Ring-puckering Potential Function Research Articles

Calculation of kinetic energy functions for the ring-puckering vibration of asymmetric five-membered rings

The use of vectors simplifies the representation of the molecular structures resulting from the ring puckering of asymmetric five-membered rings. The kinetic energy (inverse reduced mass) functions have been calculated for several ring molecules including 2,3-dihydrofuran, 2,3-dihydrothiophene, 2-cyclopenten-1-one, and 2-phospholene. The structures used for the calculations were determined from molecular mechanics calculations. The accurate determination of the kinetic energy terms has made it possible to calculate the one-dimensional ring-puckering potential functions for these molecules in dimensional form.

Centrifugal distortion and the ring puckering vibration in the microwave spectrum of 2,3-dihydrofuran

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.

The 330-nm S1- S0 electronic spectrum of 1-pyrazoline: Probable hindered pseudorotation in S1 and confirmation of the ring-puckering potential function in S0 by single vibronic level fluorescence spectroscopy

The S 1- S 0 absorption spectrum of 1-pyrazoline is rotationally sharp but vibrationally extremely irregular, and other techniques are necessary to aid its assignment. The relaxed fluorescence spectrum shows a very long progression in the NN twisting vibration, suggesting that the ring is twisted in S 1 whereas, in S 0, this part of the ring is planar but the CH 2 group in position 4 is puckered. With a twisted ring in S 1 it seems likely that the NN twisting and CH 2(4) puckering modes in S 0 should be combined and newly described as radial and hindered pseudorotational modes in S 1. The vibronic transitions accompanying such an S 1- S 0 electronic transition are derived. Single vibronic level fluorescence spectra from many vibronic levels of S 1 show progressions in both the NN twisting and CH 2(4) puckering vibrations in S 0, but only with Δ v even. This strongly supports the suggestion that these two modes are heavily mixed in S 1, and indicates that the fluorescing states are either above the barrier to pseudorotation or not far below it, so that there is appreciable tunnelling through the barrier. The progressions in the CH 2(4) puckering vibration allow us to assign uniquely the puckering quantum number, in S 0, of the band in which excitation took place. In addition, the spacings in these progressions further confirm the preferred potential function derived from the far-infrared spectrum and confirmed previously from the microwave spectrum.

ChemInform Abstract: CONFORMATIONAL STUDY OF MOLECULES WITH ASYMMETRIC ISOTOPIC SUBSTITUTION. RING PUCKERING OF 1‐SILACYCLOBUTANE‐1‐D

1-Silacyclobutane-1-d/sub 1/ has been prepared and its infrared spectra have been analyzed. Several ring-puckering transitions have been observed in the far-infrared region and sum and difference bands have been observed in the Si-H stretching region. A ring-puckering potential function which simultaneously fits the data for the D/sub 0/, d/sub 1/, and d/sub 2/ isotopic forms has been determined. Calculation of the wave functions for the d/sub 1/ molecule shows that each of the lowest two very nearly degenergy states (nu = 0 and nu = 1) corresponds to only one distinct molecular conformation. Similarly, the nearly degenerate nu = 2 and nu = 3 states are primarily restricted to specific conformations. Doublets observed for the Si-H and Si-D stretching bands, corresponding to stretches from equitorial or axial positions, confirm these calculations. Model calculations on related systems demonstrate that both a sufficiently large barrier height and an asymmetry of the kinetic energy expansions are necessary for the conformational separation according to vibrational states. Although the reduced masses of the two conformers of 1-silacyclobutane-1-d/sub 1/ differ by only 0.20%, this is enough to produce the observed conformational discrimination.

Conformational study of molecules with asymmetric isotopic substitution. Ring puckering of 1-silacyclobutane-1-d

1-Silacyclobutane-1-d/sub 1/ has been prepared and its infrared spectra have been analyzed. Several ring-puckering transitions have been observed in the far-infrared region and sum and difference bands have been observed in the Si-H stretching region. A ring-puckering potential function which simultaneously fits the data for the D/sub 0/, d/sub 1/, and d/sub 2/ isotopic forms has been determined. Calculation of the wave functions for the d/sub 1/ molecule shows that each of the lowest two very nearly degenergy states (nu = 0 and nu = 1) corresponds to only one distinct molecular conformation. Similarly, the nearly degenerate nu = 2 and nu = 3 states are primarily restricted to specific conformations. Doublets observed for the Si-H and Si-D stretching bands, corresponding to stretches from equitorial or axial positions, confirm these calculations. Model calculations on related systems demonstrate that both a sufficiently large barrier height and an asymmetry of the kinetic energy expansions are necessary for the conformational separation according to vibrational states. Although the reduced masses of the two conformers of 1-silacyclobutane-1-d/sub 1/ differ by only 0.20%, this is enough to produce the observed conformational discrimination.

