Ring-puckering Potential Energy Function Research Articles

Anomeric Effect in Five-Membered Ring Molecules: Comparison of Theoretical Computations and Experimental Spectroscopic Results.

As demonstrated in previous spectroscopic studies of 1,3-dioxole [ J. Am. Chem. Soc., 1993, 115, 12132-12136] and 1,3-benzodioxole [ J. Am. Chem. Soc., 1999, 121, 5056-5062], analysis of the ring-puckering potential energy function (PEF) of a "pseudo-four-membered ring" molecule can provide insight into understanding the magnitude of the anomeric effect. In the present study, high-level CCSD/cc-pVTZ and somewhat lower-level MP2/cc-pVTZ ab initio computations have been utilized to calculate the PEFs for 1,3-dioxole and 1,3-benzodioxole and 10 related molecules containing sulfur and selenium atoms and possessing the anomeric effect. The potential energy parameters derived for the PEFs directly provide a comparison of the relative magnitudes of the anomeric effect for molecules possessing OCO, OCS, OCSe, SCS, SCSe, and SeCSe linkages. The torsional potential energies produced by the anomeric effect for these linkages were estimated to range from 5.97 to 1.91 kcal/mol. The ab initio calculations also yielded the structural parameters, barriers to planarity, and ring-puckering angles for each of the 12 molecules studied. Based on the refined structural parameters for 1,3-dioxole and 1,3-benzodioxole, improved PEFs for these molecules were also calculated. The calculations also support the conclusion that the relatively low barrier to planarity of 1,3-benzodioxole results from competitive interactions between its benzene ring and the oxygen atom p orbitals.

Theoretical Calculations, Microwave Spectroscopy, and Ring-Puckering Vibrations of 1,1-Dihalosilacyclopent-2-enes

High level theoretical CCSD/cc-pVTZ computations have been carried out to calculate the structures and ring-puckering potential energy functions (PEFs) for 1,1-difluorosilacyclopent-2-ene (2SiCPF2) and 1,1-dichlorosilacyclopent-2-ene (2SiCPCl2). The structure and PEF for 1,1-dibromosilacyclopent-2-ene (2SiCPBr2) was obtained by ab initio MP2/cc-pVTZ computations. The parent silacyclopent-2-ene (2SiCP) is puckered with a 49 cm-1 barrier to planarity, 2SiCPF2 has a planar ring system, 2SiCPCl2 has a calculated tiny 4 cm-1 barrier but is essentially planar, and the dibromide has a calculated barrier of 36 cm-1. Microwave spectra of seven isotopic species of 2SiCPF2 were recorded on a chirped pulse, Fourier transform microwave (CP-FTMW) spectrometer in the 6-18 GHz region. The a-type and b-type transitions were observed. The rotational constants and three quartic centrifugal distortion constants were determined for the parent, 29Si, 30Si, and all singly-substituted 13C isotopologues in natural abundance. This allowed for the determination of the heavy-atom structure of the ring and showed the ring to be planar. The experimentally determined rotational constants and geometrical parameters agree very well with the theoretical values and confirm the planarity of the five-membered ring. A comparison of the PEFs for the silane and the three dihalides shows the silane to have the stiffest puckering motion and the dibromide to be the least rigid.

Ring-puckering potential energy functions for cyclobutane and related molecules based on refined kinetic energy expansions and theoretical calculations

With the aid of ab initio calculations, the one-dimensional representations of the ring-puckering vibrations of several four-membered ring molecules have been refined. These one-dimensional models include contributions from MH2 (M = C, Si, Ge) rocking motions and utilize the computed parameter ω which reflects the relative amounts of ring angle bendings. This model leads to much more accurate determinations of the coordinate dependent kinetic energy expressions g44(x) which in turn allow much more accurate calculations of the ring-puckering potential energy functions (PEFs) based on experimental data. The resulting experimental PEFs agree remarkably well with the theoretical functions determined from ab initio calculations. For each molecule spectroscopic data were fit very well utilizing the refined kinetic energy functions and two term PEFs. They were fit even better using three term PEFs including x6 terms. The PEFs, barrier heights, and energy minima are presented for each of these molecules and their isotopic species.

