Ab initio study of fluorocyclobutenes: an attempt to resolve the difference between microwave spectroscopy and electron diffraction geometries of hexafluorocyclobutene

Han, Young‐Kyu; Lee, Yoon Sup; Lee, Sang Yeon; Kim, Jong Taik

doi:10.1016/s0166-1280(97)00074-2

Cited by 14 publications

(15 citation statements)

References 35 publications

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“…Both CC double‐bond lengths are almost equal (C1C2 1.320(3), C3C4 1.318(3) Å), which shows a negligible influence of fluorine substitution on the CC bond lengths, in agreement with our earlier results found for 1,1,2‐trifluorobutadiene49 and the CC bond lengths obtained from low‐temperature X‐ray diffraction of ethane53 and tetrafluoroethene 54. On the basis of ab initio calculations, the CC bond lengths of ethane55 and tetrafluoroethene56 differ by 0.007 Å on the MP2 level of theory with the 6‐31G** basis set.…”

Section: Resultssupporting

confidence: 90%

P254: Lung development in fetal sheep observed with Magnetic Resonance Imaging (MRI) and ultrasound B-scan

Tchirikov

Wedegärtner

Hecher

et al. 2003

Ultrasound Obstet Gynecol

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th World Congress on Ultrasound in Obstetrics and GynecologyPoster abstracts (P = 0.11). The mean duration of sampling was 144 ± 188 sec with a 22 G needle versus 144 ± 120 sec with a 23 G needle (P = 0.99). No significant differences were noted in sampling time between the two needle types. Four of the six operators showed a clear learning curve with shorter sampling times with increasing number of procedures.Conclusion: This experimental study shows that the use of a 23 G echo-tip  needle compared to a 22 G needle was not associated with significantly different procedure duration or defect size, therefore not supporting the claimed advantages of this more expensive needle. Objective: To evaluate whether ultrasound screening during pregnancy increases the ability to stop or reduce smoking. Methods: This multicenter questionnaire study was performed to describe smoking characteristics among pregnant women and evaluate the factors that influence the ability to reduce smoking during pregnancy. The ultrasound screening was examine as one factor. Women were interviewed within 2 days after deliverance in the maternity units on smoking habits before and during pregnancy. Each maternity was visited only once. The study was conducted during May and June 2002 in multiple practices in 4 French regions: Nord-Pas de Calais, Languedoc-Roussillon, HauteNormandie and Ile de France. Only two investigators interviewed consenting patients, both were tabacologists. Results: 979 women delivered were asked to participate. Three hundred three women (31%) were smoking regularly before pregnancy. Nearly all (98%) of them tried to change their smoking habits. More than one third (38.0%) of women reported that ultrasound was a positive tool to enhance motivation to reduce smoking. Ultrasound screening may be a positive factor to reduce smoking. However most women who stop smoking during pregnancy do so in the first trimester (84%) mainly before the first ultrasound exam. Thus, the routine ultrasound scan itself does not seem to influence attitudes to stop smoking any further. Conclusion: Ultrasound screening during pregnancy is a tool which may be included in comprehensive and individualized anti smoking support. P252 P252aOutcome of amniocentesis performed in a Perinatology Unit over 5 years L. Onderoglu, O. Deren, B. Saygan-Karamursel, A. B. Savas-Alparslan, A. Kizilkilic-Parlakgumus, T. Durukan and E. Tuncbilek Hacettepe University Hospital, TurkeyObjective: To investigate the indications, results and fetal loss rates of amniocentesis performed at a Perinatology Unit during 1998-2002. Methods: Amniocentesis records from January 1998 to July 2002 were retrospectively reviewed from a computer based system at the Perinatology Unit. Patient records at the Genetic Unit were reviewed for karyotype results. All of the patients who did not deliver at our hospital were called by telephone to learn about the pregnancy outcome. Results: A total of 1837 amniocentesis procedures were performed. The most common indication was advanced maternal age...

