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Al-Basheer W. Solvent effects on the vibrational modes of (R)-3-methylcyclohexanone conformers. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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2
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Johnson JL, Polavarapu PL. Chiral Molecular Structure Determination for a Desired Compound Just from Its Molecular Formula and Vibrational Optical Activity Spectra. J Phys Chem A 2021; 125:8000-8013. [PMID: 34478311 DOI: 10.1021/acs.jpca.1c06369] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A novel proof-of-concept model for chiral molecular structure determination using just the molecular formula and vibrational optical activity (VOA) spectra is presented. To verify this concept, the molecular formula of a desired compound is used to generate all possible chiral structural isomers and their VOA spectra are predicted. The similarity analyses of predicted VOA spectra were then carried out in two different ways: (a) similarity between VOA spectrum of one structural isomer with those of the rest, referred to as cross-correlations; (b) similarity between VOA spectra of all chiral structural isomers with the experimental VOA spectra of the desired compound. Three different molecular formulae, C4H8O, C3H5ClO, and C6H10O, and their chiral structural isomers (6, 9, and 75 respectively), were investigated. In each case, the correct chiral molecular structure of the desired compound was identified without ambiguity. Cross-correlation analysis revealed the uniqueness of VOA spectra in deducing the chiral molecular structure solely from its molecular formula. Different chiral structural isomers associated with the molecular formula CH3NO2 were also found to have no significant cross-correlations between their VOA spectra, opening a pathway to detect and identify the elusive chiral N-hydroxyoxaziridine from its VOA spectra.
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Affiliation(s)
- Jordan L Johnson
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Prasad L Polavarapu
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
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3
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Meninno S, Rizzo P, Abbate S, Longhi G, Mazzeo G, Monaco G, Lattanzi A, Zanasi R. Absolute Configuration Assignment of a Paraconic Acid Derivative via Vibrational Circular Dichroism Spectroscopy and Density Functional Theory Calculation. Chirality 2015; 28:110-5. [DOI: 10.1002/chir.22553] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 10/27/2015] [Accepted: 10/28/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Sara Meninno
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università degli Studi Salerno; Fisciano (SA) Italy
| | - Paola Rizzo
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università degli Studi Salerno; Fisciano (SA) Italy
| | - Sergio Abbate
- Dipartimento di Medicina Molecolare e Traslazionale; Università degli Studi di Brescia; Brescia Italy
| | - Giovanna Longhi
- Dipartimento di Medicina Molecolare e Traslazionale; Università degli Studi di Brescia; Brescia Italy
| | - Giuseppe Mazzeo
- Dipartimento di Medicina Molecolare e Traslazionale; Università degli Studi di Brescia; Brescia Italy
| | - Guglielmo Monaco
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università degli Studi Salerno; Fisciano (SA) Italy
| | - Alessandra Lattanzi
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università degli Studi Salerno; Fisciano (SA) Italy
| | - Riccardo Zanasi
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università degli Studi Salerno; Fisciano (SA) Italy
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4
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Al-Basheer W. Matrix-isolation IR spectroscopy ofR-(+)-3-methylcyclopentanone in para-hydrogen crystal. J PHYS ORG CHEM 2015. [DOI: 10.1002/poc.3482] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Watheq Al-Basheer
- Department of Physics; King Fahd University of Petroleum and Minerals; Dhahran 31261 Saudi Arabia
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5
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Kröner D, Gaebel T. Circular Dichroism in Mass Spectrometry: Quantum Chemical Investigations for the Differences between (R)-3-Methylcyclopentanone and Its Cation. J Phys Chem A 2015. [PMID: 26214257 DOI: 10.1021/acs.jpca.5b05247] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In mass spectrometry enantiomers can be distinguished by multiphoton ionization employing circular polarized laser pulses. The circular dichroism (CD) is detected from the normalized difference in the ion yield after excitation with light of opposite handedness. While there are cases in which fragment and parent ions exhibit the same sign of the CD in the ion yield, several experiments show that they might also differ in sign and magnitude. Supported by experimental observations it has been proposed that the parent ion, once it has been formed, is further excited by the laser, which may result in a change of the CD in the ion yield of the formed fragments compared to the parent ion. To gain a deeper insight in possible excitation pathways we calculated and compared the electronic CD absorption spectra of neutral and cationic (R)-3-methylcyclopentanone, applying density functional theory. In addition, electron wavepacket dynamics were used to compare the CD of one- and two-photon transitions. Our results support the proposed subsequent excitation of the parent ion as a possible origin of the difference of the CD in the ion yield between parent ion and fragments.