Theoretical Study of Structures and Ring-Puckering Potential Energy Functions of Bicylo[3.1.0]hexane and Related Molecules.

Ab initio computations using the MP2/cc-pVTZ method have been carried out to calculate the structures and relative energies of the different conformations of five bicyclic molecules including bicyclo[3.1.0]hexane, 3-oxabicyclo[3.1.0]hexane, 6-oxabicyclo[3.1.0]hexane, 3,6-oxabicyclo[3.1.0]hexane, and bicyclo[3.1.0]hexan-3-one. Theoretical ring-puckering potential energy functions (PEFs) in terms of the ring-puckering coordinate have been calculated for each of the molecules and these were compared to those determined experimentally from spectroscopic data. Each potential function is asymmetric and has an energy minimum corresponding to where the five-membered ring is puckered in the same direction as the attached three-membered ring. In contrast to the experimental result, the calculations predict that bicyclo[3.1.0]hexane has a second shallow energy minimum. All of the other molecules have a single conformational minimum and their experimental and theoretical PEFs agree very well. The wave functions for the lower ring-puckering energy levels have been computed.

Ring-Puckering Potential Energy Functions for Trimethylene Sulfide and Its Monovalent Cation.

The spectra and ring-puckering potential energy function for trimethylene sulfide cation (TMS+) from vacuum ultraviolet mass-analyzed threshold ionization spectra have recently been reported. To provide an in-depth comparison of the potential function with that of trimethylene sulfide (TMS) itself, we have used ab initio MP2/cc-pVTZ calculations and DFT B3LYP/cc-pVTZ calculations to predict the structures of both TMS and TMS+ and then used these to calculate coordinate-dependent ring-puckering kinetic energy functions for both species. These kinetic energy functions allowed us to calculate refined potential energy functions of the puckering for both molecules based on the previously published spectra. TMS has an experimental barrier of 271 cm-1 and energy minima at ring-puckering angles of ±29°. For TMS+ the barrier is 60 cm-1 and the energy minima correspond to ring-puckering angles of ±21°. The lower barrier for the cation reflects the smaller amount of angle strain in the ring angles for TMS+.

Infrared, Raman, and Ultraviolet Absorption Spectra and Theoretical Calculations and Structure of 2,6-Difluoropyridine in Its Ground and Excited Electronic States

The infrared and Raman spectra of 2,6-difluoropyridine (26DFPy) along with ab initio and DFT computations have been used to assign the vibrations of the molecule in its S0 electronic ground state and to calculate its structure. The ultraviolet absorption spectrum showed the electronic transition to the S1(π,π*) state to be at 37,820.2 cm(-1). With the aid of ab initio computations the vibrational frequencies for this excited state were also determined. TD-B3LYP and CASSCF computations for the excited states were carried out to calculate the structures for the S1(π,π*) and S2(n,π*) excited states. The CASSCF results predict that the S1(π,π*) state is planar and that the S2(n,π*) state has a barrier to planarity of 256 cm(-1). The TD-B3LYP computations predict a barrier of 124 cm(-1) for the S1(π,π*) state, but the experimental results support the planar structure. Hypothetical models for the ring-puckering potential energy function were calculated for both electronic excited states to show the predicted quantum states. The changes in the vibrational frequencies in the two excited states reflect the weaker π bonding within the pyridine ring.

Further insights on the molecular structure, vibrational spectra and ring-puckering potentials of silacyclopent-3-ene and its 1,1-dihalo derivatives: Ab initio and DFT study