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Section: Resultssupporting

confidence: 90%

P254: Lung development in fetal sheep observed with Magnetic Resonance Imaging (MRI) and ultrasound B-scan

Tchirikov

Wedegärtner

Hecher

et al. 2003

Ultrasound Obstet Gynecol

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“…Electron diffraction results give shorter CC bonds and markedly longer C−C bonds in halocyclobutenes. , This discrepancy is not understood. One recent theoretical study based on DFT methods supports the electron diffraction findings; another supports the spectroscopic results …”

Section: Resultssupporting

confidence: 60%

“…A number of ab initio investigations have been made of these effects. Among these studies are those of Allen and co-workers, Boggs and Fan, Hertwig et al, and Han et al…”

Section: Introductionmentioning

confidence: 99%

Complete Structure of trans-3,4-Difluorocyclobutene from Microwave Spectroscopy

et al. 2002

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Microwave spectra have been observed with Fourier transform and cold jet expansion techniques in the 6−17 GHz range for trans-3,4-difluorocyclobutene, its two 13C1 modifications, two d 1 modifications, and the perdeutero species. Watson-type Hamiltonians have been fit with a full set of quartic centrifugal distortion constants for all species except the d 4 species. Complete structures fit with an r s/r 0 treatment and an r 0 treatment are in satisfactory agreement. Preferred r s/r 0 results with Costain uncertainties in parentheses are 1.349(4) Å for the CC bond, 1.503(9) Å for the contiguous C−C bonds, 1.534(4) Å for the distant C−C bond, 1.398(6) Å for the C−F bond, 1.081(3) Å for the C−H bond, and 1.102(5) Å for the −C−H bond. Consistent with its C 2 symmetry, the ring is slightly puckered, and the C−F bonds are roughly equatorial. Compared with the structure of cyclobutene, the structure of trans-3,4-difluorocyclobutene shows a modest lengthening of the CC bond and more significant decreases in the C−C bond lengths. These effects are consistent with observations for other fluorine-substituted rings in which contiguous fluorine atom substitution causes CC bond shortening and distant fluorine atom substitution causes CC bond lengthening. The CC bond adjustments in trans-3,4-difluorocyclobutene are, however, surprisingly similar to the adjustments observed for 3,3,4,4-tetrafluorocyclobutene.

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“…To evaluate the equilibrium geometries theoretically converged with respect to the size of the basis sets, Han et al carried out geometry optimization on the eclipsed forms of 1,2-difluoroethane with various basis sets, such as 6-31G( d , p ), 6-311G( d , p ), and 6-311++G(2 df ,2 p ). As compared with the 6-31G( d , p ) results, they found that using the 6-311G( d , p ) basis set and appending additional diffuse functions could lengthen the CC bond of 1,2-difluoroethane by 0.005 Å.…”

Section: Computational Detailsmentioning

confidence: 99%

Theoretical Study on the Low-Energy and High-Energy Conformers of the Three Isomers of 1,4-Difluorobutadiene

et al. 2001

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The low-energy and high-energy conformers of the three isomers of 1,4-diflorobutadiene (DFBD) have been investigated with the Gaussian-3 (G3) and G3//B3LYP (G3B3) methods. The geometrical structures of the conformers have been gradient optimized by the HF and B3LYP methods with the 6-31G(d,p) basis set. Natural bond orbital (NBO) analysis has also been performed at the same levels of theory. The computational results show that the high-energy and low-energy conformers of a given isomer is essentially the same in geometry, except that their torsional angles about the C-C bonds are different, and among them only the high-energy conformer of the cis-trans isomer is coplanar. Harmonic vibrational frequency analysis indicates that the high-energy conformers are characterized by their smaller separations of the two CdC stretching modes and the reversed order of the V(CdC) sym and V(CdC) asym peaks compared to that of their low-energy conformer partners. NBO analysis indicates that the π-π* conjugative interaction in a high-energy conformer is smaller than that in its low-energy conformer partner and that the significant n-π* interactions in the high-energy conformers contribute to their extra stabilities. Through the G3B3 calculations, the conformational energies of the cis-cis, cis-trans, and trans-trans isomers are estimated to be 17.1, 7.9, and 9.8 kJ mol -1 , respectively. The stability sequence of the high-energy conformers in different isomers is (cis-trans) > (transtrans) > (cis-cis), while that of the low-energy conformers is (cis-cis) > (cis-trans) > (trans-trans). The distinctive energy relationships between the conformers of different energy groups are attributed to the intramolecular hydrogen bonds in the high-energy conformers.

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Ab initio study of fluorocyclobutenes: an attempt to resolve the difference between microwave spectroscopy and electron diffraction geometries of hexafluorocyclobutene

Cited by 14 publications

References 35 publications

P254: Lung development in fetal sheep observed with Magnetic Resonance Imaging (MRI) and ultrasound B-scan

P254: Lung development in fetal sheep observed with Magnetic Resonance Imaging (MRI) and ultrasound B-scan

Complete Structure of trans-3,4-Difluorocyclobutene from Microwave Spectroscopy

Theoretical Study on the Low-Energy and High-Energy Conformers of the Three Isomers of 1,4-Difluorobutadiene

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