<p>DFT(B3LYP)/6–311++G(d,p) calculated conformers of ethyl maltol.</p> Full article ">Figure 2
<p>As-deposited IR spectrum of ethyl maltol isolated in an Ar matrix, at 14.5 K (top) and B3LYP/6–311++G(d,p) calculated (scaled) IR spectrum of conformer I of the molecule (bottom).</p> Full article ">Figure 3
<p>Difference IR spectrum of ethyl maltol in an Ar matrix (41.5 K <span class="html-italic">minus</span> as-deposited matrix) (<b>a</b>), and B3LYP/6–311++G(d,p) simulated IR difference spectrum (centrosymmetric dimer <span class="html-italic">minus</span> conformer I) (<b>b</b>). In the calculated (scaled) spectrum, IR intensities of the dimer were divided by 4; the intensity scale before and after the break are different to allow a better comparison with the experiment.</p> Full article ">Figure 4
<p>Difference IR spectrum obtained by subtracting the spectrum of the as-deposited Ar matrix of ethyl maltol from that obtained after 1 min of irradiation (<span class="html-italic">λ</span> > 235 nm) (<b>a</b>), and simulated spectra constructed based on the DFT(B3LYP)/6–311++G(d,p) calculated IR spectra of the identified photoproducts (<b>7</b> and <b>8</b>; see <a href="#spectroscj-02-00013-f006" class="html-fig">Figure 6</a>) and of ethyl maltol (conformer I) (<b>b,c</b>). In the calculated spectra, the frequencies were scaled as described in <a href="#sec3-spectroscj-02-00013" class="html-sec">Section 3</a>, and the intensities were multiplied by different factors for each compound to facilitate comparison with the experimental data.</p> Full article ">Figure 5
<p>Difference IR spectrum obtained by subtracting the spectrum of 1 min irradiated Ar matrix of ethyl maltol from that obtained after 20 min of irradiation (<span class="html-italic">λ</span> > 235 nm) (<b>a</b>), and simulated spectra constructed based on the DFT(B3LYP)/6–311++G(d,p) calculated IR spectra of the identified photoproducts <b>7</b>, <b>9,</b> and <b>11</b> (see <a href="#spectroscj-02-00013-f006" class="html-fig">Figure 6</a>) and of ethyl maltol (conformer I) (<b>b,c</b>), and of smaller molecules resulting from photolysis (<b>d</b>). The spectra of these latter species are shown separate from those of <b>7</b>, <b>9</b>, <b>11,</b> and ethyl maltol for better viewing, and the spectrum of compound <b>8</b> (that are pointing down in the experimental spectrum) were omitted from spectra b and c for simplicity since they correspond to comparatively small features. Cp denotes cyclopropenone. In the calculated spectra, frequencies were scaled as described in <a href="#sec3-spectroscj-02-00013" class="html-sec">Section 3</a>, and intensities were multiplied by different factors for each compound to facilitate comparison with the experimental data.</p> Full article ">Figure 6
<p>Proposed reaction scheme for the results of irradiation of ethyl maltol in an argon matrix (<span class="html-italic">λ</span> > 235 nm). The radical <b>6</b> was not observed. Products <b>7</b> and <b>8</b> were observed after 1 min of irradiation (blue squares). The latter was subsequently transformed into other species. The products observed after 20 min of irradiation are represented in green squares. The numbers in parentheses correspond to the electronic energies of the different species relative to the reactant, in the ground electronic state, except in the case of the number associated with the cyclopropenone photodecomposition that corresponds to the decrease in electronic energy of the reaction.</p> Full article ">Scheme 1
<p>Ethyl maltol (<b>1</b>), maltol (<b>2</b>), kojic acid (<b>3</b>), pyromeconic acid (<b>4</b>), and ethylfurfuryl alcohol (<b>5</b>).</p> Full article ">