Organoisocyanates: the conformational stability determination by infrared, raman and microwave spectroscopy and ab initio calculation
No Thumbnail Available
Authors
Meeting name
Sponsors
Date
Journal Title
Format
Thesis
Subject
Abstract
Conformational stability studies have been carried out for several quasilinear organoisocyanates and organoisothiocyanates. The infrared and Raman spectra in the gaseous, liquid and solid phases have been recorded as well as the variable temperature infrared spectra of the sample compound dissolved in rare gas solution. The complete vibrational assignments have been proposed for all the energetically stable conformations. Microwave spectra for several of the ring molecules have been investigated from 10,000 to 21,000 MHz with transitions for the most stable conformer assigned. For methylisocyanate, the barrier to internal rotation and linearity has been determined to be 46 cm-1 and 975 cm-1, respectively. For the Ethylisocyanate, the cis conformation is determined to be more stable than the trans form by 100 ± 4 cm-1. dimethylsilylisocyanate was determined to have an essentially linear SiNCO moiety. The spectral analyses of Isopropylisothiocyanate indicated one stable conformer (trans) in the annealed solid but in the fluid phases most of the molecules have energies above the barriers of the two predicted bound vibrational states i.e., trans and gauche forms. For dimethylsilylisocyanate, the low wavenumber Raman spectrum of the gas with a significant number of Q-branches for the SiNC(O) bend is consistent with an essentially linear SiNCO moiety. For cyclopropylisocyanate, the enthalpy difference has been determined to be 77 ± 8 cm-1 with the trans form more stable than the cis conformer with 59 ± 2% of the trans form present at ambient temperature. For cyclobutylisocyanate, an enthalpy difference of 131 ± 13 cm-1 was obtained with the equatorial-trans conformer the more stable form. For cyclohexylisocyanate, an enthalpy difference of 397 40 cm-1 was obtained from seven conformer pairs with the equatorial-trans form more stable than the axial-trans conformer. To support the analysis of the vibrational assignment, ab initio and hybrid density functional theory calculations have been carried out. For each molecule, a completed vibrational analysis and potential energy distributions have been proposed. The adjusted r0 structural parameters have been determined for all molecules.
Table of Contents
Introduction -- Theoretical background -- Experimental -- Vibrational spectra and structural parameters of some xnco and xocn (x=h,f,cl,br) molecules -- The r [sub 0] structural parameters, vibrational spectra, ab intio calculations and barriers to internal rotation and linearity of methylisocyanate -- Conformational stability, structural parameters and vibrational assignment from variable temperature infrared spectra of xenon and krypton solutions and ab initio calculations of ethylisocyanate -- Microwave, raman, and infrared spectra, r [sub 0] structural parameters, conformational stability and ab initio calculations of isopropylisocyanate -- Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignment of dimethylsilylisocyanate -- Conformational stability from variable temperature infrared spectra of xenon solutions, r [sub0] structural parameters, ans ab initio calculations of cyclopropylisocyanate -- Microwave, raman, and infrared spectra, r [sub0] structural parameters, conformational stability and ab initio calculations of cyclobutylisocyanate -- Microwave, infrared, and raman spectra, r[sub 0] structural parameters, conformational stability and ab initio calculations of cyclohexylisocyanate
DOI
PubMed ID
Degree
Ph.D.