The microwave spectrum of phthalan has been observed in the frequency range of 18-70 GHz. The spectra of the ground and ten excited vibrational states have been assigned and rotational and quartic centrifugal distortion constants have been obtained from semirigid rotor fits to the observed line frequencies. The microwave spectrum is not consistent with either the C2v equilibrium conformation deduced from the far infrared spectrum or the C2 equilibrium conformation obtained from the single vibronic level fluorescence spectra. The microwave data indicates that the bending of the five membered ring is a very anharmonic vibration with a double minimum potential function with a low barrier and that phthalan therefore has a C(s) equilibrium conformation. The previous spectroscopic data can be reinterpreted in a manner consistent with this and gives a barrier height of 38 cm-1. The twisting of the five membered ring is a reasonably harmonic vibration and its fundamental wave-number is approximately 180 cm-1. The microwave data is in agreement with the far infrared assignment of the butterfly vibration in the region 215-220 cm-1.

The conformation and ring-puckering vibration of 2-methyloxetane have been studied using microwave spectroscopy and ab initio computations. The microwave spectra of the ground and first four excited states of the ring-puckering vibration have been observed in the frequency range 8-40 GHz and the rotational and quartic centrifugal distortion constants have been determined. Vibrational energy separations have been obtained from relative intensity measurements. The electric dipole moment (in D) of the ground vibrational state has been determined from Stark effect measurements as mu(a) = 0.0187 (5), mu(b) = 1.852(2), mu(c) = 0.08(3), and mu(t) = 1.854(3). The vibrational energy separations and the vibrational dependence of the rotational constants suggest that the ring-puckering vibration has an asymmetric single minimum potential function and also gave a revised assignment of the far infrared spectrum (J. Mol. Struct. 56 (1979) 157). A combined fit to the rotational constants, vibrational energy separations and far infrared vibrational frequencies has been used to determine a reduced potential for the ring puckering vibration. The partial derivatives of the rotational constants with respect to the reduced ring-puckering coordinate show that the equilibrium conformation has the methyl group in the equatorial position. Ab initio computations of the ring-puckering potential function have been made using 6-31G* orbitals and full geometry optimization. These computations also show the molecule to have an asymmetric single minimum potential function with an equatorial equilibrium conformation.

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Stark effect measurements in trimethylene sulphone have been analysed to give a value of 0.23 D for the μb electric dipole transition moment connecting the v=O and v=1 states of the ring-puckering vibration. The μa component of the electric dipole moment has been determined in the v=0 to v=3 states of this vibration.

Microwave measurements on the ground and first eight excited states of the ring-puckering vibration of butadiene sulfone have been extended to millimeter wavelengths. The microwave spectra of the same vibrational states of α,α′-D4 butadiene sulfone have been observed. For both isotopomers the Coriolis interaction between the v = 0 and v = 1 states has been analyzed to give the energy separation between these two states. These data and the variation of the rotational constants have been used to derive reduced potential functions for the ring-puckering vibration. The barrier to ring inversion is 49(2) cm−1 for butadiene sulfone and 44(2) cm−1 for the α,α′-D4 isotopomer. The ring-puckering vibrational dependence of the quartic centrifugal distortion constants, including a small dependence of ΔJ and δJ, has been accounted for.

ChemInformVolume 21, Issue 40 Physical Organic Chemistry ChemInform Abstract: Ring-Puckering Potential Function for Butadiene Sulfone J. C. LOPEZ, J. C. LOPEZ Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this authorD. G. LISTER, D. G. LISTER Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this authorR. M. VILLAMANAN, R. M. VILLAMANAN Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this authorJ. L. ALONSO, J. L. ALONSO Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this author J. C. LOPEZ, J. C. LOPEZ Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this authorD. G. LISTER, D. G. LISTER Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this authorR. M. VILLAMANAN, R. M. VILLAMANAN Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this authorJ. L. ALONSO, J. L. ALONSO Dep. Quim.-Fis., Fac. Cienc., Univ. Valladolid, E-47005 Valladolid, SpainSearch for more papers by this author First published: October 2, 1990 https://doi.org/10.1002/chin.199040046Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume21, Issue40October 2, 1990 RelatedInformation

