The Conformational Landscape, Internal Rotation, and Structure of 1,3,5-Trisilapentane using Broadband Rotational Spectroscopy and Quantum Chemical Calculations

Abstract

The rotational spectrum of 1,3,5-trisilapentane was observed on a chirped-pulse Fourier transform microwave spectrometer and is reported. During assignment, multiple conformations of the molecule were identified in the molecular beam. Prior quantum-chemical calculations performed on the molecule show that the identified spectra correspond to the lowest three calculated energetic structures. These structures are of C 2 (Conf.1), C 2v (Conf.2), and C 1 (Conf.3) symmetry, with relative energy ordering of Conf.1 < Conf.3 < Conf.2, which is in stark contrast to n-pentane and all known silicon-substituted n-pentane derivatives. This is found to most likely arise from the elongation of the Si−C bond and the size of the silicon atoms providing for the C 2 and C 1 structures relieving steric hindrance in comparison to that of the C 2v . In the C 2v and C 1 conformers, splitting in the spectra due to internal rotation of the −SiH 3 end groups of 1,3,5-trisilapentane was observed and determined. The C 2v equivalent V 3 values are 368.46(33) cm −1 , and the C 1 V 3 values are 347.78(21) and 360.18(88) cm −1 , respectively. These barriers are compared to similar species in order to help verify their veracity and are determined to be accurate based on similar molecular silyl rotors.

Structure, Stability, and Spectroscopic Properties of Small Acetonitrile Cation Clusters

“…In order to explore a lower limit for the errors in the spectrum simulations, the experimental spectroscopic constants were employed to simulate an empirical spectrum. For low J values ( J max = 10), the average frequency displacement was around 0.012 MHz, in accordance with previous works where this empirical approach was used (e.g., refs and ). Moreover, following the strategy described in the work of Puzzarini, we computed empirical parameters for CH 3 CN, scaled by using the experimental/theoretical ratio obtained with both measured and calculated values of the rotational constant B .…”

Rotational spectroscopy of methyl tert-butyl ether with a new Ka band chirped-pulse Fourier transform microwave spectrometer

“…In addition, the intrinsically narrow Doppler widths achievable at low frequency allows for resolution of small splittings arising from large-amplitude motion and intramolecular interactions. [2][3][4][5][6][7][8] CP techniques are routinely used to study systems of fundamental interest such as clusters, [9][10][11][12] radicals, 13 and astrochemically-relevant species, 14 often in conjunction with a high-resolution, narrow-bandwidth cavity FTMW spectrometer in the centimeter band. In such investigations, the CP spectrum of the system of interest is directly compared against a predicted spectrum from quantum chemical calculations to yield a quick initial fit of experimental spectroscopic constants, followed by targeted measurements with a cavity instrument to explore small splittings as needed.…”

Rotational Spectrum and Ring Structures of Silacyclohex-2-ene and 1,1-Difluorosilacyclohex-2-ene

“…In recent years, the authors have undertaken rotational spectroscopy studies that investigate the structural differences in substituting a carbon with a silicon atom. − Studies of these systems have led to interesting physiochemical results like ring-puckering motions, planar vs nonplanar ring structures, or C 2 symmetry in straight-chain alkane species where one may expect C 2 v . In some of these systems, the potential energy surfaces of the ring-puckering motion may be flatter at the base through the puckering coordinate than the carbon analogues or may result in a double well.…”