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Kovács B, Földes T, Szabó M, Dorkó É, Kótai B, Laczkó G, Holczbauer T, Domján A, Pápai I, Soós T. Illuminating the multiple Lewis acidity of triaryl-boranes via atropisomeric dative adducts. Chem Sci 2024:d4sc00925h. [PMID: 39257854 PMCID: PMC11382148 DOI: 10.1039/d4sc00925h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Accepted: 08/23/2024] [Indexed: 09/12/2024] Open
Abstract
Using the principle that constrained conformational spaces can generate novel and hidden molecular properties, we challenged the commonly held perception that a single-centered Lewis acid reacting with a single-centered Lewis base always forms a single Lewis adduct. Accordingly, the emergence of single-centered but multiple Lewis acidity among sterically hindered and non-symmetric triaryl-boranes is reported. These Lewis acids feature several diastereotopic faces providing multiple binding sites at the same Lewis acid center in the interaction with Lewis bases giving rise to adducts with diastereomeric structures. We demonstrate that with a proper choice of the base, atropisomeric adduct species can be formed that interconvert via the dissociative mechanism rather than conformational isomerism. The existence of this exotic and peculiar molecular phenomenon was experimentally confirmed by the formation of atropisomeric piperidine-borane adducts using state-of-the-art NMR techniques in combination with computational methods.
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Affiliation(s)
- Benjámin Kovács
- Centre for Structural Science, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Tamás Földes
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Márk Szabó
- Centre for Structural Science, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Éva Dorkó
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Bianka Kótai
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Gergely Laczkó
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
- Hevesy György PhD School of Chemistry, Eötvös Loránd University P. O. Box 32 Budapest H-1518 Hungary
| | - Tamás Holczbauer
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Attila Domján
- Centre for Structural Science, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Imre Pápai
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
| | - Tibor Soós
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences Magyar tudósok körútja 2 H-1117 Budapest Hungary
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Sherard MM, Kaplan JS, Simpson JH, Kittredge KW, Leopold MC. Functionalized Gold Nanoparticles and Halogen Bonding Interactions Involving Fentanyl and Fentanyl Derivatives. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:917. [PMID: 38869542 PMCID: PMC11173406 DOI: 10.3390/nano14110917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Revised: 05/14/2024] [Accepted: 05/19/2024] [Indexed: 06/14/2024]
Abstract
Fentanyl (FTN) and synthetic analogs of FTN continue to ravage populations across the globe, including in the United States where opioids are increasingly being used and abused and are causing a staggering and growing number of overdose deaths each year. This growing pandemic is worsened by the ease with which FTN can be derivatized into numerous derivatives. Understanding the chemical properties/behaviors of the FTN class of compounds is critical for developing effective chemical detection schemes using nanoparticles (NPs) to optimize important chemical interactions. Halogen bonding (XB) is an intermolecular interaction between a polarized halogen atom on a molecule and e--rich sites on another molecule, the latter of which is present at two or more sites on most fentanyl-type structures. Density functional theory (DFT) is used to identify these XB acceptor sites on different FTN derivatives. The high toxicity of these compounds necessitated a "fragmentation" strategy where smaller, non-toxic molecules resembling parts of the opioids acted as mimics of XB acceptor sites present on intact FTN and its derivatives. DFT of the fragments' interactions informed solution measurements of XB using 19F NMR titrations as well as electrochemical measurements of XB at self-assembled monolayer (SAM)-modified electrodes featuring XB donor ligands. Gold NPs, known as monolayer-protected clusters (MPCs), were also functionalized with strong XB donor ligands and assembled into films, and their interactions with FTN "fragments" were studied using voltammetry. Ultimately, spectroscopy and TEM analysis were combined to study whole-molecule FTN interactions with the functionalized MPCs in solution. The results suggested that the strongest XB interaction site on FTN, while common to most of the drug's derivatives, is not strong enough to induce NP-aggregation detection but may be better exploited in sensing schemes involving films.
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Affiliation(s)
- Molly M. Sherard
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, VA 23173, USA; (M.M.S.); (J.S.K.); (J.H.S.)
| | - Jamie S. Kaplan
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, VA 23173, USA; (M.M.S.); (J.S.K.); (J.H.S.)
| | - Jeffrey H. Simpson
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, VA 23173, USA; (M.M.S.); (J.S.K.); (J.H.S.)
| | - Kevin W. Kittredge
- Department of Chemistry, Joan P. Brock School of Math and Natural Sciences, Virginia Wesleyan College, Virginia Beach, VA 23455, USA;
| | - Michael C. Leopold
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, VA 23173, USA; (M.M.S.); (J.S.K.); (J.H.S.)