ChemInform Abstract: THE RING PUCKERING POTENTIAL FUNCTION OF TRIMETHYLENE SULFIDE AND TRIMETHYLENE SELENIDE

Chemischer InformationsdienstVolume 12, Issue 19 Physical Organic Chemistry ChemInform Abstract: THE RING PUCKERING POTENTIAL FUNCTION OF TRIMETHYLENE SULFIDE AND TRIMETHYLENE SELENIDE J. L. POUSA, J. L. POUSASearch for more papers by this authorO. M. SORARRAIN, O. M. SORARRAINSearch for more papers by this authorJ. MARANON, J. MARANONSearch for more papers by this author J. L. POUSA, J. L. POUSASearch for more papers by this authorO. M. SORARRAIN, O. M. SORARRAINSearch for more papers by this authorJ. MARANON, J. MARANONSearch for more papers by this author First published: May 12, 1981 https://doi.org/10.1002/chin.198119070AboutPDF 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. Volume12, Issue19May 12, 1981 RelatedInformation

ChemInform Abstract: THE FAR‐INFRARED SPECTRA AND RING PUCKERING POTENTIAL FUNCTIONS OF SEVERAL DEUTERATED ANALOGS OF TRIMETHYLENE SULFIDE

Chemischer InformationsdienstVolume 5, Issue 33 Physical Organic Chemistry ChemInform Abstract: THE FAR-INFRARED SPECTRA AND RING PUCKERING POTENTIAL FUNCTIONS OF SEVERAL DEUTERATED ANALOGS OF TRIMETHYLENE SULFIDE H. WIESER, H. WIESERSearch for more papers by this authorJ. A. DUCKETT, J. A. DUCKETTSearch for more papers by this authorR. A. KYDD, R. A. KYDDSearch for more papers by this author H. WIESER, H. WIESERSearch for more papers by this authorJ. A. DUCKETT, J. A. DUCKETTSearch for more papers by this authorR. A. KYDD, R. A. KYDDSearch for more papers by this author First published: August 20, 1974 https://doi.org/10.1002/chin.197433066AboutPDF 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. Volume5, Issue33August 20, 1974 RelatedInformation

Interpretation of the vibrational spectra of small ring systems II. Perfluorocyclobutane

The vibrational spectra of gaseous and solid perfluorocyclobutane have been interpreted in terms of a planar molecule with D4h symmetry in view of the observed mutual exclusion between the infrared and Raman frequencies. A vibrational assignment for perfluorocyclobutane is presented and based upon the observed infrared and Raman band contours, depolarization ratios, relative band intensities, and positions. A comparison of the ring-puckering potential functions and skeletal structures of cyclobutane, 1,1-difluorocyclobutane, trimethylene oxide, and 3,3-difluoroxetane suggests the inversion barrier is reduced significantly upon introduction of a CF2 group in the cyclic systems. The apparent trend toward planarity appears to continue in 1,1,2,2-tetrafluorocyclobutane and perfluorocyclobutane. The factors that may dictate the equilibrium structures of small ring molecules are considered in view of the data presently available.

The far-infrared spectra and ring puckering potential functions of several deuterated analogs of trimethylene sulfide

The far-infrared spectra in the region of 50–200 cm −1 of several deuterated analogs of trimethylene sulfide (viz α- d 2, β- d 2, α, α′- d 4 and d 6) are reported. The bands are assigned to ring puckering transitions. The potential constants in the function, V( Z) = A( Z 4 + BZ 2), Z the reduced puckering coordinate, were determined for each compound separately. The barrier height, AB 2 4 , is found to vary upon isotopic substitution in the quadratic-quartic approximation.

Raman spectra of gases. VIII. Ring puckering in diborane

The Raman spectra of gaseous 11B2H6, 10B2H6, and B2D6 have been recorded from 0–3000 cm−1. The ν = 0 → 2, ν = 1 → 3, and ν = 2 → 4 ring puckering transitions have been observed for the 11B2H6 isotopic species at 753.7, 776.1, and 795.6 cm−1, respectively. The ν = 0 → 2 ring puckering transitions of the 10B2H6 and B2D6 species have been observed at 756.6 and 531.0 cm−1, respectively. The least squares fit of these data yields the ring puckering potential function V(X) = 6.50 × 105X4 + 7.30 × 104X2. The intensity of the Δν = 2 ring puckering transitions is shown to be due to electrical anharmonicity rather than mechanical anharmonicity or Fermi resonance. The observed gerade fundamentals are found to agree reasonably well with those found earlier from Raman investigations of the liquids.

Ring puckering potential functions for normal and deuterated trimethylene oxides

Calculations of the potential function for the ring-puckering vibration of trimethylene oxide and four deuterated derivatives have been carried out. It was found that although the spectrum of each molecule could be reproduced by using a mixed quadratic-quartic function, no one function would fit all of the molecules. Barrier heights were found to lie between the values of 15.1 ± 0.5 cm −1 for the normal molecule and 11.2 ± 0.5 cm −1 for the perdeuterated molecule.

Microwave Spectrum, Ring-Puckering Potential Function, and Dipole Moment of 3,3-Difluoroxetane

The microwave spectrum of 3,3-difluoroxetane has been observed and assignments made of the rotational constants for the ground state and for six excited states of the ring-puckering vibration. From the rotational constant variation, intensity information, and inertial defect considerations it is concluded that the molecule is planar in the ground state with zero barrier to the ring-puckering motion. The ring-puckering potential function is given by V (X)=ν0(X4+7.0 X2). The dipole moment is directed along the a axis and has a value of 0.40±0.01 D.

