Data for "The Enol of Isobutyric Acid"

Abstract

Spectra for deuterated and non-deuterated enols, along with density functional theory computations IR and UVVis-spectra. A Sumitomo cryostat system consisting of an RDK 408D2 closed-cycle refrigerator cold head and an F-70 compressor unit was used for matrix isolation experiments. A polished CsI window was mounted in the cold head sample holder. The sample holder, connected with silicon diodes for temperature measurements, was covered by a vacuum shroud, which was equipped with KBr windows to allow for IR measurements. In some experiments BaF2 windows were used due to their higher transparency when measuring UV/vis spectra. The sample and the host gas (Ar, purity of 99.999%) were co-deposited at 3.5 K. All spectral data were collected at 3.5 K. The pyrolysis zone was equipped with a heatable 90 mm long quartz tube (inner diameter 7 mm), controlled by a Ni/CrNi thermocouple. The travel distance of the sample from the pyrolysis zone to the matrix was ∼45 mm. Ar was stored in a 2 L gas balloon, which was evacuated and filled three times before every experiment. The sample was evaporated from a Schlenk tube at 80 °C (water) and reduced pressure (∼3 × 10–6 mbar) and co-deposited with a high excess of argon on both sides of the matrix window in the dark (preventing unwanted photochemistry) at a rate of ∼1 mbar min–1, based on the pressure inside the Ar balloon. Pyrolyses were carried out at 750 °C. IR spectra were recorded between 7000 and 350 cm–1 with a resolution of 0.7 cm–1 with a Bruker Vertex 70 FTIR spectrometer. A spectrum of the cold matrix window before deposition was used as background spectrum for the subsequent IR measurements. UV/vis spectra were recorded between 190 and 800 nm with a resolution of 1 nm with a Jasco V-760 spectrophotometer. A high-pressure-mercury lamp equipped with a monochromator (LOT Quantum Design) or a low-pressure-mercury lamp (Gräntzel) fitted with a Vycor filter were used for irradiation of the matrix during photochemical experiments. Spectra were saved as "X-files" and can be opened with "OPUS". Computations. All DFT computations were performed with the Gaussian 16,1 Revision C.01 (full citations for electronic structure codes are given at the end of this document) at the B3LYP/def2-TZVP2-3 level of theory. The keywords Opt and Freq=NoRaman were used for the characterization of minima on the PES. For transition structures the keyword Opt=(ts,tight,calcfc,noeigen) was used. UV/Vis absorptions were computed by using the keyword td(50-50,nstates=10). The results of the calculations were saved as "out" files and can be opened with the editor and graphically with 'ChemCraft'.