Molecular Orbital Constrained Electron Diffraction Research Articles

Gas-phase structure and conformation of diethyl ketone studied by molecular orbital constrained electron diffraction

The molecular structure and conformation of diethyl ketone (3-pentanone), C(3)H 3C(2)H 2C(1)OC(4)H 2C(5)H 3, at 27°C were studied by gas electron diffraction (GED). Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Structural constraints were obtained from RHF/6-31G∗ ab initio calculations. Diffraction data were reproduced best by a mixture of two conformers, trans-trans (TT, dihedral angles ф 1(C 4C 1C 2C 3) = ф 2(C 2C 1C 4C 5) = 180°) and trans-gauche (TG). The structural parameters of the TT form determined by GED, with error estimates (3σ) in parentheses, are: r g (CO) = 1.217(2)Å, r g (C 1−C) = 1.519(1)Å, r g (C 2−C 3) = 1.524(1)Å, 〈 r g (C−H〉 = 1.103(3)Å, ∠ α CC(O)C = 116.0(6)°, ∠ α C(O)CC = 114.2(6)°, ∠ α C(O)CH = 108.2(7)°, and 〈∠ α C 2C 3H〉 = 111.4(7)°, where 〈 〉 denotes average value. The difference between r(C 1−C) and r(C 2−C 3) was assumed. Similarly ∠C(O)CH and ∠C 2C 3H were refined in groups. The structural differences between the TT and TG conformers were taken from the 6–31G∗ calculations except for the dihedral angles. The dihedral angles of the TG form were determined to be ф 1 = 61(7)° and ф 2 = 151(14)° . The relative abundances of the TT and TG conformers are 50(10) and 50%, respectively.

Gas-phase structure and conformation of diethyl ketone studied by molecular orbital constrained electron diffraction

The molecular structure and conformation of diethyl ketone (3-pentanone), C(3)H 3C(2)H 2C(1)OC(4)H 2C(5)H 3, at 27°C were studied by gas electron diffraction (GED). Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Structural constraints were obtained from RHF/6-31G∗ ab initio calculations. Diffraction data were reproduced best by a mixture of two conformers, trans-trans (TT, dihedral angles F 1(C 4C 1C 2C 3) = F 2(C 2C 1C 4C 5) = 180°) and trans-gauche (TG). The structural parameters of the TT form determined by GED, with error estimates (3σ) in parentheses, are: r g( CO) = 1.217(2) A ̊ , r g( C 1C ) = 1.519(1) A ̊ , r g( C 2C 3 ) = 1.524(1) A ̊ , 〈r g( CH)〉 = 1.103(3) A ̊ , ∠ α CC(O)C = 116.0(6)°, ∠ α C(O)CC = 114.2(6)°, ∠ α C(O)CH = 108.2(7)°, and 〈∠ α C 2C 3H 〉 = 111.4(7)° , where 〈 〉 denotes average value. The difference between r (C 1C) and r(C 2 3) was assumed. Similarly ∠C(O)CH and ∠C 2C 3H were refined in groups. The structural differences between the TT and TG conformers were taken from the 6–31G∗ calculations except for the dihedral angles. The dihedral angles of the TG form were determined to be F 1 = 61(7)° and F 2 = 151(14)°. The relative abundances of the TT and TG conformers are 50(10) and 50%, respectively.

Molecular orbital constrained gas electron diffraction study of N-acetyl N′-methyl alanine amide

Gas electron diffraction (GED) data were recorded at about 510 K for , N-acetyl N′-methyl alanine amide (ALA) and analysed using the Molecular Orbital Constrained Electron Diffraction procedure. The HF/6-31G * geometries of seven conformations were optimized (C 7 eq ( 1), C 5 ( 2), β 2 ( 3), C 7 ax ( 4), α R ( 5), α L ( 6), and α′ ( 7) and used as constraints of the GED data analysis. HF/6-31G * force constants were determined for each conformation and used to calculate mean amplitudes of vibration and shrinkage corrections. It is found that, in the case of ALA, the customarily applied linear approximation for calculating shrinkages yields values which are unacceptably large. Therefore data analyses were performed both without shrinkage and with shrinkages calculated at a lower temperature. Subject to the selected constraints our interpretation of the GED data supports the following conclusions for vapors of ALA at about 500 K: ( 1) the compound exists in a conformational equilibrium with several significantly populated states; ( 2) the C 5 form is not less populated than the global energy minimum, C 7 eq: ( 3) the helical form, α R, is not a significantly populated conformer.

ChemInform Abstract: Structural and Conformational Analysis of Diethyl Ether by Molecular Orbital Constrained Electron Diffraction Combined with Microwave Spectroscopic Data.

