Structure and UV-induced photochemistry of 2-furaldehyde dimethylhydrazone isolated in rare gas matrices.
In this work, a combined matrix isolation FTIR and theoretical DFT(B3LYP)/6-311++G(d,p) study of 2-furaldehyde dimethylhydrazone (2FDH) was performed. According to calculations, two E and two Z conformers exist, the E forms having considerably lower energy than the Z forms. The absence of relevant sterical hindrance between the two substituents around the CN bond (dimethylamino and 2-furyl) in the E structures and an extended π-p electron delocalization in the hydrazone moiety determines the higher stability of these species relatively to the Z structures. In the lowest energy form (E-AG) the O-C-CN and CN-N-Lp (Lp=lone electron pair of amine nitrogen atom) dihedral angles are predicted by the calculations to be -177.2° and 93.7°, respectively. The weak (NC)-H⋯O hydrogen bond type interaction (H⋯O distance: 252.2 pm) in form E-AG, together with the absence in this form of the destabilizing interaction between the lone electron pairs of the oxygen and nitrogen atoms existing in E-SG, explains its lower energy in comparison with this latter form. Both E-AG and E-SG conformers could be trapped from room temperature gas phase in low temperature argon and xenon matrices. The high E-SG→E-AG energy barrier (>25 kJ mol(-1)) explains that, upon increasing the temperature of the matrices no conformational isomerization could be observed. After irradiation of 2FDH with UV-light at λ>328 and λ>234 nm, two different photochemistries were observed. Irradiation at lower energy (λ>328nm) induced the E-AG→E-SG isomerization. Further irradiation at higher energy (λ>234 nm) led to a quick consumption of 2FDH and production of furan and dimethylisocyanide.
Unidad Académica de Física de la Universidad Autónoma de Zacatecas, Zacatecas, Mexico.
C
C
Araujo-Andrade
B M
BM
Giuliano
A
A
Gómez-Zavaglia
R
R
Fausto
D001128:Argon / Q000737:chemistry*; D005662:Furaldehyde / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification; D006835:Hydrazones / Q000737:chemistry* / Q000302:isolation & purification*; D008968:Molecular Conformation; D055668:Photochemical Processes / Q000528:radiation effects*; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D014466:Ultraviolet Rays; D014978:Xenon / Q000737:chemistry*
D006835:Hydrazones; C067108:2-furaldehyde dimethylhydrazone; D014978:Xenon; D001128:Argon; D005662:Furaldehyde