Vibrational Overtone Spectroscopy of Cycloheptatriene

Abstract

The spectrum of the first through fifth vibrational overtone absorptions of cycloheptatriene is reported. The spectrum for the first and second overtones was recorded using a liquid sample, while the third, fourth, and fifth overtones were recorded for gaseous samples. A method is developed using the correlation between ab initio CH bond lengths and the local mode transition energy to predict the experimental spectra for the third, fourth, and fifth vibrational overtone spectra. These predictions were used to assign the absorption peaks for the "boat" conformer of cycloheptatriene in the gaseous spectrum. Progressions belonging to the olefinic and methylenic CH bond stretches are identified for both the gaseous and liquid data.

Vibrational Overtone Spectroscopy of Cycloheptatriene Chromium Tricarbonyl, Benzene Chromium Tricarbonyl, and Corresponding Hydrocarbon Ligands

“…The overtone spectrum of free CHT was analyzed in our previous work . The most intense transition at 11 366 cm -1 and high-energy shoulder of this peak (11 437 cm -1 ) were assigned to the two different types of CH olefinic oscillators: CH 2,3,4,5 and CH 1,6 .…”

“…b Taken from ref . c Our previous work (ref ). d Data for cycloheptatriene tungsten tricarbonyl taken from: King, R. B.; Fronzaglia, A. Inorg.…”

Vibrational Overtone Spectroscopy of Cycloheptatriene-d6 at the Third and Fourth Overtone Regions

“…At the third overtone the absence of the olefinic CH bond stretch absorptions in the CHT- d 6 spectrum around 11 300−11 400 cm -1 leaves only two well-resolved peaks associated with the methylenic CH bonds of the CHT- d 6 ring (Figure ). Based on the general pattern reported for the CH methylenic bond in cyclic hydrocarbons ( r CH ax > r CH eq ) and ab initio geometry optimization for CHT, the lower energy peak at 11 096 cm -1 can be assigned to the CH ax of CHT- d 6 , while the higher energy transition, located at 11 215 cm -1 , belongs to the CH eq . Similar arguments can be made for the two peaks recorded in the next overtone region (Figure ), where the CH ax peak appeared at 13 643 cm -1 and the CH eq transition appeared at 13 785 cm -1 .…”

“…In a previous report the vibrational overtone spectrum of gaseous cycloheptatriene (CHT) was presented. The main absorption features at the third and fourth overtones were assigned to the CH olefinic oscillators of CHT using a direct correlation method.…”

“…Then the CHT-d 6 sample (91%) was collected using preparative gas chromatography.The third and fourth overtone spectra of CHT-d 6 were obtained using the photoacoustic spectrometer described previously. 1 The sample pressure was 14 Torr, and 300 Torr of argon was added to increase the photoacoustic signal.The spectra of CHT-d 6 and CHT at the third and fourth overtone regions are shown in Figures 1 and 2, respectively. Peak positions and vibrational assignments are tabulated in Table 1.…”