Isopropylidene derivatives absorption

Substitution of a phenyl residue in the 4-position of the selenazole ring causes only a minor alteration in the position of the absorption maximum. By contrast, the benzylidene compounds are markedly bathochromically shifted compared to the isopropylidene derivatives. Thus the absorption is caused by the whole of the conjugated system, which can be compared to that found in amino derivatives of... 

Fig. 3.—Fourier-transform, Proton Magnetic Resonance Spectra45 of 6-Deoxy-l,2 3,4-di-O-isopropylidene-6-phthalimido-a-D-gaIactopyranose (54) (0.06 mg) at 90 MHz, Obtained by Transformation (N = 4,096) of the Free-induction Decay Signal (1,024 Datum Points, see Fig. 2), After the Appendation of 3,072 Zero, Datum Points ( Zerofilling, See Text), [(a) Spectrum associated with the real part of the transform, and (b) with the imaginary part (c) absorption-mode spectrum computed by phase correction of the spectrum in (a) and (d) dispersion-mode spectrum computed by phase correction of the spectrum in (b). Parameters for phase correction, A —255° and B —215°. Note that the phase of the tetramethylsilane and chloroform signals in (c) is slightly different from that of the carbohydrate derivative. By coincidence, the peak for residual water in spectrum (c) has almost the same intensity as the methyl signals, and could have been mistaken for one, had other spectra not been recorded.]...

Of the compounds reported to be crystalline, most are obviously not free aldehydes as they exhibit no aldehyde absorption in the infrared. The only exception, so far, seems to be methyl 2-formyl-3,4-0-isopropylidene-/3-L-pentoside. The compounds can exist as internal hemiacetals, or dimers, as shown for l,2-0-isopropylidene-a-D-a 3/lo-pentodialdo-l,4-furanose, as hemialdals (cyclization by the addition of water across two aldehyde groups) as suggested for the dialdoses from the splitting of two streptamine derivatives, or as hydrates, as proposed for D-gluco-hexodialdose. ... 

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