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Using heavy atom rare gas matrix to control the reactivity of 4-methoxybenzaldehyde: A comparison with benzaldehyde
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10.1063/1.3701734
/content/aip/journal/jcp/136/14/10.1063/1.3701734
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/14/10.1063/1.3701734

Figures

Image of Scheme 1.
Scheme 1.

Conformers of p-anisaldehyde.

Image of Scheme 2.
Scheme 2.

Main products of UV-induced transformations of p-anisaldehyde and benzaldehyde isolated in Ar and Xe matrices.

Image of Scheme 3.
Scheme 3.

From left to right: benzvalene, fulvene, Dewar benzene, benzoyl radical, and O-cis and O-trans conformers of p-methoxybenzoyl radical.

Image of Scheme 4.
Scheme 4.

Selected structures of closed- and open-ring ketenes isomeric of p-anisaldehyde. The closed-ring species, (4-methoxycyclohexa-2,4-dien-1-ylidene)methanone, may exist in two conformers, differing by internal rotation about the C–O(CH3) bond; in the electronic ground state, the less stable form has a calculated relative energy of 15.7 kJ mol‑1 with respect to the most stable form (left most form in the figure). The open-ring ketene may exist in both Z and E forms about the central bond, each isomer possessing several conformers (see Figures S2 and S3, supplementary material).51

Image of Scheme 5.
Scheme 5.

Photochemical reaction pathways for matrix-isolated p-anisaldehyde and benzaldehyde. IC, internal conversion; ISC, intersystem crossing; R = H or OCH3; Sn (n = 0, 1, 2, 3) lowest energy singlet states; T, generic triplet state.

Image of FIG. 1.
FIG. 1.

(a) Spectrum of a genuine sample of anisole in a xenon matrix at 30 K obtained in a separate experiment; (b) difference spectrum: the spectrum recorded after UV irradiation (10 min with λ > 234 nm + 5 min with λ > 200 nm) of p-anisaldehyde in Xe matrix minus the spectrum of the same sample recorded before any irradiation. Growing bands show upwards; (c) spectrum of p-anisaldehyde in a xenon matrix at 30 K (as deposited).

Image of FIG. 2.
FIG. 2.

Left panel: (a) Spectrum of benzaldehyde in a xenon matrix at 30 K (as deposited); (b) difference spectrum: the spectrum recorded after UV irradiation (180 min with λ = 250 nm) of benzaldehyde in Xe matrix minus the spectrum of the same sample recorded before any irradiation. Growing bands show upwards; (c) spectrum of a genuine sample of benzene in a xenon matrix at 30 K obtained in a separate experiment. Right panel: (a) spectrum of benzaldehyde in an argon matrix at 15 K (as deposited); (b) difference spectrum: the spectrum recorded after UV irradiation (165 min with λ = 250 nm) of benzaldehyde in Ar matrix minus the spectrum of the same sample recorded before any irradiation. Growing bands show upwards; (c) spectrum of a genuine sample of benzene in an argon matrix at 15 K obtained in a separate experiment.

Image of FIG. 3.
FIG. 3.

(a) Spectrum of p-anisaldehyde in an argon matrix at 15 K (as deposited); (b) difference spectrum: the spectrum recorded after UV irradiation (40 min with λ > 234 nm) of p-anisaldehyde in Ar matrix minus the spectrum of the same sample recorded before any irradiation. Growing bands show upwards; (c) simulated infrared spectrum of the most stable conformer of the closed-ring ketene isomer of p-anisaldehyde, (4-methoxycyclohexa-2,4-dien-1-ylidene)methanone (abbreviated in figure as “Ketene”).

Image of FIG. 4.
FIG. 4.

(a) Difference spectrum showing changes induced by UV irradiation (40 min with λ > 234 nm) of p-anisaldehyde in an argon matrix (the same spectrum as in Figure 3(b), growing bands show upwards); (b) simulated difference spectrum: most stable conformer of the closed-ring ketene isomer of p-anisaldehyde minus p‑anisaldehyde (55% O‑trans + 45% O-cis); (c) simulated difference spectrum: most stable conformer (E4 form; see Figure S2 in supplementary information)51 of the open-ring ketene isomer of p-anisaldehyde minus p‑anisaldehyde (55% O‑trans + 45% O-cis).

Image of FIG. 5.
FIG. 5.

Comparison of the infrared spectra of photoproducts obtained by UV-irradiation of benzaldehyde (a, b) and p-anisaldehyde (c, d) in xenon (a, c) and argon (b, d) matrices. The difference spectra shown in frames a, b, c, d correspond to the difference spectra shown in the middle frames of Figure 2 (left panel), 2 (right panel), 1, and 3, respectively. The negative bands due to the reactants are truncated. The asterisks indicate bands due to the C=O stretching vibration of the photoproduced radicals resulting from the H-atom abstraction from the aldehyde groups.

Tables

Generic image for table
Table I.

Observed IR spectra of anisole isolated in argon and xenon matrices and B3LYP/6-311++G(d,p) calculated wavenumbers (scaled by 0.978) and IR intensities.a

Generic image for table
Table II.

B3LYP/6-311++G(d,p) calculated wavenumbers (scaled by 0.978) and IR intensities for benzene, observed bands for the matrix-isolated compound and bands assigned to this species in the photolysed benzaldehyde matrices.a

Generic image for table
Table III.

B3LYP/6-311++G(d,p) calculated wavenumbers (scaled by 0.978) and IR intensities for the closed-ring ketene isomeric of p-anisaldehyde and observed bands assigned to this species in the photolysed p-anisaldehyde argon matrix.a

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/content/aip/journal/jcp/136/14/10.1063/1.3701734
2012-04-13
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Using heavy atom rare gas matrix to control the reactivity of 4-methoxybenzaldehyde: A comparison with benzaldehyde
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/14/10.1063/1.3701734
10.1063/1.3701734
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