The ring puckering in butadiene sulphone has been investigated using microwave spectroscopy and ab initio computations. Microwave spectra of the ground and first eight excited states of the ring-puckering vibration have been observed. A two state analysis of the vibration–rotation interaction for the v=0 and v=1 states gives an energy separation between these states of 4.97 (3) cm−1. This separation and the vibrational dependence of the rotational constants have been used to derive the reduced potential function V(X)=4.7(X4−6.5X2) for the ring-puckering vibration. This potential function gives a barrier to ring inversion of 50 (11) cm−1 and an equilibrium dihedral angle of ≊20°. Ab initio computations using STO 3-21G* orbitals and full geometry optimization give a barrier height of 88 cm−1 and an equilibrium dihedral angle of 19.2°. The ab initio computations predict structural relaxation including a rocking of the sulphone group during the ring-puckering motion. This is supported by calculations of the vibration–rotation interaction parameter (δμac/δQ). The μa component of the electric dipole moment has been determined as 4.6 (1) D from Stark effect measurements. The ab initio computations and Stark effect measurements indicate that the transition moment 〈0‖μc‖1〉 is 1–2 D.

A two-dimensional ring puckering potential energy surface has been derived for ethylene carbonate using ab initio and flexible model computations. The surface is expressed as a mixed Taylor—Fourier series expansion of the generalized ring puckering coordinates (q, φ). The ab initio molecular energies have been used to determine the degree of truncation of the series which gives an accurate representation of the surface in the region of q, φ space spanned by data from microwave spectroscopy. The ab initio geometries have been used for the kinetic energy part of the flexible model computations. By scaling the coefficients of the ab initio potential it is possible to obtain reasonably good agreement with the observed inversion splitting, fundamental puckering vibrational frequencies and most of the variation in the rotational constants with excitation of the ring puckering vibrations. This potential function has a twisted C2 symmetry equilibrium conformation with a puckering amplitude of 27 pm. The lowest energy path to ring inversion passes through the planar ring conformation where there is a barrier of 2.7 kJ mol− (229 cm−1).

The microwave spectrum of 3-methyloxetane has been observed in the frequency range 12.4–40.0 GHz in order to investigate the conformational behaviour of this molecule. The spectra of the ground vibrational state, the first five excited states of the ring-puckering vibration and four other excited vibrational states have been assigned and their rotational and quartic centrifugal distortion constants have been obtained. The ring-puckering vibrational energy separations obtained from microwave relative intensity measurements do not appear to be consistent with those predicted from a ring-puckering potential function obtained from far infrared spectroscopy. A revised assignment of the far infrared spectrum gives a potential function consistent with the microwave relative intensity measurements. This potential function is preferred because of its superior ability to account for the ring-puckering vibrational dependence of the rotational and centrifugal distortion constants. Although this is a slightly asymmetric double minimum potential function, the top of the barrier lies below the lowest vibrational level and therefore in its ground vibrational state 3-methyloxetane effectively has a planar ring. The four excited states which do not belong to the ring-puckering progression based on the ground vibrational state are assigned to a ring-puckering progression based on the first excited state of the methyl torsion. The first two members of this progression show relatively large changes in their rotational constants relative to the ground vibrational state indicating a strong interaction between the ring-puckering and methyl torsion vibrations. The electric dipole moment has been determined from Stark effect measurements as μa = 1.910 (5) D, μc= 0.77 (2) D and μ = 2.06 (1) D for the ground vibrational state. The μa component and the total electric dipole moment decrease with excitation of the ring-puckering vibration.

The conformation of ethyleneurea has been investigated using microwave spectroscopy and ab initio computations. The molecule is found to have a C2 symmetry equilibrium conformation with a non-planar ring and non-planar geometries at the nitrogen atoms. Both the inertial data and ab initio computations show that the amide hydrogen atoms occupy equatorial positions. The observation of inversion splittings on ground vibrational state μa Q-branch lines indicates an inversion barrier of ∼6–8 kJ mol−1. The computed energy difference between the planar ring molecule and the equilibrium conformation is 7.2 kJ mol−1 using a 6.31 G** orbital basis. A second conformer with Cs symmetry is computed to have an energy of 0.2 kJ mol−1 less than that of the planar ring molecule.

