1
|
Changala PB, Franke PR, Stanton JF, Ellison GB, McCarthy MC. Direct Probes of π-Delocalization in Prototypical Resonance-Stabilized Radicals: Hyperfine-Resolved Microwave Spectroscopy of Isotopic Propargyl and Cyanomethyl. J Am Chem Soc 2024; 146:1512-1521. [PMID: 38170910 DOI: 10.1021/jacs.3c11220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Delocalization of the unpaired electron in π-conjugated radicals has profound implications for their chemistry, but direct and quantitative characterization of this electronic structure in isolated molecules remains challenging. We apply hyperfine-resolved microwave rotational spectroscopy to rigorously probe π-delocalization in propargyl, CH2CCH, a prototypical resonance-stabilized radical and key reactive intermediate. Using the spectroscopic constants derived from the high-resolution cavity Fourier transform microwave measurements of an exhaustive set of 13C- and 2H-substituted isotopologues, together with high-level ab initio calculations of zero-point vibrational effects, we derive its precise semiexperimental equilibrium geometry and quantitatively characterize the spatial distribution of its unpaired electron. Our results highlight the importance of considering both spin-polarization and orbital-following contributions when interpreting the isotropic hyperfine coupling constants of π radicals. These physical insights are strengthened by a parallel analysis of the isoelectronic species cyanomethyl, CH2CN, using new 13C measurements also reported in this work. A detailed comparison of the structure and electronic properties of propargyl, cyanomethyl, and other closely related species allows us to correlate trends in their chemical bonding and electronic structure with critical changes in their reactivity and thermochemistry.
Collapse
Affiliation(s)
- P Bryan Changala
- Center for Astrophysics|Harvard & Smithsonian, Cambridge, Massachusetts 02138, United States
| | - Peter R Franke
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - John F Stanton
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - G Barney Ellison
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Michael C McCarthy
- Center for Astrophysics|Harvard & Smithsonian, Cambridge, Massachusetts 02138, United States
| |
Collapse
|
2
|
Esselman BJ, Zdanovskaia MA, Owen AN, Stanton JF, Woods RC, McMahon RJ. Precise Equilibrium Structure of Benzene. J Am Chem Soc 2023; 145:21785-21797. [PMID: 37774420 DOI: 10.1021/jacs.3c03109] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/01/2023]
Abstract
Recent advances in gas-phase structure determination afford outstanding agreement between the CCSD(T)/cc-pCVTZ-corrected semi-experimental (reSE) equilibrium structures and their corresponding best theoretical estimates (BTEs) of the equilibrium structures (re) based upon corrections to the CCSD(T)/cc-pCV5Z geometries for the aromatic heterocycles pyrimidine and pyridazine. Herein, that same analysis is extended to the fundamental aromatic molecule benzene, using published experimental spectroscopic data for a total of 11 available isotopologues. The incorporation of rotational constants from all of these isotopologues and CCSD(T) corrections to address the impacts of both the vibration-rotation interaction and electron-mass distribution results in a highly precise and accurate reSE structure. The CCSD(T)/cc-pCV5Z optimized geometry has been further corrected to address a finite basis set, untreated electron correlation, relativistic effects, and a breakdown of the Born-Oppenheimer approximation. This analysis achieves outstanding agreement between the re (BTE) and reSE structural parameters of benzene to a highly satisfying level (0.0001 Å), an agreement that surpasses our recently published structures of the aforementioned nitrogen-substituted benzene analogues. The D6h geometry of benzene is now known to an unprecedented precision: RC-C = 1.3913 (1) Å and RC-H = 1.0809 (1) Å. The mutual agreement between theory and experiment presented in this work validates both, substantially resolving all discrepancies between the reSE and theoretical re structures available in the literature.