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6
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Lahiri P, Wiberg KB, Vaccaro PH. Intrinsic Optical Activity and Large-Amplitude Displacement: Conformational Flexibility in (R)-Glycidyl Methyl Ether. J Phys Chem A 2015; 119:8311-27. [DOI: 10.1021/acs.jpca.5b05177] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Priyanka Lahiri
- Department of Chemistry, Yale University, P.O.
Box 208107, New Haven, Connecticut 06520-8107, United States
| | - Kenneth B. Wiberg
- Department of Chemistry, Yale University, P.O.
Box 208107, New Haven, Connecticut 06520-8107, United States
| | - Patrick H. Vaccaro
- Department of Chemistry, Yale University, P.O.
Box 208107, New Haven, Connecticut 06520-8107, United States
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7
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Titze K, Zollitsch T, Heiz U, Boesl U. Laser mass spectrometry with circularly polarized light: circular dichroism of cold molecules in a supersonic gas beam. Chemphyschem 2014; 15:2762-7. [PMID: 25044352 DOI: 10.1002/cphc.201402270] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Indexed: 11/12/2022]
Abstract
An experiment on chiral molecules that combines circular dichroism (CD) spectroscopy, mass-selective detection by laser mass spectrometry (MS), and cooling of molecules by using a supersonic beam is presented. The combination of the former two techniques (CD-laser-MS) is a new method to investigate chiral molecules and is now used by several research groups. Cooling in a supersonic beam supplies a substantial increase in spectroscopic resolution, a feature that has not yet been used in CD spectroscopy. In the experiments reported herein, a large variation in the electronic CD of carbonyl 3-methylcyclopentanone was observed depending on the excited vibrational modes in the n → π* transition. This finding should be of interest for the detection of chiral molecules and for the theoretical understanding of the CD of vibronic bands. It is expected that this effect will show up in other chiral carbonyls because the n → π* transition is typical for the carbonyl group.
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Affiliation(s)
- Katharina Titze
- Chemistry Department, Physical Chemistry Chair, Technische Universität München, Lichtenbergstr. 4, 85748 Garching (Germany), Fax: (+49) 89 289 13389
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Polavarapu PL, Covington CL. Comparison of experimental and calculated chiroptical spectra for chiral molecular structure determination. Chirality 2014; 26:539-52. [PMID: 24644231 DOI: 10.1002/chir.22316] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/26/2014] [Accepted: 02/07/2014] [Indexed: 01/30/2023]
Abstract
For three different chiroptical spectroscopic methods, namely, vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and Raman optical activity (ROA), the measures of similarity of the experimental spectra to the corresponding spectra predicted using quantum chemical theories are summarized. In determining the absolute configuration and/or predominant conformations of chiral molecules, these similarity measures provide numerical estimates of agreement between experimental observations and theoretical predictions. Selected applications illustrating the similarity measures for absorption, circular dichroism, and corresponding dissymmetry factor (DF) spectra, in the case of VCD and ECD, and for Raman, ROA, and circular intensity differential (CID) spectra in the case of ROA, are presented. The analysis of similarity in DF or CID spectra is considered to be much more discerning and accurate than that in absorption (or Raman) and circular dichroism (or ROA) spectra, undertaken individually.
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Scafato P, Caprioli F, Pisani L, Padula D, Santoro F, Mazzeo G, Abbate S, Lebon F, Longhi G. Combined use of three forms of chiroptical spectroscopies in the study of the absolute configuration and conformational properties of 3-phenylcyclopentanone, 3-phenylcyclohexanone, and 3-phenylcycloheptanone. Tetrahedron 2013. [DOI: 10.1016/j.tet.2013.10.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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Lahiri P, Wiberg KB, Vaccaro PH. Intrinsic Optical Activity and Conformational Flexibility: The Role of Size-Dependent Ring Morphology in Model Cycloketones. J Phys Chem A 2013; 117:12382-400. [DOI: 10.1021/jp4089194] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Priyanka Lahiri
- Department of Chemistry, Yale University P.O.
Box 208107, New Haven, Connecticut 06520-8107, United States
| | - Kenneth B. Wiberg
- Department of Chemistry, Yale University P.O.
Box 208107, New Haven, Connecticut 06520-8107, United States
| | - Patrick H. Vaccaro
- Department of Chemistry, Yale University P.O.