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Structural and conformational analysis of diethyl ether by molecular orbital constrained electron diffraction combined with microwave spectroscopic data

The molecular structure and conformation of diethyl ether, C(3)H 3C(2)H 2O(1)C(4)H 2C(5)H 3, at 27°C was studied by a joint analysis of gas electron diffraction and microwave spectroscopic data. Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Ab initio geometry optimization at the HF/4-21G level was performed on four possible conformers and the results were used as structural constraints. Diffraction and vibrational spectroscopic data are consistent with the presence of two conformers, trans-trans (TT, dihedral angles φ 1(C 4O 1C 2C 3) = φ 2(C 2O 1C 4C 5) = 180°) and trans-gauche (TG), in the vapor phase. The compositions of the TT and TG conformers were determined to be 69(8) and 31%, respectively, by the joint analysis. The structural parameters of the TT form determined are r g(OC) = 1.419(1) Å, r g(CC) = 1.514(2) Å, 〈 r g(CH)〉 = 1.114(2) Å, ∠ αCOC = 113.5(4)°, ∠ αOCC = 108.6(1)°, ∠ αOCH = 110.4(9)°, and 〈∠ αCCH〉 = 110.5(7)°, where values in parentheses are error estimates (3σ) and those in angle brackets denote average values. The structural differences between the TT and TG conformers were taken from the 4-21G calculations except for the dihedral angles of the TG form, which were determined to be φ 1 = 76(10)° and φ 2 = 161(15)°.

Molecular structure and conformation of diisopropyl sulfide in the vapor phase: reinvestigation by molecular orbital constrained electron diffraction

The conformational properties and molecular structures of diisopropyl sulfide were studied by gas electron diffraction combined with ab initio geometry refinements and calculations of mean amplitudes of vibration. The structures of five stable conformations were obtained by ab initio gradient optimization at the 4-21G/3-321G* level. Conformer I, C 2 symmetry, φ 1 (C 5S 1C 2H 8) = φ 2(C 2S 1C 5H 9)=59(7)°, is identified as the most stable conformer, but the presence and identities of minor concentrations of additional, less stable forms cannot be established with certainty. Comparison of the observed geometry of I with the structures of other organic sulfides shows that the steric repulsion between organic substituents at sulfur is manifested mainly in the SC bond distances, CSC angles and, to a lesser extent, in CC parameters.

Molecular structure of trans-methylchlorovinyl sulphone: A molecular orbital constrained electron diffraction reinvestigation. Evidence for intramolecular hydrogen bonding

Molecular structure of trans-methylchlorovinyl sulphone: A molecular orbital constrained electron diffraction reinvestigation. Evidence for intramolecular hydrogen bonding

The molecular orbital constrained electron diffraction (moced) structural model of quadricyclane determined by electron diffraction combined with ab initio calculations of potential and geometrical parameters

The gas electron diffraction (GED) data of quadicyclane (previously recorded by the University of Tokyo group) were reinvestigated using constraints taken from ab inito (4–21G) gradient geometry and force field calculations. It was the purpose of this study to determine the MOCED structural model for this compound that is obtained when the differences between some unrasolved bond distances and angles in the GED data analysis are constrained to the calculated values. In addition, a novel procedure was tested, in which a scale factor for the ab initio calculated vibrational amplitudes was refined from the diffraction data together with the variable structural parameters. This novel procedure greatly reduces parameter correlation in the least-squares analysis and is expected to be useful whenever extraneous constraints of unresolved parameters are needed for fitting molecular models to the diffraction data. Subject to the ab initio constraints, the analysis yields the following model ( r g-distances, r α-angles; numbers in parentheses are six times the standard deviations of the least-squares intensitv refinements): (CH) = 1.109(1) A, (CC) = 1.526(2) A 1 C 1C 2 = 1.525(24) A, C 2C 6 = 1.525(12) A 1 C 2C 3 = 1.543(24) A 1 C 1C 7 = 1.514(42) A 1 and C 1C 7C 4 = 98.7(6)°. With these parameters, the dependent angles are C 1C 2C 3 = 104.3°, C 1C 2- C 4 = 60°, C 2C 1C 6 = 60 °, and C 2C 1C 7 = 110.6°.

The molecular structure of gaseous methyl vinyl ether at room temperature, studied by molecular orbital constrained electron diffraction and microwave spectroscopy

The gas phase molecular structure of methyl vinyl ether at room temperature has been studied by joint analysis of electron diffraction and microwave data. Constraints on geometrical and thermal parameters were derived from the geometry and force field of the s-cis form, obtained by ab-initio calculations (4–21 G basis set) after complete geometry relaxation. A range of models was investigated that fits all available data (infrared, microwave and electron diffraction). The following rg/rα-parameters were obtained: CC: 1.337 Å, C(sp2)O: 1.359 Å, C(sp3)O: 1.427 Å, <CH> : 1.102 Å ∠CCO : 127.3° and ∠COC: 116.8°. Experimental rgre (ab initio) corrections are given for CC, C(sp2)O and Csp3)O.This investigation demonstrates that molecular orbital constrained electron diffraction is sufficiently reliable and in such a manner that it can be applied to more complicated problems.