Collapse
Affiliation(s)
- Brian J Esselman
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706-1322, United States
| | - Maria A Zdanovskaia
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706-1322, United States
| | - Andrew N Owen
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706-1322, United States
| | - John F Stanton
- Quantum Theory Project, Departments of Physics and Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - R Claude Woods
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706-1322, United States
| | - Robert J McMahon
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706-1322, United States
| |
Collapse
|
3
|
Changala PB, Genossar-Dan N, Brudner E, Gur T, Baraban JH, McCarthy MC. Structural and electronic trends of optical cycling centers in polyatomic molecules revealed by microwave spectroscopy of MgCCH, CaCCH, and SrCCH. Proc Natl Acad Sci U S A 2023; 120:e2303586120. [PMID: 37399375 PMCID: PMC10334755 DOI: 10.1073/pnas.2303586120] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 05/23/2023] [Indexed: 07/05/2023] Open
Abstract
The unique optical cycling efficiency of alkaline earth metal-ligand molecules has enabled significant advances in polyatomic laser cooling and trapping. Rotational spectroscopy is an ideal tool for probing the molecular properties that underpin optical cycling, thereby elucidating the design principles for expanding the chemical diversity and scope of these platforms for quantum science. We present a comprehensive study of the structure and electronic properties in alkaline earth metal acetylides with high-resolution microwave spectra of 17 isotopologues of MgCCH, CaCCH, and SrCCH in their 2Σ+ ground electronic states. The precise semiexperimental equilibrium geometry of each species has been derived by correcting the measured rotational constants for electronic and zero-point vibrational contributions calculated with high-level quantum chemistry methods. The well-resolved hyperfine structure associated with the 1,2H, 13C, and metal nuclear spins provides further information on the distribution and hybridization of the metal-centered, optically active unpaired electron. Together, these measurements allow us to correlate trends in chemical bonding and structure with the electronic properties that promote efficient optical cycling essential to next-generation experiments in precision measurement and quantum control of complex polyatomic molecules.
Collapse
Affiliation(s)
- P. Bryan Changala
- Atomic and Molecular Physics Division, Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA02138
| | - Nadav Genossar-Dan
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva8410501, Israel
| | - Ella Brudner
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva8410501, Israel
| | - Tomer Gur
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva8410501, Israel
| | - Joshua H. Baraban
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva8410501, Israel
| | - Michael C. McCarthy
- Atomic and Molecular Physics Division, Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA02138
| |
Collapse
|
4
|
Ceselin G, Barone V, Tasinato N. Accurate Biomolecular Structures by the Nano-LEGO Approach: Pick the Bricks and Build Your Geometry. J Chem Theory Comput 2021; 17:7290-7311. [PMID: 34666488 PMCID: PMC8582257 DOI: 10.1021/acs.jctc.1c00788] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The determination
of accurate equilibrium molecular structures
plays a fundamental role for understanding many physical–chemical
properties of molecules, ranging from the precise evaluation of the
electronic structure to the analysis of the role played by dynamical
and environmental effects in tuning their overall behavior. For small
semi-rigid systems in the gas phase, state-of-the-art quantum chemical
computations rival the most sophisticated experimental (from, for
example, high-resolution spectroscopy) results. For larger molecules,
more effective computational approaches must be devised. To this end,
we have further enlarged the compilation of available semi-experimental
(SE) equilibrium structures, now covering the most important fragments
containing H, B, C, N, O, F, P, S, and Cl atoms collected in the new
SE100 database. Next, comparison with geometries optimized by methods
rooted in the density functional theory showed that the already remarkable
results delivered by PW6B95 and, especially, rev-DSDPBEP86 functionals
can be further improved by a linear regression (LR) approach. Use
of template fragments (taken from the SE100 library) together with
LR estimates for the missing interfragment parameters paves the route
toward accurate structures of large molecules, as witnessed by the
very small deviations between computed and experimental rotational
constants. The whole approach has been implemented in a user-friendly
tool, termed nano-LEGO, and applied to a number of demanding case
studies.
