra of 4-chloro-, 4-bromo-, 4-iodo-, and 4-cyano-2-fluoro-thiophens have been studied in the region 500—540 cm . The fundamental frequencies have been assigned, and normal co-ordinate calculations have been performed. The force constants were adjusted to reproduce accurately the fundamental frequencies. Thermodynamic functions and mean amplitudes of vibration for these molecules were also calculated. Thiophen-2-aldehyde and 19 related aldehydes have been studied under high resolution in the i.r. C=0 region. 

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