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3
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Amonov A, Scheiner S. Relation between Halogen Bond Strength and IR and NMR Spectroscopic Markers. Molecules 2023; 28:7520. [PMID: 38005241 PMCID: PMC10673387 DOI: 10.3390/molecules28227520] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 11/04/2023] [Accepted: 11/08/2023] [Indexed: 11/26/2023] Open
Abstract
The relationship between the strength of a halogen bond (XB) and various IR and NMR spectroscopic quantities is assessed through DFT calculations. Three different Lewis acids place a Br or I atom on a phenyl ring; each is paired with a collection of N and O bases of varying electron donor power. The weakest of the XBs display a C-X bond contraction coupled with a blue shift in the associated frequency, whereas the reverse trends occur for the stronger bonds. The best correlations with the XB interaction energy are observed with the NMR shielding of the C atom directly bonded to X and the coupling constants involving the C-X bond and the C-H/F bond that lies ortho to the X substituent, but these correlations are not accurate enough for the quantitative assessment of energy. These correlations tend to improve as the Lewis acid becomes more potent, which makes for a wider range of XB strengths.
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Affiliation(s)
- Akhtam Amonov
- Department of Optics and Spectroscopy, Engineering Physics Institute, Samarkand State University, University blv. 15, Samarkand 140104, Uzbekistan;
| | - Steve Scheiner
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA
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4
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Puttreddy R, Rautiainen JM, Yu S, Rissanen K. N-X⋅⋅⋅O-N Halogen Bonds in Complexes of N-Haloimides and Pyridine-N-oxides: A Large Data Set Study. Angew Chem Int Ed Engl 2023; 62:e202307372. [PMID: 37314001 DOI: 10.1002/anie.202307372] [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: 05/25/2023] [Revised: 06/13/2023] [Accepted: 06/14/2023] [Indexed: 06/15/2023]
Abstract
N-X⋅⋅⋅- O-N+ halogen-bonded systems formed by 27 pyridine N-oxides (PyNOs) as halogen-bond (XB) acceptors and two N-halosuccinimides, two N-halophthalimides, and two N-halosaccharins as XB donors are studied in silico, in solution, and in the solid state. This large set of data (132 DFT optimized structures, 75 crystal structures, and 168 1 H NMR titrations) provides a unique view to structural and bonding properties. In the computational part, a simple electrostatic model (SiElMo) for predicting XB energies using only the properties of halogen donors and oxygen acceptors is developed. The SiElMo energies are in perfect accord with energies calculated from XB complexes optimized with two high-level DFT approaches. Data from in silico bond energies and single-crystal X-ray structures correlate; however, data from solution do not. The polydentate bonding characteristic of the PyNOs' oxygen atom in solution, as revealed by solid-state structures, is attributed to the lack of correlation between DFT/solid-state and solution data. XB strength is only slightly affected by the PyNO oxygen properties [(atomic charge (Q), ionization energy (Is,min ) and local negative minima (Vs,min )], as the σ-hole (Vs,max ) of the donor halogen is the key determinant leading to the sequence N-halosaccharin>N-halosuccinimide>N-halophthalimide on the XB strength.
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Affiliation(s)
- Rakesh Puttreddy
- University of Jyvaskyla, Department of Chemistry, P.O. BOX 35, 40014, Jyväskylä, Finland
| | - J Mikko Rautiainen
- University of Jyvaskyla, Department of Chemistry, P.O. BOX 35, 40014, Jyväskylä, Finland
| | - Shilin Yu
- University of Jyvaskyla, Department of Chemistry, P.O. BOX 35, 40014, Jyväskylä, Finland
| | - Kari Rissanen
- University of Jyvaskyla, Department of Chemistry, P.O. BOX 35, 40014, Jyväskylä, Finland
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Sherard M, Dang QM, Reiff SC, Simpson JH, Leopold MC. On-Site Detection of Neonicotinoid Pesticides Using Functionalized Gold Nanoparticles and Halogen Bonding. ACS APPLIED NANO MATERIALS 2023; 6:8367-8381. [PMID: 37260915 PMCID: PMC10227770 DOI: 10.1021/acsanm.3c00618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Accepted: 04/10/2023] [Indexed: 06/02/2023]
Abstract
Neonicotinoid (NN) pesticides have emerged globally as one of the most widely used agricultural tools for protecting crops from pest damage and boosting food production. Unfortunately, some NN compounds, such as extensively employed imidacloprid-based pesticides, have also been identified as likely endangering critical pollinating insects like honey bees. To this end, NN pesticides pose a potential threat to world food supplies. As more countries restrict or prohibit the use of NN pesticides, tools are needed to effectively and quickly identify the presence of NN compounds like imidacloprid on site (e.g., in storage areas on farms or pesticide distribution warehouses). This study represents a proof-of-concept where the colloidal properties of specifically modified gold nanoparticles (Au-NPs) able to engage in the rare intermolecular interaction of halogen bonding (XB) can result in the detection of certain NN compounds. Density functional theory and diffusion-ordered NMR spectroscopy (DOSY NMR) are used to explore the fundamental XB interactions between strong XB-donor structures and NN compounds, with the latter found to possess multiple XB-acceptor binding sites. A fundamental understanding of these XB interactions allows for the functionalization of alkanethiolate-stabilized Au-NPs, known as monolayer-protected gold clusters (MPCs), with XB-donor capability (f-MPCs). In the presence of certain NN compounds such as imidacloprid, the f-MPCs subsequently exhibit visual XB-induced aggregation that is also measured with absorption (UV-vis) spectroscopy and verified with transmission electron microscopy (TEM) imaging. The demonstrated f-MPC-aggregation detection scheme has a number of favorable attributes, including quickly reporting the presence of the NN target, requiring only micrograms of suspect material, and being highly selective for imidacloprid, the most prevalent and most important NN insecticide compound. Requiring no instrumentation, the presented methodology can be envisioned as a simple screening test in which dipping a cotton swab of an unknown powder from a surface in a f-MPC solution causes f-MPCs to aggregate and yield a preliminary indication of imidacloprid presence.