Collapse
Affiliation(s)
- Giorgia Ceselin
- Scuola Normale Superiore, Piazza Dei Cavalieri 7, I-56126 Pisa, Italy
| | - Vincenzo Barone
- Scuola Normale Superiore, Piazza Dei Cavalieri 7, I-56126 Pisa, Italy
| | - Nicola Tasinato
- Scuola Normale Superiore, Piazza Dei Cavalieri 7, I-56126 Pisa, Italy
| |
Collapse
|
5
|
Affiliation(s)
- Jean Demaison
- Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), CP160/09, Faculté des Sciences, Université Libre de Bruxelles (U.L.B.) Brussels, Belgium
| | - Jacques Liévin
- Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), CP160/09, Faculté des Sciences, Université Libre de Bruxelles (U.L.B.) Brussels, Belgium
| |
Collapse
|
6
|
Salta Z, Segovia ME, Katz A, Tasinato N, Barone V, Ventura ON. Isomerization and Fragmentation Reactions on the [C 2SH 4] Potential Energy Surface: The Metastable Thione S-Methylide Isomer. J Org Chem 2021; 86:2941-2956. [PMID: 33501826 PMCID: PMC8023414 DOI: 10.1021/acs.joc.0c02835] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Thione S-methylide, parent species of the thiocarbonyl ylide family, is a 1,3-dipolar species on the [C2SH4] potential energy surface, not so much studied as its isomers, thiirane, vinyl thiol, and thioacetaldehyde. The conrotatory ring-closure reaction toward thiirane was studied in the 90s, but no complete analysis of the potential energy surface is available. In this paper, we report a computational study of the reaction scheme linking all species. We employed several computational methods (density functional theory, CCSD(T) composite schemes, and CASSCF/CASPT2 multireference procedures) to find the best description of thione S-methylide, its isomers, and transition states. The barrier from thiirane to thione S-methylide amounts to 52.2 kcal mol-1 (against 17.6 kcal mol-1 for the direct one), explaining why thiocarbonyl ylides cannot be prepared from thiiranes. Conversion of thiirane to vinyl thiol implies a large barrier, supporting why the reaction has been observed only at high temperatures. Fragmentations of thiirane to S(3P) or S(1D) and ethylene as well as decomposition to hydrogen sulfide plus acetylene were also explored. Triplet and singlet open-shell species were identified as intermediates in the fragmentations, with energies lower than the transition state between thiirane and vinyl thiol, explaining the preference of the latter at low temperatures.
Collapse
Affiliation(s)
- Zoi Salta
- Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
| | - Marc E Segovia
- Computational Chemistry and Biology Group, CCBG, DETEMA, Facultad de Química, Universidad de la República, 11400 Montevideo, Uruguay
| | - Aline Katz
- Computational Chemistry and Biology Group, CCBG, DETEMA, Facultad de Química, Universidad de la República, 11400 Montevideo, Uruguay
| | - Nicola Tasinato
- Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
| | - Vincenzo Barone
- Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
| | - Oscar N Ventura
- Computational Chemistry and Biology Group, CCBG, DETEMA, Facultad de Química, Universidad de la República, 11400 Montevideo, Uruguay
| |
Collapse
|
7
|
Müller HS, Thorwirth S, Lewen F. Rotational spectroscopy of singly 13C substituted isotopomers of propyne and determination of a semi-empirical equilibrium structure. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2020.127769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
8
|
Šmydke J, Fábri C, Sarka J, Császár AG. Rovibrational quantum dynamics of the vinyl radical and its deuterated isotopologues. Phys Chem Chem Phys 2019; 21:3453-3472. [DOI: 10.1039/c8cp04672g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Rotational–vibrational states up to 3200 cm−1, beyond the highest-lying stretching fundamental, are computed variationally for the vinyl radical (VR), H2CβCαH, and the following deuterated isotopologues of VR: CH2CD, CHDCH, and CD2CD.