Box 208107, New Haven, Connecticut 06520-8107, United States
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11
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Covington CL, Polavarapu PL. Similarity in Dissymmetry Factor Spectra: A Quantitative Measure of Comparison between Experimental and Predicted Vibrational Circular Dichroism. J Phys Chem A 2013; 117:3377-86. [DOI: 10.1021/jp401079s] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Cody L. Covington
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235,
United States
| | - Prasad L. Polavarapu
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235,
United States
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12
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Turchini S, Catone D, Zema N, Contini G, Prosperi T, Decleva P, Stener M, Rondino F, Piccirillo S, Prince KC, Speranza M. Conformational Sensitivity in Photoelectron Circular Dichroism of 3-Methylcyclopentanone. Chemphyschem 2013; 14:1723-32. [DOI: 10.1002/cphc.201200975] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 02/13/2013] [Indexed: 11/08/2022]
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13
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Al-Basheer W. Solvent Effects on IR Modes of (R)-3-Methylcyclopentanone Conformers: A Computational Investigation. J SOLUTION CHEM 2012. [DOI: 10.1007/s10953-012-9890-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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14
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Lahiri P, Wiberg KB, Vaccaro PH. A Tale of Two Carenes: Intrinsic Optical Activity and Large-Amplitude Nuclear Displacement. J Phys Chem A 2012; 116:9516-33. [DOI: 10.1021/jp303270d] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Priyanka Lahiri
- Department
of Chemistry, Yale University, P.O. Box
208107, New Haven, Connecticut 06520-8107, United States
| | - Kenneth B. Wiberg
- Department
of Chemistry, Yale University, P.O. Box
208107, New Haven, Connecticut 06520-8107, United States
| | - Patrick H. Vaccaro
- Department
of Chemistry, Yale University, P.O. Box
208107, New Haven, Connecticut 06520-8107, United States
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15
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Logé C, Boesl U. Laser mass spectrometry with circularly polarized light: two-photon circular dichroism. Phys Chem Chem Phys 2012; 14:11981-9. [DOI: 10.1039/c2cp41405h] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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16
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Kröner D. Chiral distinction by ultrashort laser pulses: electron wavepacket dynamics incorporating magnetic interactions. J Phys Chem A 2011; 115:14510-8. [PMID: 22010997 DOI: 10.1021/jp207270s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The qualitative and quantitative distinction of enantiomers is one of the key issues in chemical analysis. In the last years, circular dichroism (CD) has been combined with laser ionization mass spectrometry (LIMS), applying resonance enhanced multiphoton ionization (REMPI) with ultrashort laser pulses. We present theoretical investigations on the CD in the populations of the first electronic excited state of the REMPI process, caused by the interaction of 3-methyl-cyclopentanone with either left or right circular polarized fs-laser pulses. For this we performed multistate laser driven many electron dynamics based on ab initio electronic structure calculations, namely, TD-CIS(D)/6-311++(2d,2p). For a theoretical description of these experiments, a complete description of the field-dipole correlation is mandatory, including both electric field-electric dipole and magnetic field-magnetic dipole interactions. The effect of various pulse parameters on the CD are analyzed and compared with experimental results to gain further understanding of the key elements for an optimal distinction of enantiomers.
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Affiliation(s)
- Dominik Kröner
- Chemistry Department-Theoretical Chemistry, Universität Potsdam, Potsdam, Germany.
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17
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Pescitelli G, Di Bari L, Berova N. Conformational aspects in the studies of organic compounds by electronic circular dichroism. Chem Soc Rev 2011; 40:4603-25. [PMID: 21677932 DOI: 10.1039/c1cs15036g] [Citation(s) in RCA: 278] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The electronic circular dichroism (ECD) spectra of flexible molecules include the contributions of all conformers populated at the working temperature. ECD spectra of chiral substrates depend on their stereochemistry in terms of both absolute configuration, as reflected in the sign of the spectrum, and molecular conformation, which dictates the overall spectral shape (possibly including the sign) in a very sensitive manner. The unique high sensitivity of ECD towards conformation, as well as of other chiroptical spectroscopies, renders these techniques a useful alternative or complement to standard spectroscopic tools for conformational investigations, such as NMR. This tutorial review provides first a brief discussion of the main principles of ECD spectroscopy and related methods for interpretation of spectra, with special reference to conformational aspects. The review focuses on the common problems encountered in the application of ECD for assignments of absolute configuration of flexible molecules. These problems can be handled either by taking into account the whole conformational ensemble or by considering rigid derivatives prepared ad hoc. Finally, the review presents the relatively less common but very interesting application of ECD spectroscopy for conformational analyses of organic compounds.
