Infrared intensities: cyclohexane. A molecular force field and dipole moment derivatives

Wiberg, Kenneth B.; Walters, Valerie A.; Dailey, William P.

doi:10.1021/ja00303a009

Cited by 42 publications

(31 citation statements)

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“…155,159,160,162,163,[166][167][168][169][170][171][172][173][174][175][176][177] There is a trend of vibrational modes that are blue-shifted with correlation to ring strain in spectra of bulk cycloalkanes, which is similar to the trend observed for silane linked cycloalkanes ( Figure 6C). For four-, five-, and six-membered cycloalkanes, this stretching mode is assigned to an asymmetric C-H stretching motion on the basis of assignments made for bulk spectra, 155,159,160,162,163,[166][167][168][169][170][171][172][173][174] whereas for cylopropane, the blue-shift is so significant that the C-H stretch we observe on the silane surface is assigned as a symmetric stretch because the asymmetric stretch would occur at a frequency higher than the IR light probed in these experiments. 159,160,[175][176][177] Also notable in the silane spectra is the appearance of multiple peaks in the C-H asymmetric and symmetric stretching regions.…”

Section: Cyclic Alkanesmentioning

confidence: 55%

“…The highest two frequency modes, which both have the same phase, are nondegenerate asymmetric methylene stretches, similar to those observed in bulk phase, where they are assigned to coupled motions of multiple methylene groups. 162,166,171 The higher of these modes is blue-shifted from frequencies between 2915 and 2935 cm -1 , where methylene stretches are assigned for cyclohexane in bulk spectra. 155,162,166,171 However, the observation of methylene stretching modes above 2940 cm -1 in cyclohexane is not unprecedented.…”

Section: Cyclic Alkanesmentioning

confidence: 95%

See 1 more Smart Citation

Pentane, Hexane, Cyclopentane, Cyclohexane, 1-Hexene, 1-Pentene,cis-2-Pentene, Cyclohexene, and Cyclopentene at Vapor/α-Alumina and Liquid/α-Alumina Interfaces Studied by Broadband Sum Frequency Generation

2009

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The molecular orientation and structure of adsorbates at oxide interfaces is driven by surface-molecule and molecule-molecule interactions and is useful for predicting reactivity and product selectivity in heterogeneous chemical reactions, including those important in catalytic processes. Using broadband vibrational sum-frequency generation spectroscopy, we probed cyclic and acyclic alkanes and olefins at buried vapor/solid and liquid/ solid interfaces of the R-alumina (0001) surface under ambient conditions. The spectroscopic signatures of the adsorbates were measured and compared with bulk phase spectra and spectra of model surfaces containing hydrocarbons covalently linked to glass slides using silane chemistry. By utilizing appropriate polarization combinations, the orientations of hydrocarbons adsorbed from the vapor were evaluated and compared to the hydrocarbon orientations at the liquid/solid interface. The data support a proposed orientation for n-alkanes and cycloalkanes at the liquid/solid interface in which the hydrocarbons lie with the planes of their carbon backbones parallel to the surface, whereas at the vapor/solid interface, the adsorbates are oriented with their carbon backbones in an orientation neither parallel nor perpendicular to the surface. The surface vibrational spectra of olefins at both types of interfaces indicate that their orientations differ from saturated counterparts, and their unique spectral signatures allow differentiation of adsorbed olefins from alkanes.

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Section: Cyclic Alkanesmentioning

confidence: 55%

Section: Cyclic Alkanesmentioning

confidence: 95%

Pentane, Hexane, Cyclopentane, Cyclohexane, 1-Hexene, 1-Pentene,cis-2-Pentene, Cyclohexene, and Cyclopentene at Vapor/α-Alumina and Liquid/α-Alumina Interfaces Studied by Broadband Sum Frequency Generation

