Rotational Spectrum of 1,1,1-Trifluoro-2-butanone Using Chirped-Pulse Fourier Transform Microwave Spectroscopy

Abstract

The pure rotational spectra of 1,1,1-trifluoro-2-butanone and its four (13)C isotopologues have been studied using the new chirped-pulsed Fourier transform microwave spectrometer at the University of Manitoba in combination with a conventional Balle-Flygare-type instrument. Quantum chemical calculations, at the MP2/6-311++G(d,p) level, were carried out to obtain information about the structure, relative stability, and difference in populations of the three lowest energy conformers corresponding to dihedral angles of 0°, 82.8°, and 119.2° along the carbon backbone. The observed spectra are that of conformer I (dihedral angle 0°), and, based on analysis of the observed splitting, the V(3) barrier to internal rotation of the methyl group has been determined to be 9.380(5) kJ mol(-1). The spectroscopic constants of the five isotopologues were used to precisely derive the r(s) and partial r(0) geometries of this conformer based on an assumed planar carbon backbone (as supported by the spectra and ab initio calculations).

Investigation of structural trends in difluoropyridine rings using chirped-pulse Fourier transform microwave spectroscopy and ab initio calculations

“…The pure rotational spectra of the parent, 13 C and 15 N isotopologues were first recorded using our broadband chirped pulse Fourier transform microwave (cp-FTMW) instrument which has been previously described [11]. Survey spectra were measured in 2 GHz windows between 8-14 GHz and the observed transitions had linewidths of $200 kHz FWHM when individual FIDs were acquired for 20 ls.…”

Targeting the Rich Conformational Landscape of N‐Allylmethylamine Using Rotational Spectroscopy and Quantum Mechanical Calculations

“…The rotational spectrum of AMA was collected using a chirped pulse and a cavitybased Balle-Flygare type Fourier transform microwave spectrometer, which were described in detail previously. [28,29] Initially, the broadband cp-FTMW spectrum was recorded from 8-18 GHz in segments of 2 GHz from which the most intense rotational transitions due to different conformers of AMA were identified. Later, to collect transitions at higher frequencies and to resolve the hyperfine structure due to the N quadrupolar nucleus, final frequency measurements were performed using the BF-FTMW instrument from 8-22 GHz which provides higher resolution and sensitivity.…”

“…Given that the sample is a liquid at room temperature with a relatively low boiling point (61–62 °C), a gas mixture containing 1 % of the title compound in neon (100 kPa) was prepared at room temperature and expanded into the high vacuum chamber of the spectrometers using a pulsed nozzle (1 mm diameter orifice) to create a supersonic jet. The rotational spectrum of AMA was collected using a chirped pulse and a cavity‐based Balle‐Flygare type Fourier transform microwave spectrometer, which were described in detail previously [28,29] . Initially, the broadband cp‐FTMW spectrum was recorded from 8–18 GHz in segments of 2 GHz from which the most intense rotational transitions due to different conformers of AMA were identified.…”

Understanding (coupled) large amplitude motions: the interplay of microwave spectroscopy, spectral modeling, and quantum chemistry

“…This is an important feature for assignments of the spectra and for conformational analysis. With all of these advantages, CP-FTMW is the spectrometer of choice for many scientists worldwide and has been equipped in almost all microwave spectroscopic labs [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59].…”