The structure, ring-puckering potential energy functions and vibrational spectra of silacyclopent-3-ene (3SCP) and its 1,1-d2 (3SCP-d2), 1,1-difluoro (3SCP-F2), 1,1-dichloro (3SCP-Cl2) and 1,1-dibromo (3SCP-Br2) derivatives were investigated using ab initio MP2 and MP4(SDQ), and BLYP, B3LYP and BB1K density functional calculations. The stable form of 3SCP was obtained from MP4(SDQ) and BB1K levels to be unpuckered with a modest nonplanarity character in excellent agreement with previous experimental results. The 3SCP-F2 ring was predicted by all levels of theory to be the most rigid in the series, while the dichloro and dibromo analogs were predicted to maintain a slightly puckered structure with very small barrier height in terms of the puckering motion. When compared with the results obtained from the MP4(SDQ) theory with the 6-311G(d,p), 6-311+G(d,p) and 6-311++G(d,p) basis sets, the BB1K functional showed noticeable performance over B3LYP and MP2 methods in predicting reliable ring-puckering angle and barrier for all members of the 3SCP series. The infrared and Raman spectra of the investigated cyclic organosilanes were revisited on the basis of the frequencies calculated at B3LYP and BB1K levels and the derived potential energy distribution values.

Vibrational Spectra, Ab Initio Calculations, and Ring-Puckering Potential Energy Function for γ-Crotonolactone

The infrared and Raman spectra of liquid and vapor gamma-crotonolactone have been collected. Both the experimental data and ab initio calculations show that the molecule is rigidly planar in its electronic ground state. This conclusion agrees with the previously reported microwave studies and is attributed to the conjugation between the C=C and C=O double bonds of the ring. The ring-puckering potential energy function was generated from ab initio calculations and was confirmed by the vapor-phase Raman spectra to be nearly harmonic. Density functional theory (DFT) calculations predict a harmonic ring-puckering frequency of 203 cm(-1) as compared to the observed vapor-phase Raman value of 208 cm(-1). The DFT calculations were also used to compute the infrared and Raman spectra of gamma-crotonolactone, and these agree very well with the experimental spectra.

The ring-puckering potential energy function and theoretical calculations for silacyclopent-2-ene-d 0 and 1,1-d 2 and the difluoro and dichloro derivatives

High level ab initio and DFT calculations have been carried out for silacyclopent-2-ene and its 1,1-d 2, 1,1-difluoro, and 1,1-dichloro derivatives. The previously published far-infrared spectra of the ring-puckering vibration, which had been interpreted to be characteristic of a rigid planar molecule, have been reanalyzed for the hydride and 1,1-d 2 derivative. Both the spectra and the theoretical calculations show the molecule to have a small barrier to planarity. The experimental data analyzed with a Gaussian barrier produce a barrier of 49 cm −1 as compared to a value of 47 cm −1 computed using the CCSD/6-311++G(d,p) basis set. The experimental value for the deuteride was determined to be 41 cm −1 from the one-dimensional approximation. All MP2 and DFT computations for the 1,1-difluoro derivative predict a planar structure whereas the MP2 computation when used with triple- ζ basis set predicts a barrier of 13 cm −1 for the chloride. Vibrational frequencies were also computed for these molecules and compared to experimental results for the characteristic frequencies for these types of molecules.

Fluorescence and ultraviolet absorption spectra and structure of coumaran and its ring-puckering potential energy function in the S1(π,π*) excited state

The fluorescence excitation (jet cooled), single vibrational level fluorescence, and the ultraviolet absorption spectra of coumaran associated with its S1(pi,pi*) electronic excited state have been recorded and analyzed. The assignment of more than 70 transitions has allowed a detailed energy map of both the S0 and S1 states of the ring-puckering (nu45) vibration to be determined in the excited states of nine other vibrations, including the ring-flapping (nu43) and ring-twisting (nu44) vibrations. Despite some interaction with nu43 and nu44, a one-dimensional potential energy function for the ring puckering very nicely predicts the experimentally determined energy level spacings. In the S1(pi,pi*) state coumaran is quasiplanar with a barrier to planarity of 34 cm(-1) and with energy minima at puckering angles of +/-14 degrees. The corresponding ground state (S0) values are 154 cm(-1) and +/-25 degrees . As is the case with the related molecules indan, phthalan, and 1,3-benzodioxole, the angle strain in the five-membered ring increases upon the pi-->pi* transition within the benzene ring and this increases the rigidity of the attached ring. Theoretical calculations predict the expected increases of the carbon-carbon bond lengths of the benzene ring in S1, and they predict a barrier of 21 cm(-1) for this state. The bond length increases at the bridgehead carbon-carbon bond upon electron excitation to the S1(pi,pi*) state give rise to angle changes which result in greater angle strain and a nearly planar molecule.