2009

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“…In the case of entry 17, gauche butane, the model predicts that the axial C-H bond of cyclohexane is longer and weaker than the equatorial C-H bond; this is consistent with the 3-21G (3 l), 4-21G (32), and 4-3 1G (33) optimized structures of this molecule. In the calculations of Wiberg et al (33), the axial and equatorial C-H bond lengths of cyclohexane are 1.088 and 1.086 A, respectively. Our values for gauche butane are 1.0883 and 1.0874; the effect of the added methyl group can be seen in the structure found for propane (entry 18), in which the bond lengths are 1.0865 A ("axial") and 1.0857 A ("equatorial").…”

Section: Data Basementioning

confidence: 94%

The Perlin Effect: bond lengths, bond strengths, and the origins of stereoelectronic effects upon one-bond C–H coupling constants

Wolfe¹,

Pinto²,

Varma³

et al. 1990

Can. J. Chem.

152

105

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The magnitude of a one-bond C-H coupling constant depends upon the chemical environment of the hydrogen atom and, especially, upon its stereochemical relationship to vicinal lone electron pairs. However, a lone electron pair is not essential for the observation of a stereoelectronic effect, since even cyclohexane exhibits different axial and equatorial C-H coupling constants. We propose the name "Perlin Effect" to describe such observations. An analysis of the extensive experimental data regarding the Perlin Effect reveals that, in cyclohexane and in six-membered rings having one or more heteroatoms of the first row attached to the carbon of interest, ' J~-~ is always larger for an equatorial hydrogen than for an axial hydrogen. The magnitude of the Perlin Effect is reduced when the carbon carrying the hydrogen of interest is attached to first row and second row atoms or heteroatoms, and it reverses when the carbon atom carries two heteroatoms from below the first row.The existence of the Perlin Effect in nuclear magnetic resonance spectra is reminiscent of an infrared effect known as the Bohlmann bands, whose origin has previously been explained by quantitative perturbational molecular orbital (PMO) theory in terms of the effects of lone electron pairs upon the lengths and strengths and, therefore, the chemical reactivities of vicinal C-H bonds. Since the magnitude of a one-bond C-H coupling constant is expected to vary inversely with bond length, the origins of the Perlin Effect and of the Bohlmann bands would seem to be the same, i.e., the longer (weaker) C-H bond has the smaller one-bond coupling constant. This expectation has now been confirmed: for 25 molecules, representing a total of 35 different kinds of C-H bonds, the bond lengths, stretching force constants, and charge distributions have been determined from fully optimized 6-3 1 G* molecular orbital calculations. In nine of ten cases for which experimental data exist for pairs of diastereomeric or diastereotopic hydrogens, the shorter C-H bond of the pair has the larger coupling constant; in the tenth case, the experimental difference is only 1-2 Hz. Moreover, a global analysis of the data in terms of the equationwhere J is an experimental coupling constant, q is a total atomic charge, and r is a C-H bond length, correlates 23 different types of C-H bonds linearly with a correlation coefficient of 0.9 15. The C parameter is the leading term of the correlation. Among the systems studied theoretically are eight molecules of the type CH3CHXY (Y = OH, SH; X = F, C1, OH, SH), which are representative of systems containing both endocyclic and exocyclic first row and second row anomeric effects. The exocyclic effect is found to be very similar for first row and second row substituents, but the endocyclic effect is larger for the first row substituent. Both findings agree with experimental data in solution. Finally, quantitative PMO analysis has been employed to analyse the origins of the different C-H bond lengths in the various molecules of the study. dans...