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Affiliation(s)
- Gennaro Pescitelli
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, I-56126 Pisa, Italy
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18
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Horsch P, Urbasch G, Weitzel KM, Kröner D. Circular dichroism in ion yields employing femtosecond laser ionization—the role of laser pulse duration. Phys Chem Chem Phys 2011; 13:2378-86. [DOI: 10.1039/c0cp01903h] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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19
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Yang G, Xu Y, Hou J, Zhang H, Zhao Y. Determination of the Absolute Configuration of Pentacoordinate Chiral Phosphorus Compounds in Solution by Using Vibrational Circular Dichroism Spectroscopy and Density Functional Theory. Chemistry 2010; 16:2518-27. [DOI: 10.1002/chem.200902501] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Breunig HG, Urbasch G, Horsch P, Cordes J, Koert U, Weitzel KM. Circular Dichroism in Ion Yields of Femtosecond-Laser Mass Spectrometry. Chemphyschem 2009; 10:1199-202. [DOI: 10.1002/cphc.200900103] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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21
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Lin N, Santoro F, Zhao X, Rizzo A, Barone V. Vibronically Resolved Electronic Circular Dichroism Spectra of (R)-(+)-3-Methylcyclopentanone: A Theoretical Study. J Phys Chem A 2008; 112:12401-11. [DOI: 10.1021/jp8064695] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Na Lin
- Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden, Institute of Crystal Materials, Shandong University, 250100 Jinan, Shandong, People’s Republic of China, and Area della Ricerca, Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G. Moruzzi 1, I-56124 Pisa, Italy
| | - Fabrizio Santoro
- Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden, Institute of Crystal Materials, Shandong University, 250100 Jinan, Shandong, People’s Republic of China, and Area della Ricerca, Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G. Moruzzi 1, I-56124 Pisa, Italy
| | - Xian Zhao
- Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden, Institute of Crystal Materials, Shandong University, 250100 Jinan, Shandong, People’s Republic of China, and Area della Ricerca, Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G. Moruzzi 1, I-56124 Pisa, Italy
| | - Antonio Rizzo
- Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden, Institute of Crystal Materials, Shandong University, 250100 Jinan, Shandong, People’s Republic of China, and Area della Ricerca, Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G. Moruzzi 1, I-56124 Pisa, Italy
| | - Vincenzo Barone
- Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden, Institute of Crystal Materials, Shandong University, 250100 Jinan, Shandong, People’s Republic of China, and Area della Ricerca, Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G. Moruzzi 1, I-56124 Pisa, Italy
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22
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Lin N, Luo Y, Santoro F, Zhao X, Rizzo A. Vibronically-induced change in the chiral response of molecules revealed by electronic circular dichroism spectroscopy. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.09.013] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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23
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Rizzo A, Lin N, Ruud K. Ab initio study of the one- and two-photon circular dichroism of R-(+)-3-methyl-cyclopentanone. J Chem Phys 2008; 128:164312. [PMID: 18447444 DOI: 10.1063/1.2907727] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Affiliation(s)
- Antonio Rizzo
- Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR), Area della Ricerca, Via G. Moruzzi 1, I-56124 Pisa, Italy
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Al-Basheer W, Pagni RM, Compton RN. Spectroscopic and theoretical investigation of (R)-3-methylcyclopentanone. The effect of solvent and temperature on the distribution of conformers. J Phys Chem A 2007; 111:2293-8. [PMID: 17388310 DOI: 10.1021/jp068320d] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Temperature-dependent electronic circular dichroism (CD) spectra are reported for (R)-(+)-3-methylcyclopentanone (R3MCP) in 34 solvents. Analysis of these data yielded the enthalpy and entropy differences between axial methyl and equatorial methyl conformers, the dominant conformers for R3MCP. The weakly absorbing n-->pi* transition exhibited a decrease in lambdamax as the solvent polarity increased. Vibrational CD fine structure of the n-->pi* transition was observed in the gas phase in addition to several of the solvents. Vapor-phase CD spectra were compared to both the solution-phase spectra and theoretical calculations of the axial and equatorial methyl conformers. Optical rotation (OR) measurements for R3MCP in cyclohexane solution in the visible region showed excellent agreement with OR DFT calculations of the equatorial and axial methyl conformers. Density functional calculations with B3LYP and the 6-13G* and aug-cc-pVDZ basis sets, which incorporate the solvent dielectric constant, yielded trends in thermodynamic quantities as a function of polarity and solvent dipole moments that are only weakly or not observed in experiments.
