Acetaldehyde absorption spectrum

As previously noted, formaldehyde does not present a significant absorption spectrum (without derivatives, see Section 4.1). On the contrary, acetaldehyde, butyraldehyde and benzaldehyde show absorption maxima of different intensities according to absorptivities (Fig. 30). For benzaldehyde, the peak position is close to the one of aromatic rings. 

It was originally thought that some OH radicals must abstract hydrogen atoms from ethylene to form C2H3 radicals (14), but it is now concluded that all OH radicals add to ethylene (Reaction 1) and that the -hydroxy-ethyl radicals enter into reactions, not all of which give rise to acetaldehyde (13). Other recent evidence also supports this view (4). The absorption spectrum of the -hydroxyethyl radicals is similar to that of the a-hydroxyethyl radicals which can be prepared from ethyl alcohol (13). 

FIGURE 14-6 Effect of solvent on the absorption spectrum of acetaldehyde. 

The absorption spectrum of 2-hydroxyethanal is shown in figure IX-C-1 as reported by Magneron et al. (2005). It has been pointed out that substitution of the electron-withdrawing —OH group on acetaldehyde results in a shift of the n n transition to shorter wavelengths, with a substantial decrease in overlap with the solar flux present in the lower troposphere. The cross sections at selected wavelengths are given in tabular form in table IX-C-1. 

Figure 19.18 1H NMR spectrum of acetaldehyde. The absorption of the aldehyde proton appears at 9.8 8 and is split into a quartet.

CXXXI. Its properties are those to be expected of such a structure for example, the UV-spectrum shows absorption at 224 m/u. (e = 14000) corresponding to one diene chromophore in the C4o-molecule, and oxidation by osmium tetroxide-sodium chlorate followed by periodate fission gives both acetaldehyde and formaldehyde. The Hofmann degradation can be completed by treatment of descurarine with alkali to yield the ditertiary ether base CXXVIII (129). 

Solution The spectrum shows an intense absorption at 1725 cm due to a cntbonyl group (perhaps an aldehyde. -CHO>, a series of weak absorptions from 1800-2000 cnt characteristic of aromatic compounds, and a C H absorption near 30(10 cm, also characteristic of aromatic compounds. In fact, the spectrum is chat of phenyl acetaldehyde. 

Aldehyde protons (RCHO) absorb near 10 5 in the Ml N MR spectrum and are very distinctive because no other absorptions occur in this region. The aldehyde proton shows spin-spin coupling with protons on the neighboring carbon, with coupling constant / 3 Hz, Acetaldehyde, tor example, shows a quartet at 9.8 5... 

The first absorption region of acetaldehyde extends approximately from 3480 A to 2300 A (ref. 2). The spectrum is discontinuous, between about 3480 and 3300 A, and the bands have distinct structure The structure becomes gradually diffuse below 3300 A, and turns into a continuum around 2730 A (ref. 2). The whole banded region is underlaid by a continuum. The maximum of the band intensities can be found at 3100 A, while that of the absorption observed (band+continuum) appears at 2890 A (ref. 2). The second absorption region commences around 2000 A. 

Both acetic acid and acetaldehyde have an absorption in the 3100 cm region of the infrared and are unlikely since no absorption in this region was observed. When the IR spectrum of honoopolymer PVC impregnated with acetyl chloride was measured, two absorptions in the carbonyl region are observed at 1776 and 1722 cm . These two absorptions correspond quite well with those of the degraded cc olymer. It does however indicate that the radical has abstracted a chlorine from the polymer, a process generally considered imlikely. 

---