Acetaldehyde spectrum

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.

C Nuclear magnetic resonance spectrum, acetaldehyde, 732 acetophenone, 732 anisole, 672 benzaldehyde, 732 benzoic acid, 771 p-bromoacetophenone, 449 2-butanone, 449, 732 crotonic acid. 771 cyclohexanol, 634 cyclohexanone, 732 ethyl benzoate, 477 methyl acetate, 443 methyl propanoate, 450 methyl propyl ether, 672... 

Nuclear magnetic resonance spectrum, acetaldehyde, 731 anethole, 683 bromoethane, 460... 

From the Raman spectrum of acetaldehyde adsorbed on silica gel... 

The aldehydes, specifically formaldehyde and acetaldehyde, are rnidway in this spectrum. 

In the late 1950s the subtle and serious consequences of methyl mercury exposure became evident in Minamata, Japan. Initially, early signs of uncoordinated movement and numbness around the lips and extremities, followed by constriction in visual fields in fishermen and their families, baffled health experts. Developmental effects were clearly evident in infants who exhibited subtle to severe disabilities. This spectrum of adverse effects was finally related to methyl mercury exposure from consumption of contaminated fish. Minamata Bay was contaminated with mercury and methyl mercury from a factory manufacturing the chemical acetaldehyde. Mercury was used in the manufacturing process, which also resulted in both mercury and methyl mercury being discharged into Minamata Bay. The fish in the bay accu-... 

Consider acetaldehyde, CH3CHO. Figure 8.3 shows a for the methyl and CHO protons to differ substantially, so that Vq ax Jax- The low barrier to internal rotation causes condition (1) to be satisfied. Hence the first-order analysis of the preceding paragraphs is applicable. We have an A3X case and the spectrum consists of a doublet (from the methyl protons) whose lines are of equal intensity and a quartet (from the CHO proton) whose lines have the intensity ratios 1 3 3 1 the doublet and quartet are well separated and show the same splitting (Fig. 8.9). 

In the past 10 years a large number of organic molecules have been found in interstellar dust clouds mostly by emission lines in the microwave region of the spectrum (for a summary see Ref. 38). The concentration of these molecules is very low (a few molecules per cm3 at the most) but the total amount in a dust cloud is large. The molecules found include formaldehyde, hydrogen cyanide, acetaldehyde, and cyanoacetylene. These are important prebiotic molecules, and this immediately raises the question of whether the interstellar molecules played a role in the origin of life on the earth. In order for this to have taken place it would have been necessary for the molecules to have been greatly concentrated in... 

The microwave spectrum of the normal argon-acetaldehyde and of the Ar-CHsCDO van der Waals dimer has been used to determine their structure646 which was found to be a non-planar skew, with the Ar binding on top of the C—C—O triangle. The planar or nearly so structure of the Ar-formic acid van der Waals dimer has also been determined647 from assigning the rotation spectrum of normal, Ar, DCOOH and HCOOH isotopomers. 

The n.m.r. spectra of the conjugate acids of aldehydes can similarly be observed in the same medium at — 60°. The spectrum of acetaldehyde, for example, clearly indicates the presence of both the cis and trans isomers (11) and (12) of its conjugate acid. 

When acetaldehyde is dissolved in methanol, a reaction takes place we know this because the IR spectrum of the mixture shows that a new compound lias been formed. However, isolating the product is impossible it decomposes back to acetaldehyde and methanol. 

We have established that the formation of enols is catalysed by acids and bases. The reverse of this reaction—the formation of ketone, from enol—must therefore also be catalysed by the same acids and bases. If you prepare simple enols in the strict absence of acid or base they have a reasonable lifetime. A famous example is the preparation of the simplest enol, vinyl alcohol, by heating ethane-1,2-diol (glycol—antifreeze) to very high temperatures (900 °C) at low pressure. Water is lost and the enol of acetaldehyde is formed. It survives long enough for its proton NMR spectrum to be run, but gives acetaldehyde slowly. 

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