Intermolecular hydrogen bond in molecules with large amplitude motions: rotational spectrum of the complex 3,3-dimethyloxetane⋯hydrogen fluoride

The rotational spectrum of the complex 3,3-dimethyloxetane...HF generated in a supersonic jet has been analyzed using molecular beam Fourier transform microwave spectroscopy in the frequency range 6-18 GHz. Only the axial conformer of the complex has been detected. The parent and 13C and 18O monosubstituted isotopic species were observed both for isolated 3,3-dimethyloxetane and the complex in their natural abundances. For 3,3-dimethyloxetane the methyl group carbon atoms have been observed to be equivalent despite the fact that the ring-puckering potential energy function is of the double minimum type with the ground vibrational state lying below the barrier. An effective (r0) structure of the adduct has been derived from the spectroscopic constants. A C(s) symmetry has been established with HF forming an axial hydrogen bond to the O atom of the ring molecule. No significant structural changes have been observed in 3,3-dimethyloxetane upon complexation. The non-observation of a plausible equatorial conformer is discussed with the help of ab initio computations.

Far-infrared spectrum and ab initio calculations for vinylene carbonate

The far-infrared spectrum of vinylene carbonate shows five closely spaced bands near 233cm−1, characteristic of a nearly harmonic ring-puckering potential energy function. Using a coordinate dependent kinetic energy expansion, the potential energy function was determined to be V(cm−1)=1.652×105x2−1.416×105x4 where x is the puckering coordinate in Å. This shows the molecule to be much more rigid than the similar 3-cyclopenten-1-one due to π bonding interactions involving the oxygen atoms adjacent to the carbonyl group. Ab initio calculations with a B3LYP/6-311++G∗∗ basis set yield structural data in good agreement with the previous microwave work and also predict vibrational frequencies that correspond closely to the experimental values.

Vibrational spectra and conformations of 1,4-cyclohexadiene and its oxygen analogues: ab initio and density functional calculations

The vibrational spectra and ring-puckering potential energy functions of 1,4-cyclohexadiene, 4H-pyran and 1,4-dioxin have been examined using a density functional theory (DFT) method as well as the Hartree–Fock (HF) and second-order Møller–Plesset (MP2) methods. The calculated vibrational frequencies and potential energy functions of those molecules have been compared with previously reported experimental data and MM3 results. For all three molecules, the DFT method using Becke's three-parameter functional (B3LYP) has led to the prediction of more accurate vibrational frequencies than the HF and MP2 methods. The enlargement of the basis set at the B3LYP levels has improved the accuracy of calculated vibrational frequencies. In particular, the C–O–CC torsional force field parameters obtained from the B3LYP method have correctly predicted the ring-puckering potential energy functions of the oxygen-containing analogues, 4H-pyran and 1,4-dioxin, which could not be done by the MM3 method.

Jet-cooled fluorescence excitation spectrum, carbonyl wagging, and ring-puckering potential energy functions of 3-cyclopenten-1-one in its S1(n,π*) electronic excited state

The jet-cooled fluorescence excitation spectrum of 3-cyclopenten-1-one has been recorded in the 308–330 nm region, and the electronic origin for the S1(n,π*) state of A2 symmetry was observed at 30 229 cm−1. The observed spectrum consists of more than 80 bands involving primarily ν3 (carbonyl stretch), ν29 (carbonyl out-of-plane wagging), and ν30 (ring puckering). Bands were also assigned to combinations with seven other vibrational modes. The energies for the v=0 to 11 quantum states of ν29 were measured and used to determine a one-dimensional potential energy function. This function has energy minima at wagging angles of ±24° and a barrier to inversion of 939 cm−1. Four bands associated with ν30 were observed and were used to determine an asymmetric single-minimum one-dimensional ring-puckering potential energy function for the S1(n,π*) state. The ring-puckering energy levels in the ν29 vibrational excited states are little changed from the v=0 state indicating that there is little interaction between the carbonyl wagging and the ring-puckering motions.