Collapse
Affiliation(s)
- Jan Šmydke
- MTA-ELTE Complex Chemical Systems Research Group and Laboratory of Molecular Structure and Dynamics
- Institute of Chemistry
- ELTE Eötvös Loránd University
- H-1117 Budapest
- Hungary
| | - Csaba Fábri
- MTA-ELTE Complex Chemical Systems Research Group and Laboratory of Molecular Structure and Dynamics
- Institute of Chemistry
- ELTE Eötvös Loránd University
- H-1117 Budapest
- Hungary
| | - János Sarka
- Department of Chemistry and Biochemistry
- Texas Tech University
- Lubbock
- USA
| | - Attila G. Császár
- MTA-ELTE Complex Chemical Systems Research Group and Laboratory of Molecular Structure and Dynamics
- Institute of Chemistry
- ELTE Eötvös Loránd University
- H-1117 Budapest
- Hungary
| |
Collapse
|
9
|
Doney KD, Zhao D, Stanton JF, Linnartz H. Theoretical investigation of the infrared spectrum of small polyynes. Phys Chem Chem Phys 2018; 20:5501-5508. [DOI: 10.1039/c7cp06131e] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The ro-vibrational parameters of small polyynes are calculated at the CCSD(T)/ANO1 level, including the first anharmonic vibrational frequencies of tetraacetylene.
Collapse
Affiliation(s)
- Kirstin D. Doney
- Sackler Laboratory for Astrophysics
- Leiden Observatory
- Leiden University
- Leiden
- The Netherlands
| | - Dongfeng Zhao
- CAS Center for Excellence in Quantum Information and Quantum Physics and Hefei National Laboratory for Physical Sciences at the Microscale
- University of Science and Technology of China
- Hefei
- P. R. China
| | | | - Harold Linnartz
- Sackler Laboratory for Astrophysics
- Leiden Observatory
- Leiden University
- Leiden
- The Netherlands
| |
Collapse
|
10
|
Feller D. Estimating the intrinsic limit of the Feller-Peterson-Dixon composite approach when applied to adiabatic ionization potentials in atoms and small molecules. J Chem Phys 2017; 147:034103. [DOI: 10.1063/1.4993625] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
11
|
Møllendal H, Samdal S, Guillemin JC. Microwave and Quantum Chemical Study of Intramolecular Hydrogen Bonding in 2-Propynylhydrazine (HC≡CCH2NHNH2). J Phys Chem A 2016; 120:4071-8. [PMID: 27196111 DOI: 10.1021/acs.jpca.6b03796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The microwave spectrum of 2-propynylhydrazine (HC≡CCH2NHNH2) was investigated in the 23-124 GHz spectral interval. The spectra of two conformers denoted I and II were assigned. I is the lower-energy form, and relative intensity measurements yielded an internal energy difference of 3.0(4) kJ/mol between I and II. The spectra of the ground and five vibrationally excited states were assigned for I, whereas only the spectrum of the ground vibrational state was assigned for II. Both I and II are each stabilized simultaneously by two intramolecular hydrogen bonds. The first of these hydrogen bonds is formed between the hydrogen atom of the -NH- part of the hydrazino group, and the second internal hydrogen bond is formed between one of the hydrogen atoms of the -NH2 part. The π-electrons of the triple bond is thus shared by these two hydrogen atoms. The shortest contact between a hydrogen atom of the hydrazino group and the π-electrons of the ethynyl group is found in lower-energy conformer I. The conformational properties of 2-propynylhydrazine were explored by MP2/cc-pVTZ and CCSD/cc-pVQZ calculations. The CCSD method predicts that seven rotameric forms exist for this compound. Five of these rotamers are stabilized by internal hydrogen bonding. The simultaneous sharing of the π-electrons of the triple bond by two hydrogen atoms occurs only in Conformers I and II, which are predicted to be the two forms with the lowest energies, with I 2.52 kJ/mol lower in energy than II. The effective rotational constants of the ground vibrational states of I and II were predicted by a combination of MP2 and CCSD calculations, whereas centrifugal distortion constants and vibration-rotation constants were calculated by the MP2 method. The theoretical spectroscopic constants are compared with the experimental counterparts. It is concluded that more refined calculations are necessary to obtain complete agreement.
Collapse
Affiliation(s)
- Harald Møllendal
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo , P.O. Box 1033, Blindern, NO-0315 Oslo, Norway
| | - Svein Samdal
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo , P.O. Box 1033, Blindern, NO-0315 Oslo, Norway
| | - Jean-Claude Guillemin
- Institut des Sciences Chimiques de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226 , 11 Allée de Beaulieu, CS 50837, 35708 Rennes Cedex 7, France
| |
Collapse
|