Formaldehyde: Comprehensive Spectral Investigation as a Function of Solvent and Temperature

Abstract

Absorption, emission, and NMR studies indicate that: (1) Formaldehyde exists as a monomer (form A) in nonpolar solvents to a temperature of approximately −95°C, (2) at −95°C in nonpolar solvents, formation of a formaldehyde polymer (form C) begins which is thermally reversible at temperatures > −90°C. The form C also exists at room temperature in water, dimethyl sulfoxide, dimethylformamide, and tetrahydrofuran. The formaldehyde-formaldehyde interaction is principally of a dipole-dipole type. (3) Formaldehyde can act as a hydrogen-bonding donor or acceptor in a complex with solvent molecules or silica gel (form B). In aromatic hydrocarbons, formaldehyde acts as a donor whereas in 2-methyltetrahydrofuran, chloroform, and silica gel it acts as an acceptor. Also, in 2-methyltetrahydrofuran, forms A and B exist in addition to C. Monomer formaldehyde exhibits a fluorescence from the lowest Sn,π* state in nonpolar solvents to −95°C. Both the forms B and C exhibit emission. In addition to the classification of the forms of formaldehyde, it is possible to classify the solvents into four main groups based on the rate of formation of paraformaldehyde or the fact that formaldehyde essentially totally reacts (strong hydrogen-bond donors or molecules with active α-hydrogen atoms).

A multiconfiguration self-consistent field/molecular dynamics study of the (n→π*)1 transition of carbonyl compounds in liquid water

“…The formaldehyde spectrum in aqueous solution is complicated due to the formation of oligomers 44 and in acetaldehyde there is gem-diol 45 ͑acetal͒ formation. The only experimental result 46 available is 4.9Ϯ0.5 kcal/mol for acetone in liquid water.…”

Two-response-time model based on CM2/INDO/S2 electrostatic potentials for the dielectric polarization component of solvatochromic shifts on vertical excitation energies

“…We note that \documentclass{article}\pagestyle{empty}\begin{document}$\widetilde A\,^{1}A_{2}\leftarrow\widetilde X\,^{1}A_{2}$\end{document} is an electric dipole forbidden transition which is made weakly allowed by vibronic interaction. We also note that, in certain respects, acetone is the simplest carbonyl compound that is well suited for a study such as the present one because aldehyde spectra are complicated by gem ‐diol (acetal) formation 55, and formaldehyde spectra are additionally complicated by polymerization to paraformaldehyde 56.…”

From hydrogen bond to bulk: Solvation analysis of then-?* transition of formaldehyde in water

“…As a consequence, this transition suffers a blue shift when formaldehyde is solvated in water. The amount of this blue shift is not well determined experimentally or theoretically, but it is believed to be larger than 2000 cm −1 3–5, with a very large broadening of about 4000 cm −1 4. This solvatochromic blue shift has been analyzed in several previous theoretical studies 5–12.…”