The Raman spectra of the cylophanes

Scudder, Paul H.; Boekelheide, V.; Cornutt, David; Hopf, Henning

doi:10.1016/0584-8539(81)80115-8

Cited by 12 publications

(34 citation statements)

References 31 publications

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“…For many years 1 was assumed to adopt a totally eclipsed conformation so that it exhibited D 2 h symmetry. ,,,, Early X-ray crystal structures supported this concept. − Even after extensive refinement suggested instead a slightly twisted orientation, calculations of electronic properties of 1 still utilized the D 2 h conformation . Two independent groups, using Hartree−Fock calculations with STO-3G and 3-21G basis sets, deliberately sought the D 2 twisted structure without success. , Their calculations repeatedly converged at the D 2 h geometry.…”

Section: Molecular Geometrymentioning

confidence: 99%

“…Also as a result of the short bridges, the bridgehead atoms of the benzene rings are bent out of the planes of the remaining carbons. The close spacing and distortion of the benzene rings result in interesting effects on the UV and photoelectron spectra, which have been examined in some detail. ,− An early study, however, concluded that the vibrational spectrum is not significantly affected by the distortions or inter-ring interactions . Previous calculations of the properties of [2.2]paracyclophane have focused on the UV excitation spectrum and relative ordering of molecular orbitals as predicted by various semiempirical methods. ,,− Up until very recently, the most sophisticated computational efforts only included single-point calculations using the X-ray crystal structure with D 2 h symmetry; however, two recent papers include Hartree−Fock type geometry optimizations of 1 with STO-3G and 3-21G basis sets …”

Section: Introductionmentioning

confidence: 99%

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Distinctive Normal Harmonic Vibrations of [2.2]Paracyclophane

Walden

Glatzhofer

1997

J. Phys. Chem. A

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The hybrid Hartree−Fock/density functional method B3LYP and 4-31G(d) basis set were used for geometry optimizations and vibrational analysis of both the D2 and D 2 h conformers of [2.2]paracyclophane. The unprecedented full geometry optimization with a split valence basis set and a method that includes electron correlation shows the equilibrium structure of [2.2]paracyclophane to be the twisted D 2 conformation with a calculated twist angle (CringCbridgeCbridgeCring) of 3.9°. We present the first complete assignment of all 90 normal harmonic vibrations of [2.2]paracyclophane. Upon examination of the calculated normal modes and comparison with prior assignments for paracyclophanes and p-xylene, we have identified vibrations that are cyclophane specific modes. Our calculated harmonic frequencies and relative intensities are in excellent overall agreement with the experimental IR spectrum. We have thus demonstrated the potential of hybrid Hartree−Fock/density functional theory as an electron-correlated method suitable and practical for characterizing even the large, highly strained, structurally and electronically unique parent of the [2.2]paracyclophane family.

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Section: Molecular Geometrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Distinctive Normal Harmonic Vibrations of [2.2]Paracyclophane

Walden

Glatzhofer

1997

J. Phys. Chem. A

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“…Since its discovery [2.2]paracyclophane has stimulated considerable spectroscopic − and theoretical interest, − motivated by its unusual electronic structure. Until recently, most spectroscopic assignments were carried out on the basis of a D 2 h molecular symmetry.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study on the Molecular Distortions in [2.2]Paracyclophane and Cyclobutane

Henseler

Hohlneicher

1998

J. Phys. Chem. A

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Unrestricted geometry optimizations on [2.2]paracyclophane and cyclobutane at the MP2/6-31G(d) level led to significant ring distortions in agreement with experimental results. The MP2 method proved most successful in the study of the ring puckering of cyclobutane where various theoretical methods and basis sets were compared. Frequency calculations on [2.2]paracyclophane at the D 2 minimum and at the D 2 h saddle point demonstrate the influence of the molecular twist on the vibrational spectra. The two distorted minima are separated by a C 2 h symmetric barrier of 2.5 kJ/mol. Possible causes for the ring deformation in [2.2]paracyclophane are discussed.

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“…Despite this, there have been reports dealing with a twist angle in the low‐temperature phase declaring the ground state or minimum structure to be of D 2 or D 2 h symmetry 7. 12, 13, 21…”

mentioning

confidence: 99%

“…Earlier spectroscopic studies (IR, Raman) on paracyclophane very often failed to obtain spectra of high accuracy, especially in the low‐energy region of a few hundred wavenumbers 13. 16, 17, 21…”

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confidence: 99%

Direct Spectroscopic Evidence of the Mechanism behind the Phase Transition of [2,2]‐Paracyclophane

Wolf

Lock

Parker

2015

Chemistry A European J

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[2,2]-Paracyclophane undergoes phase transitions at 45 and 60 K. Based on simultaneous Raman spectroscopy and inelastic neutron scattering experiments (12-70 K), it was shown that a twisting motion of the ethylene bridge perpendicular to the plane of the aromatic rings drives the phase transition. The low-temperature (<45 K) and high-temperature (>60 K) conformers only differ by this twisting motion, which freezes out below 45 K and is thermally averaged above 60 K. Between 45 and 60 K, the system gains energy until the phase transition is complete.

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The Raman spectra of the cylophanes

Cited by 12 publications

References 31 publications

Distinctive Normal Harmonic Vibrations of [2.2]Paracyclophane

Distinctive Normal Harmonic Vibrations of [2.2]Paracyclophane

Theoretical Study on the Molecular Distortions in [2.2]Paracyclophane and Cyclobutane

Direct Spectroscopic Evidence of the Mechanism behind the Phase Transition of [2,2]‐Paracyclophane

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