ChemInformVolume 18, Issue 35 Preparative Organic Chemistry ChemInform Abstract: Identification of the Pyrolysis Products of Some Aromatic Amines Using Microwave Spectroscopy. R. CERVELLATI, R. CERVELLATI Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorG. CORBELLI, G. CORBELLI Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorA. DEGLI ESPOSTI, A. DEGLI ESPOSTI Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorD. G. LISTER, D. G. LISTER Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorP. E. TODESCO, P. E. TODESCO Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this author R. CERVELLATI, R. CERVELLATI Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorG. CORBELLI, G. CORBELLI Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorA. DEGLI ESPOSTI, A. DEGLI ESPOSTI Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorD. G. LISTER, D. G. LISTER Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this authorP. E. TODESCO, P. E. TODESCO Ist. Spettrosc. Mol., C. N. R., 40126 Bologna, ItalySearch for more papers by this author First published: September 1, 1987 https://doi.org/10.1002/chin.198735097Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue35September 1, 1987 RelatedInformation

ChemInformVolume 19, Issue 17 Physical Organic Chemistry ChemInform Abstract: Large-Amplitude Vibrations and Microwave Band Spectra. Part 1. Adamantan-1-ol. G. CORBELLI, G. CORBELLI Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorA. DEGLI ESPOSTI, A. DEGLI ESPOSTI Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorL. FAVERO, L. FAVERO Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorD. G. LISTER, D. G. LISTER Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorR. CERVELLATI, R. CERVELLATI Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this author G. CORBELLI, G. CORBELLI Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorA. DEGLI ESPOSTI, A. DEGLI ESPOSTI Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorL. FAVERO, L. FAVERO Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorD. G. LISTER, D. G. LISTER Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this authorR. CERVELLATI, R. CERVELLATI Ist. Spettrosc. Mol., CNR, I-40126 Bologna, ItalySearch for more papers by this author First published: April 26, 1988 https://doi.org/10.1002/chin.198817047AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue17April 26, 1988 RelatedInformation

The conformation and ring inversion in ethylene carbonate have been investigated using microwave spectroscopy and ab initio computations. The vibrational satellite spectra of the normal isotopic species of ethylene carbonate and the rotational constants of Bäckvall et al.(Tetrahedron Lett. 1980, 21, 4985) for cis- and trans-[1,2-2H2]ethylene carbonate show the molecule to have a twisted C2 equilibrium conformation. The vibrational satellite spectra have been analysed in terms of independent ring-bending and twisting vibration. A potential function for the twisting vibration derived from the variation of the rotational constants with vibrational state, and vibrational energy separations obtained from relative intensities and Coriolis perturbations give an equilibrium twist angle of 19° and a barrier to ring inversion of 2.8 kJ mol–1. The twist angle has also been obtained from inertial data, and a value of 15° is obtained using two methods of calculation. Ab initio computations of the ring-puckering potential-energy surface have been made using STO-3G and STO-3-21 G orbitals and complete geometry optimization. The STO-3G computations predict a planar C2ν equilibrium geometry, but with the twisting vibration being lower in frequency and more anharmonic than the bending vibration. The STO-3-21G computations predict a C2 conformation with an equilibrium twist angle of 14° and barrier to inversion through the planar ring conformation of 1.1 kJ mol–1. The computed barrier to ring inversion by pseudorotation is 14.3 kJ mol–1.

A re-investigation of the microwave spectra of 2,5- and 2,3-di-hydrothiophene was performed. For the 2,5 isomer lines up to J = 40 were measured for the ground and first five vibrationally excited states of the ring-puckering mode. The centrifugal distortion constants in the ground and excited states show the expected behaviour for a single mininum potential function. For 2,3-dihydrothiophene evidence was found for a Coriolis interaction between the ground vibrational state and the first excited state of the ring-puckering vibration. A preliminary analysis of this effect places the vibrational energy separation ΔE01 at 348 ± 4 MHz.

The microwave spectrum of 2,3-dihydrofuran has been reinvestigated and measurements for the ground and first five excited states of the ring puckering vibration have been extended to higher frequencies and rotational quantum numbers in order to study the vibrational dependence of the rotational and centrifugal distortion constants. The ring puckering potential function derived by Green from the far infrared spectrum does not reproduce the vibrational dependence of the rotational constants well. A slightly different potential function is derived which gives a reasonable fit both to the far infrared spectrum and the rotational constants. This changes the barrier to ring inversion from 1.00 kJ mol−1 to 1.12 kJ mol−1. The vibrational dependence of the centrifugal distortion constants is accounted for satisfactorily by the theory developed by Creswell and Mills. An attempt to reproduce the vibrational dependence of the rotational and centrifugal distortion constants using the ring puckering potential function and a simple model for this vibration has very limited success.

Ab initio computations have been performed on aniline and N-methylaniline using standard STO-3G orbitals to analyze the inversion barrier and the degree of non planarity in the two molecules. Our analysis indicates that the lowering of thei barrier in N-methyl-aniline with respect to aniline is due to hyperconjugation.