The millimetre-wave spectrum of trimethylene sulphide Vibration-rotation coupling between thev=2 andv=3 ring-puckering excited states

The microwave spectra of trimethylene sulphide in the ground and the first eight excited states of the ring-puckering vibration have been measured in the frequency region 26·5‥–250 GHz. Very large Coriolis coupling interaction effects have been observed for the high-J spectra of the v=2 and 3 ring-puckering states in addition to those previously observed between the states v=0 and v=1. A two-state vibration-rotation interaction analysis of these effects has allowed the determination of a vibrational energy spacing ΔE 23=11·97304(1) cm−1. The ring-puckering potential energy function for this molecule has been determined from a simultaneous weighted least-squares fit of the rotational constants and vibrational energy intervals. The observed ring-puckering dependence of the quartic centrifugal distortion constants, including a small dependence of Δ J and δ J , is well accounted for in terms of the ring-puckering potential function obtained in this work.

Jet-cooled fluorescence excitation spectra and carbonyl wagging and ring-puckering potential energy functions of cyclobutanone and its 2,2,4,4-d4 isotopomer in the S1(n,π*) electronic excited state

The jet-cooled fluorescence excitation spectra of cyclobutanone and its 2,2,4,4-d4 isotopomer have been recorded in the 305–335 nm region. The electronic band origin of the d0 molecule for the S1(n,π*) state of A2 symmetry occurs at 30 292 cm−1 (30 265 cm−1 for the d4 molecule). The observed spectra consisting of more than 50 bands for each isotopomer involve ν7, ν8, and ν9 (the three A1 ring vibrations) as well as ν20(C=O in-plane wag), ν26 (C=O out-of-plane wag), and ν27 (ring puckering). Five bands associated with the excited vibrational states of ν26 in the S1(n,π*) electronic state were observed for each isotopic species, and these were used to determine the one-dimensional potential energy functions for the C=O out-of-plane wagging. The C=O wagging angle was determined to be 39° and the barrier to inversion is 2149 cm−1 (2188 cm−1 for the deuteride). For the ring-puckering in the S1 state the lowest three vibrational energy spacings were found to be 106, 166, and 185 cm−1 as compared to values of 35, 57, and 65 cm−1 in the S0 ground state. Several ring-puckering potential energy functions with varying degrees of asymmetry are capable of reproducing the observed results. In all cases, however, the v=0 puckering state lies above any barrier to planarity. A two-dimensional potential function which fits the observed data was also determined in terms of the wagging and puckering coordinates.

Low-frequency vibrational spectra and ring-puckering potential energy function of 1,3-dioxole. A convincing demonstration of the anomeric effect

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLow-frequency vibrational spectra and ring-puckering potential energy function of 1,3-dioxole. A convincing demonstration of the anomeric effectE. Cortez, R. Verastegui, J. Villarreal, and J. LaaneCite this: J. Am. Chem. Soc. 1993, 115, 25, 12132–12136Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://doi.org/10.1021/ja00078a060RIGHTS & PERMISSIONSArticle Views128Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (500 KB) Get e-Alerts Get e-Alerts

Origin of the ring-puckering potential energy function for four-membered rings and spiro compounds: a possibility for pseudorotation

Origin of the ring-puckering potential energy function for four-membered rings and spiro compounds: a possibility for pseudorotation

Vibrational spectra, ring-puckering potential energy function, and conformation of 1,3-disilacyclopent-4-ene

Vibrational spectra, ring-puckering potential energy function, and conformation of 1,3-disilacyclopent-4-ene

Ring-puckering potential energy function and unusual rigidity of silacyclopent-2-ene [Erratum to document cited in CA109(5):37878n

Ring-puckering potential energy function and unusual rigidity of silacyclopent-2-ene [Erratum to document cited in CA109(5):37878n