Far-Infrared Spectra and the Ring-Puckering Potential Function of Silacyclopent-3-ene and Silacyclopent-3-ene-1,1-d2

A series of a far-infrared absorption bands have been observed between 35 and 100 cm−1 in the spectra of silacyclopent-3-ene, CH2CH=CHCH2SiH2, and silacyclopent-3-ene-1,1-d2. These absorptions result from the transitions between the various energy levels of the ring-puckering vibration. The frequencies of the bands can be calculated quite accurately using a pure quartic potential, V = 14.34Z4 for the hydride and V = 13.20Z4 for the deuteride where Z is the ring-puckering coordinate in reduced form. A slightly better fit for each spectrum is obtained by adding a small positive quadratic term to the potential function. The ring-puckering potential for this molecule shows that the structure of the five-membered ring is a planar one and that it has no barrier to inversion like that in cyclopentene. This lack of a potential barrier is attributed to a smaller barrier to internal rotation in the –CH2–SiH2– bond as compared to –CH2–CH2–. Also there is evidence from the isotope shift of the frequencies (which is related to the reduced masses of the 2 isotopic species) that the distance between the silicon atom and the double bond is much smaller than expected. This suggests that a weak bond between the Si d orbitals and the π system is partly responsible for the planarity of the compound.

Microwave Spectrum, Ring-Puckering Potential Function, and Dipole Moment of Methylenecyclobutane

The microwave spectra of methylenecyclobutane in the ground state and in the first six excited states of the ring-puckering vibration have been assigned. The υ = 0 state and υ = 1 state are very close in energy and are strongly coupled giving rise to nonrigid-rotor spectra. Analysis shows the energy difference to be 33 592 MHz. This energy difference together with the vibrational dependence of the rotational constants gives the ring-puckering potential function to be 7.65(X4 − 9.15X2) cm−1 where X is a reduced ring-puckering coordinate. This potential function contains a barrier to ring inversion of 160 ± 40 cm−1. The a component of the dipole moment is found to be 0.514 D in the ground state and to have the ring-puckering vibrational dependence μa = 0.496 + 0.0051 〈X2〉υυ (debye).

Microwave Spectrum, Ring-Puckering Potential Function, Ring Structure, and Dipole Moment of Cyclobutanone

The microwave spectrum of cyclobutanone in the ground state and the first 10 excited states of the ring-puckering vibration has been assigned. Most features of the observed variation of rotational constants with ring-puckering state and of the far-infrared spectrum are accounted for with the ring-puckering potential function V(Z) = ν0[12Z2 + 0.4918Z4 + 1.598 exp(−1.0Z2)], with ν0 = 29.85 cm−1. Z is a dimensionless coordinate for the ring-puckering motion. A barrier of 7.6 ± 2 cm− exists at the planar ring conformation; with the υ = 0 level lying 9.2 cm−1 above the top of the barrier. A perturbation of the υ = 8 state is discussed. The ground-state rotational spectra of the three 13C monosubstituted species have also been assigned and the structure of the ring determined. With the carbonyl carbon labeled C1 and other carbons numbered sequentially around the ring, the ring structural parameters are r(C1C2) = 1.527 + 0.003 Å, r(C2C3) = 1.556 ± 0.001 Å, ∠C2C1C2′ = 93.1 ± 0.3°, ∠C1C2C3 = 88.0 ± 0.3°, ∠C2C3C2′ = 90.9 ± 0.2°. Stark-effect measurements have yielded a value of 2.89 ± 0.03 D for the dipole moment of the common isotopic species in the ground vibrational state.

Far-Infrared Spectra of Ring Compounds. II. The Spectrum and Ring-Puckering Potential Function of Cyclopentene

The infrared spectrum of cyclopentene has been recorded in the range 18–300 cm−1. Two series of thirteen and nine Q branches, respectively, were observed, both of which arise from the strongly anharmonic energy levels of the B1 ring-puckering vibration. The longer, more intense series is assigned to molecules in the ground vibrational state of all the other vibrations, and the shorter, weaker series to molecules in the first excited state of the A2 ring-twisting vibration. Each set of Q branches can be fitted to transitions between the energy levels of a double-minimum potential function of the form V=a(x4—bx2), where x is the B1 ring-puckering coordinate. The height of the barrier opposing planarity is calculated to be 232±5 cm−1, and the equilibrium angle between the two dihedral planes of the puckered ring to be 23.3°±1°.

Microwave Spectrum, Dipole Moment, and Ring-Puckering Vibration of Vinylene Carbonate

The microwave spectrum of vinylene carbonate has been studied in the frequency region between 12 000 and 26 500 Mc/sec. Rotational constants and moments of inertia have been derived for the vibrational ground state and for the first three excited states of the ring-puckering vibrational mode. The molecule is planar, with no barrier at the planar configuration in the ring-puckering potential function. Measured intensities of the vibrational satellites are fitted well by a purely quadratic potential function. The dipole moment, which lies exclusively along the a axis, is 4.57±0.05 D.