ChemInform Abstract: MOLECULAR ORBITAL CONSTRAINED ELECTRON DIFFRACTION STUDIES. 4. CONFORMATIONAL L ANALYSIS OF THE METHYL ESTER OF GLYCINE

Chemischer InformationsdienstVolume 13, Issue 26 Physical Organic Chemistry ChemInform Abstract: MOLECULAR ORBITAL CONSTRAINED ELECTRON DIFFRACTION STUDIES. 4. CONFORMATIONAL L ANALYSIS OF THE METHYL ESTER OF GLYCINE V. J. KLIMKOWSKI, V. J. KLIMKOWSKISearch for more papers by this authorJ. D. EWBANK, J. D. EWBANKSearch for more papers by this authorC. VAN ALSENOY, C. VAN ALSENOYSearch for more papers by this authorJ. N. SCARSDALE, J. N. SCARSDALESearch for more papers by this authorL. + SCHAEFER, L. + SCHAEFERSearch for more papers by this author V. J. KLIMKOWSKI, V. J. KLIMKOWSKISearch for more papers by this authorJ. D. EWBANK, J. D. EWBANKSearch for more papers by this authorC. VAN ALSENOY, C. VAN ALSENOYSearch for more papers by this authorJ. N. SCARSDALE, J. N. SCARSDALESearch for more papers by this authorL. + SCHAEFER, L. + SCHAEFERSearch for more papers by this author First published: June 29, 1982 https://doi.org/10.1002/chin.198226061Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue26June 29, 1982 RelatedInformation

Molecular orbital constrained electron diffraction studies. 4. Conformational analysis of the methyl ester of glycine

Molecular orbital constrained electron diffraction studies. 4. Conformational analysis of the methyl ester of glycine

Structure determination of 1-butene by gas electron diffraction, microwave spectroscopy, molecular mechanics, and molecular orbital constrained electron diffraction

Structure determination of 1-butene by gas electron diffraction, microwave spectroscopy, molecular mechanics, and molecular orbital constrained electron diffraction

ChemInform Abstract: MOLECULAR ORBITAL CONSTRAINED ELECTRON DIFFRACTION STUDIES. CONFORMATIONAL BEHAVIOR OF 1,2‐DIMETHYLHYDRAZINE

Chemischer InformationsdienstVolume 11, Issue 3 Physical Organic Chemistry ChemInform Abstract: MOLECULAR ORBITAL CONSTRAINED ELECTRON DIFFRACTION STUDIES. CONFORMATIONAL BEHAVIOR OF 1,2-DIMETHYLHYDRAZINE N. S. CHIU, N. S. CHIUSearch for more papers by this authorH. L. SELLERS, H. L. SELLERSSearch for more papers by this authorL. + SCHAEFER, L. + SCHAEFERSearch for more papers by this authorK. KOHATA, K. KOHATASearch for more papers by this author N. S. CHIU, N. S. CHIUSearch for more papers by this authorH. L. SELLERS, H. L. SELLERSSearch for more papers by this authorL. + SCHAEFER, L. + SCHAEFERSearch for more papers by this authorK. KOHATA, K. KOHATASearch for more papers by this author First published: January 22, 1980 https://doi.org/10.1002/chin.198003071Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue3January 22, 1980 RelatedInformation

Molecular orbital constrained electron diffraction studies. Conformational behavior of 1,2-dimethylhydrazine

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular orbital constrained electron diffraction studies. Conformational behavior of 1,2-dimethylhydrazineN. S. Chiu, H. L. Sellers, Lothar Schaefer, and K. KohataCite this: J. Am. Chem. Soc. 1979, 101, 20, 5883–5889Publication Date (Print):September 1, 1979Publication History Published online1 May 2002Published inissue 1 September 1979https://doi.org/10.1021/ja00514a003RIGHTS & PERMISSIONSArticle Views46Altmetric-Citations67LEARN 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 (878 KB) Get e-Alerts Get e-Alerts

Molecular orbital constrained gas electron diffraction studies: Part I. Internal rotation in 3-chlorobenzaldehyde

The geometries of the trans and cis forms of 3-chlorobenzaldehyde (I and II, respectively) were optimized using standard single determinant MO theory with the STO—3G basis. The calculated energy difference between I and II was 90 cal mole −1. Mean amplitudes of vibration were calculated for the system by vibrational analysis. Computed molecular properties — amplitude differences and ab initio differences between some geometrical parameters — were combined with the gas electron diffraction data for the compound to constrain least-squares data analysis. The model which was in best agreement with experiment represented a conformational equilibrium with a composition of 64(16)% trans and 36% cis for the vapor of 3-chlorobenzaldehyde at 120°C. This result contradicts a previous vapor phase far infrared investigation of the compound and the torsional potential derived from it. Potentially misleading factors may, therefore, generally have to be taken into account whenever torsional potentials are derived from vibrational data. Beyond the scope of the structural problem considered, the paper demonstrates the advantages of molecular orbital constrained electron diffraction (MOCED) studies.