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Demkiw KM, Hu CT, Woerpel KA. Hyperconjugative Interactions of the Carbon-Halogen Bond that Influence the Geometry of Cyclic α-Haloacetals. J Org Chem 2022; 87:5315-5327. [PMID: 35363473 PMCID: PMC9036965 DOI: 10.1021/acs.joc.2c00148] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The analysis of the structures of low-energy conformers of different α-haloacetals reveals changes in bond lengths and geometries that correspond to stabilizing orbital interactions that contribute to the ground-state structures of these systems. Several factors, including the electron-donating and electron-accepting abilities of the substituents on the ring, affect the degree of the electronic interactions in these carbohydrate-like systems. The presence of an α-halogen atom that can participate in hyperconjugation has been shown to contribute to the structural characteristics of the low-energy conformer. The experimental evidence is supported by natural bond order (NBO) analysis to identify the types of interactions and to assess their relative importance.
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Affiliation(s)
- Krystyna M Demkiw
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States
| | - Chunhua T Hu
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States
| | - K A Woerpel
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States
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2
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Bartolo ND, Demkiw KM, Valentín EM, Hu CT, Arabi AA, Woerpel KA. Diastereoselective Additions of Allylmagnesium Reagents to α-Substituted Ketones When Stereochemical Models Cannot Be Used. J Org Chem 2021; 86:7203-7217. [PMID: 33978419 DOI: 10.1021/acs.joc.1c00553] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The stereoselectivities of reactions of allylmagnesium reagents with chiral ketones cannot be easily explained by stereochemical models. Competition experiments indicate that the complexation step is not reversible, so nucleophiles cannot access the widest range of possible encounter complexes and therefore cannot be analyzed easily using available models. Nevertheless, additions of allylmagnesium reagents to a ketone can still be stereoselective provided that the carbonyl group adopts a conformation that leads to one face being completely blocked from the approach of the allylmagnesium reagent.
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Affiliation(s)
- Nicole D Bartolo
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, United States
| | - Krystyna M Demkiw
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, United States
| | - Elizabeth M Valentín
- St. Mary's College of California, 1928 St. Marys Road, Moraga, California 94575, United States
| | - Chunhua T Hu
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, United States
| | - Alya A Arabi
- Biochemistry Department, College of Medicine and Health Sciences, United Arab Emirates University, P.O. Box 17666, Al Ain, United Arab Emirates.,Centre for Computational Science, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - K A Woerpel
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, United States
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de Melo UZ, Silva RGM, Yamazaki DAS, Pontes RM, Gauze GF, Rosa FA, Rittner R, Basso EA. NMR spectroscopy and theoretical calculations in the conformational analysis of 1-methylpyrrolidin-2-one 3-halo-derivatives. J Phys Chem A 2015; 119:2111-21. [PMID: 25679501 DOI: 10.1021/jp512378g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This study reports the results of ab initio and density functional theory (DFT) electronic structure calculations as well as (3)J(HH) experimental and calculated coupling constant data obtained in the investigation of the conformational equilibrium of 3-halo-derivatives of 1-methylpyrrolidin-2-one. The five-membered ring assumes an envelope conformation owing to the plane of formation of the O═C-N-R bond, with C4 forming the "envelope lid". When the conformation changes, the "lid" alternates between positions above and below the amide plane. The α-carbonyl halogen assumes two positions: a pseudo-axial and a pseudo-equatorial. In the gaseous phase, the calculations indicate that the pseudo-axial conformer is more stable and preferable going down the halogen family. Natural bond orbital analysis showed that electronic delocalization is significant only for the iodo derivative. In the other derivatives, the electrostatic repulsion between oxygen and the halogen determines the conformational equilibrium. When the solvated molecule was taken into account, the pseudo-equatorial conformer population increased with the relative permittivity of the solvent. This variation was strong in the fluoro derivative, and the preference was inverted. In the chlorine derivative, the two populations became closer in methanol and acetonitrile. In the bromine and iodine derivatives, the percentage of pseudo-equatorial conformer increased only slightly owing to the dipole moment of the conformation: the pseudo-equatorial conformation has a greater dipole moment and thus is stable in media with high relative permittivity.
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Affiliation(s)
- Ulisses Zonta de Melo
- Chemistry Department, State University of Maringa , Avenida Colombo, 5790, 87020-900, Maringa, Paraná, Brazil
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4
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Rozada TC, Gauze GF, Rosa FA, Favaro DC, Rittner R, Pontes RM, Basso EA. The conformational analysis of 2-halocyclooctanones. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2015; 137:176-184. [PMID: 25218227 DOI: 10.1016/j.saa.2014.08.052] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 08/05/2014] [Accepted: 08/23/2014] [Indexed: 06/03/2023]
Abstract
The establishment of the most stable structures of eight membered rings is a challenging task to the field of conformational analysis. In this work, a series of 2-halocyclooctanones were synthesized (including fluorine, chlorine, bromine and iodine derivatives) and submitted to conformational studies using a combination of theoretical calculation and infrared spectroscopy. For each compound, four conformations were identified as the most important ones. These conformations are derived from the chair-boat conformation of cyclooctanone. The pseudo-equatorial (with respect to the halogen) conformer is preferred in vacuum and in low polarity solvents for chlorine, bromine and iodine derivatives. For 2-fluorocyclooctanone, the preferred conformation in vacuum is pseudo-axial. In acetonitrile, the pseudo-axial conformer becomes the most stable for the chlorine derivative. According to NBO calculations, the conformational preference is not dictated by electron delocalization, but by classical electrostatic repulsions.
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Affiliation(s)
- Thiago C Rozada
- Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil
| | - Gisele F Gauze
- Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil
| | - Fernanda A Rosa
- Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil
| | - Denize C Favaro
- Instituto de Quimica, Universidade Estadual de Campinas, 13083-970 Campinas, SP, Brazil
| | - Roberto Rittner
- Instituto de Quimica, Universidade Estadual de Campinas, 13083-970 Campinas, SP, Brazil
| | - Rodrigo M Pontes
- Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil
| | - Ernani A Basso
- Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil.
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5
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Braga CB, Ducati LC, Tormena CF, Rittner R. Conformational analysis and intramolecular interactions of L-proline methyl ester and its N-acetylated derivative through spectroscopic and theoretical studies. J Phys Chem A 2014; 118:1748-58. [PMID: 24533966 DOI: 10.1021/jp5007632] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This work reports a detailed study regarding the conformational preferences of L-proline methyl ester (ProOMe) and its N-acetylated derivative (AcProOMe) to elucidate the effects that rule their behaviors, through nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies combined with theoretical calculations. These compounds do not present a zwitterionic form in solution, simulating properly amino acid residues in biological media, in a way closer than amino acids in the gas phase. Experimental (3)JHH coupling constants and infrared data showed excellent agreement with theoretical calculations, indicating no variations in conformer populations on changing solvents. Natural bond orbital (NBO) results showed that hyperconjugative interactions are responsible for the higher stability of the most populated conformer of ProOMe, whereas for AcProOMe both hyperconjugative and steric effects rule its conformational equilibrium.
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Affiliation(s)
- Carolyne B Braga
- Physical Organic Chemistry Laboratory, Chemistry Institute, University of Campinas , 13083-970 Campinas, SP, Brazil
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6
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Melo U, Gauze G, Bagatin M, Pontes R, Basso E. A theoretical and experimental study of the conformational behavior of trans-2-azidocyclohexanol in solution. J Mol Struct 2012. [DOI: 10.1016/j.molstruc.2012.05.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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