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“…1) and, at least to a minor extent, owing to the wavelength dependence of the transmittance of the edge filter, the band occurring at ¾802 cm 1 and originating in the totally symmetric and hence completely polarized (depolarization ratio: < 0.05 57 ) A 1g ring breathing mode 77 (mainly in-phase C-C stretching coordinates 78 ), does not represent the strongest Raman band in our spectrum. This is usually the case in spectra that are excited employing visible laser radiation with a perpendicular orientation of its plane of linear polarization with respect to the scattering plane in right-angle scattering (it is typically 3 times more intense than the neighboring band measured at ca 1028 cm 1 which has been assigned to a E g ring stretching vibration 78 ). 57 -60 However, under rigorously resonant scattering conditions, which usually result in significant enhancement of only polarized Raman bands, a parallel orientation of the plane of linear polarization of the incident radiation should be avoided but, by implementing and appropriately adjusting an additional half-wave plate (vide infra), a perpendicular orientation ought to be used instead.…”

Section: Spectral Resultsmentioning

confidence: 99%

“…This chosen wavenumber calibration standard also provides an excellent opportunity to simultaneously quantify the effective resolution achievable for our DUV Raman measurements. A reasonable estimate for the achievable resolution can be obtained by determining the degree of separation of the two Raman bands observed at ca 2925 and 2937 cm 1 in the C-H stretch region of the cyclohexane spectrum forming a nice doublet ideally suited for resolution testing purposes (the 2925 cm 1 band is associated with a doubly degenerate E g mode predominantly composed of axial and equatorial C-H stretching coordinates, 78 whereas the 2937 cm 1 band originates in a totally symmetric A 1g mode mainly consisting of in-phase equatorial C-H stretching coordinates 78 ). From visual comparison of the general spectral appearance of this cyclohexane doublet measured using DUV excitation at 257 nm, as displayed in the inset of Fig.…”

Section: Spectral Resultsmentioning

confidence: 99%

A new single grating spectrograph for ultraviolet Raman scattering studies

Hecht

Clarkson

Smith

et al. 2005

J Raman Spectroscopy

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A state-of-the-art single grating spectrograph for Raman scattering studies within the deep ultraviolet (DUV) region of the electromagnetic spectrum is discussed. It is based on a high throughput DUV version of a single-stage monochromator originally designed for use in the visible spectral region. Its key components are two identical, newly designed calcium fluoride camera lenses each consisting of five different individual optical elements. The first of these lenses collimates the Raman scattered DUV radiation entering the spectrometer through its entrance slit. The second lens focuses the collimated beam of dispersed Raman scattered DUV radiation emerging from a high-resolution reflection grating onto a charge coupled device (CCD) detector with enhanced DUV sensitivity. A novel high transmission edge filter is used as a blocking device for a sufficient rejection of the Rayleigh line generating a relatively sharp transmittance cutoff at a Stokes Raman wavenumber shift of about ∼450 cm −1 employing 257 nm DUV excitation. Overall, this new spectrograph enables rapid collection of Stokes DUV Raman scattered photons at f /2 wide apertures with sufficiently large signal-to-noise ratios (SNRs) in relatively short acquisition times and with an effective spectral resolution of approximately ∼6 cm −1 . Backscattered Raman spectra of the following chemicals are presented as typical results illustrating the excellent performance characteristics of this new DUV spectrograph for a variety of experimental conditions within different scattering scenarios and for a relatively wide range of commonly used sample preparation techniques: neat cyclohexane, laboratory air, polycrystalline D-glucose, single crystal L-alanine and a dilute aqueous solution of 2 -deoxyadenosine.

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Infrared intensities: cyclohexane. A molecular force field and dipole moment derivatives

Cited by 42 publications

References 0 publications

Pentane, Hexane, Cyclopentane, Cyclohexane, 1-Hexene, 1-Pentene,cis-2-Pentene, Cyclohexene, and Cyclopentene at Vapor/α-Alumina and Liquid/α-Alumina Interfaces Studied by Broadband Sum Frequency Generation

Pentane, Hexane, Cyclopentane, Cyclohexane, 1-Hexene, 1-Pentene,cis-2-Pentene, Cyclohexene, and Cyclopentene at Vapor/α-Alumina and Liquid/α-Alumina Interfaces Studied by Broadband Sum Frequency Generation

The Perlin Effect: bond lengths, bond strengths, and the origins of stereoelectronic effects upon one-bond C–H coupling constants

A new single grating spectrograph for ultraviolet Raman scattering studies

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