Acrolein, dipole moment

Yonezawa et al. 32b> have calculated the dipole moment of cis-1,3-butadiene together with three oxygen-containing compounds. In only one case, trans-acrolein, is it possible to make a comparison with an experimental value, and here the calculated value is 0.45 debyes greater than the observed one. 

For this study we have used methylen-cyclopropene (MCP) and acrolein (ACRO) in two solvents, an apolar (dioxane) and a polar one (acetonitrile). The selected transitions can be seen as representative examples of different types of electronic transitions for which different solvent responses can be studied for MCP the first 77 - 77 transition for MCP, and the first n -> 77 and 77 -> 77 transitions for ACRO. We note that in MCP the resulting excited state is characterized by a dipole moment which has an opposite direction with respect to that of the ground state, whereas in ACRO, the n -> 77 and 77 -> 77 transitions are characterized by a decrease and an increase in the dipole moment passing from ground to excited state, respectively. 

FIGURE 5. Total net charges and 7c-electron densities (in parenthesis) from CNDO/S calculations for vinylamine, acrolein and 3-dimethylaminoacrolein. Experimental dipole moments are from References 17, 105 and 106, respectively... 

If the molecule contains an ethylenic group C=C in addition to the carbonyl group, the molecular resonance is increased and the dipole moment raised. Thus in acrolein, GH2=CHCHO, the dipole moment measured in solution is 2-88 D, a value greater by 0 39 D than the dipole moment of acetaldehyde also measured in solution, 2 49 D. This is due to the contribution of the structure... 

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