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Affiliation(s)
- Watheq Al-Basheer
- Department of Physics, University of Tennessee, Knoxville, Tennessee 37996, USA
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25
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Li R, Sullivan R, Al-Basheer W, Pagni RM, Compton RN. Linear and nonlinear circular dichroism of R-(+)-3-methylcyclopentanone. J Chem Phys 2006; 125:144304. [PMID: 17042587 DOI: 10.1063/1.2338519] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Linear and nonlinear circular dichroism of R-(+)-3-methylcyclopentanone (R-3MCP) is reported in the gas and liquid phases. Measurements of (2+1) resonance-enhanced multiphoton ionization circular dichroism (REMPICD) for nozzle-jet expanded molecular beams of the equatorial conformer of R-3MCP are presented. Monitoring either mass-selected cations or photoelectrons produced via (2+1) REMPI through the n --> 3s Rydberg transition yielded a REMPICD of +1.5+/-0.5% [REMPICD identical with 2(I(L)-I(R))(I(L)+I(R))], where I(L/R) refers to the ion/electron signal for left/right circularly polarized light. A racemic mixture of 3-methylcyclopentanone showed no significant CD; however, the signal fluctuations were much larger than that observed for the resolved R-(+)-3-methylcyclopentanone as might be expected for the small number of ions produced from slightly unequal numbers of enantiomers in each laser shot. Gas phase, vibrationally resolved, one-photon CD for vapor phase R-(+)-3-methylcyclopentanone (i.e., admixture of five axial and equatorial forms) was measured to be approximately 0 and -0.004 at photon energies corresponding to the one- (nonresonant) and two-(3s resonance) photon energy levels. The one-photon CD (of the room temperature population of conformers) at an energy corresponding to the ionization step was measured previously to be approximately +0.0011 which is of the same sign as the REMPICD. The first step is also near a positive CD region. This suggests that the (2+1) REMPICD is determined primarily by both the initial and continuum steps. The one-photon CDs for the equatorial and axial forms of 3MCP are calculated, using GAUSSIAN03, to be approximately equal but having opposite sign for the transitions of interest. The CD for 3MCP in cyclohexane is found to be strongly temperature dependent as a result of the presence of both the axial and equatorial conformers. The energy difference between the two conformers is determined from a van't Hoff plot of these data to be 3.50+/-0.05 kJ/mole in cyclohexane and is approximately 1 kJ/mole smaller than measurements employing other methods.
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Affiliation(s)
- R Li
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
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26
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Fristrup P, Lassen PR, Johannessen C, Tanner D, Norrby PO, Jalkanen KJ, Hemmingsen L. Direct Determination of Absolute Configuration of Methyl-Substituted Phenyloxiranes: Combined Experimental and Theoretical Approach. J Phys Chem A 2006; 110:9123-9. [PMID: 16854024 DOI: 10.1021/jp060154m] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++G*, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and related to the physical structure of the compounds. The absolute configuration could be established directly in each case by comparing experimental and theoretical spectra. In addition, we have been able to document the changes that occur both in structures and in the VA and VCD spectra due to substituent effects on the oxirane ring.
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Affiliation(s)
- Peter Fristrup
- Center for Sustainable and Green Chemistry, Department of Chemistry, Technical University of Denmark, Building 201 Kemitorvet, DK-2800 Kgs. Lyngby, Denmark.
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Schühly W, Crockett SL, Fabian WMF. Hyperolactone C: Determination of its absolute configuration by comparison of experimental and calculated CD spectra. Chirality 2005; 17:250-6. [PMID: 15841475 DOI: 10.1002/chir.20164] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
A detailed conformational analysis of hyperolactone C diastereomers and enantiomers ((5R,9R),(5S,9S) and (5S,9R),(5R,9S)) was done with molecular mechanics and density functional theory methods. Time-dependent density functional theory (B3PW91/TZVP) was used to calculate electronic transition energies (UV/vis spectra) and rotational strengths of the respective conformations. The effect of solvation (acetonitrile solution) on excitation energies and electronic circular dichroism was approximated by the polarizable continuum model. By comparison of the simulated CD spectrum with that measured for hyperolactone C isolated from Hypericum lloydii, its absolute configuration can be assigned as (5S,9S).
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Affiliation(s)
- Wolfgang Schühly
- Institut für Pharmazeutische Wissenschaften--Pharmakognosie, Karl-Franzens Universität Graz, Austria
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