Microwave spectra and centrifugal distortion constants of oxetane

Creswell, R. A.; Mills, Ian

doi:10.1016/0022-2852(74)90188-x

Cited by 70 publications

(28 citation statements)

References 20 publications

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“…The interconversion between the two equivalent methyl groups, by means of a tunneling effect, yields a single 13 C signal in the spectrum with doubled intensity (Figure a). For such a potential, the Coriolis coupling interactions between the rotational levels of different vibrational states are reflected in abnormally high centrifugal distortion constant values, which present a characteristic zig‐zag variation with the vibrational quantum number . In the Supporting Information (Tables S5–S8) we show how this double‐minimum potential function is causing the unusual centrifugal distortion effects, which reproduces a double‐minimum potential function with a barrier of 157 cm −1 .…”

Section: Resultsmentioning

confidence: 99%

The Shape of the Simplest Non‐proteinogenic Amino Acid α‐Aminoisobutyric Acid (Aib)

Alonso

Peña

López

et al. 2019

Chemistry A European J

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The simplest non‐proteinogenic amino acid α‐aminoisobutyric acid (Aib), an analogue of glycine and alanine, has been vaporized by laser ablation and probed by high‐resolution Fourier transform microwave spectroscopic techniques. Comparison of the experimental rotational and 14N nuclear quadrupole constants with that predicted ab initio has allowed the identification of three conformers of Aib exhibiting three types of hydrogen‐bond interactions I (NH⋅⋅⋅O=C, cis‐COOH), II (OH⋅⋅⋅N, trans‐COOH), and III (N−H⋅⋅⋅O−H, cis‐COOH) within the amino acid backbone. The observation of conformer III, not detected previously for related proteinogenic amino acids with a nonpolar side chain in a supersonic expansion, indicates that the presence of the methyl groups should restrict the conformational relaxation from conformer Aib‐III to Aib‐I. For conformer Aib‐II, the rotational spectra of the 13C isotopomers reveal a tunneling motion arising from the two equivalent methyl groups in the molecule. The observation of a single spectrum at the midpoint between those predicted for the two 13C of the methyl groups has been explained by considering a double‐minimum potential function with a low‐energy interconversion barrier for a large amplitude internal motion. This singular fact has been corroborated by the anomalous centrifugal distortion effects determined in conformer Aib‐II.

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Section: Resultsmentioning

confidence: 99%

The Shape of the Simplest Non‐proteinogenic Amino Acid α‐Aminoisobutyric Acid (Aib)

Alonso

Peña

López

et al. 2019

Chemistry A European J

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“…Comparing equation (5) series of isotopically substituted oxetans, Creswell and Mills [11] and Mallinson and Robiette [12] have exploited this parameter to derive information about the dynamics of the puckering motion. We plan a similar analysis also for the related thietans.…”

Section: Fitting and Spectrummentioning

confidence: 99%

“…VIBRATIONAL DEPENDENCE OF THE CENTRIFUGAL DISTORTION CONSTANTSBecause of the anharmonic nature of the puckering potential function, the coupling term in (2) will cause an interaction between any pair of puckering levels provided one is even and the other odd. The weak interaction between well separated levels contribute to the observed vibrational dependence of the quartic distortion constants, and these contributions may be calculated by adapting the method of Creswell and Mills[11]. A second order perturbation treatment of the interaction terms in the I I z A-reduction which we have used gives(As) ~ = As* , ( Aj~:)v = Aj~*--(h'/Zh)(,h,a~/IaL) ~ 0~, ( A~:)~ = AK* + (h4/2h )(a,,=/ Uc)' 0~, (~J).…”

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confidence: 99%

The microwave spectrum of thietan-2,2,4,4-d₄

1980

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The microwave spectrum for thietan-2,2,4,4-d4 is analysed in six of its lowest puckering states and up to J=25. The close lying pairs of states of vp= 0/1, 2/3 and 4/5 are treated with a vibration-rotation hamiltonian which includes an off-diagonal coupling term in vp. Additional corrections to this coupling term in higher powers of the angular momentum operator are derived and their importance for improving the fit of calculated to observed data is tested. The variation of the centrifugal distortion constants with vp follows the model of Creswell and Mills (1974, ft. rnolec. Spectrosc., 52, 392). A value is determined for the derivative with respect to the puckering coordinate of the ac-component of the inverse moment of inertia tensor.

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“…The spectra of the £ Å 0 and £ Å 1 states of 2,3-dihydro-The partial derivatives in these equations were calculated to furan has been fitted to a two-state Hamiltonian, be (Ìm ac /ÌX ) X Å0 Å 30. £ Å 0 and £ Å 1, respectively, DE is the vibrational energy difference between both states, and the coupling term is [4] where the P a are the corresponding angular momentum operators and the coupling constants F ac and F bc can be related to the partial derivatives of the off-diagonal of the inverse coupling tensor, m, with respect to the ring-puckering coordinate (14), by MHz from a Creswell and Mills (4) type fit of the constants Pickett (15). Very good fits are obtained when some sextic constants are included.…”

Section: Table 1 Rotational and Centrifugal Distortion Constants Obtamentioning

confidence: 99%

“…For the ground vibrational low 46 GHz (1,2). The vibrational dependence of the rota-state R-branch lines up to J Å 23 and Q-branch lines up to tional constants and the Watson (3,4) centrifugal distortion J Å 53 have been measured. constants D JK , D K , and d K was found to be consistent with the The observed millimeter-wave frequencies have been fitdouble minimum potential function for this vibration (2), as ted, together with the previously measured centimeter-wave established from previous infrared studies (5,6).…”

Section: Introductionmentioning

confidence: 99%