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6
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Castro AC, Cascella M, Perutz RN, Raynaud C, Eisenstein O. Solid-State 19F NMR Chemical Shift in Square-Planar Nickel-Fluoride Complexes Linked by Halogen Bonds. Inorg Chem 2023; 62:4835-4846. [PMID: 36920236 PMCID: PMC10052355 DOI: 10.1021/acs.inorgchem.2c04063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Indexed: 03/16/2023]
Abstract
The halogen bond (XB) is a highly directional class of noncovalent interactions widely explored by experimental and computational studies. However, the NMR signature of the XB has attracted limited attention. The prediction and analysis of the solid-state NMR (SSNMR) chemical shift tensor provide useful strategies to better understand XB interactions. In this work, we employ a computational protocol for modeling and analyzing the 19F SSNMR chemical shifts previously measured in a family of square-planar trans NiII-L2-iodoaryl-fluoride (L = PEt3) complexes capable of forming self-complementary networks held by a NiF···I(C) halogen bond [Thangavadivale, V.; Chem. Sci. 2018, 9, 3767-3781]. To understand how the 19F NMR resonances of the nickel-bonded fluoride are affected by the XB, we investigate the origin of the shielding in trans-[NiF(2,3,5,6-C6F4I)(PEt3)2], trans-[NiF(2,3,4,5-C6F4I)(PEt3)2], and trans-[NiF(C6F5)(PEt3)2] in the solid state, where a XB is present in the two former systems but not in the last. We perform the 19F NMR chemical shift calculations both in periodic and molecular models. The results show that the crystal packing has little influence on the NMR signatures of the XB, and the NMR can be modeled successfully with a pair of molecules interacting via the XB. Thus, the observed difference in chemical shift between solid-state and solution NMR can be essentially attributed to the XB interaction. The very high shielding of the fluoride and its driving contributor, the most shielded component of the chemical shift tensor, are well reproduced at the 2c-ZORA level. Analysis of the factors controlling the shielding shows how the highest occupied Ni/F orbitals shield the fluoride in the directions perpendicular to the Ni-F bond and specifically perpendicular to the coordination plane. This shielding arises from the magnetic coupling of the Ni(3d)/F(2p lone pair) orbitals with the vacant σNi-F* orbital, thereby rationalizing the very highly upfield (shielded) resonance of the component (δ33) along this direction. We show that these features are characteristic of square-planar nickel-fluoride complexes. The deshielding of the fluoride in the halogen-bonded systems is attributed to an increase in the energy gap between the occupied and vacant orbitals that are mostly responsible for the paramagnetic terms, notably along the most shielded direction.
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Affiliation(s)
- Abril C. Castro
- Hylleraas
Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo, 0315 Oslo, Norway
| | - Michele Cascella
- Hylleraas
Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo, 0315 Oslo, Norway
| | - Robin N. Perutz
- Department
of Chemistry, University of York, Heslington, YO10 5DD York, United Kingdom
| | | | - Odile Eisenstein
- Hylleraas
Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo, 0315 Oslo, Norway
- ICGM,
Université Montpellier, CNRS, ENSCM, 34090 Montpellier, France
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7
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Weiss R, Aubert E, Groslambert L, Pale P, Mamane V. Chalcogen Bonding with Diaryl Ditellurides: Evidence from Solid State and Solution Studies. Chemistry 2022; 28:e202200395. [DOI: 10.1002/chem.202200395] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Indexed: 12/14/2022]
Affiliation(s)
- Robin Weiss
- Institute of Chemistry of Strasbourg, UMR 7177 - LASYROC CNRS and Strasbourg University 4 rue Blaise Pascal 67000 Strasbourg France
| | | | - Loic Groslambert
- Institute of Chemistry of Strasbourg, UMR 7177 - LASYROC CNRS and Strasbourg University 4 rue Blaise Pascal 67000 Strasbourg France
| | - Patrick Pale
- Institute of Chemistry of Strasbourg, UMR 7177 - LASYROC CNRS and Strasbourg University 4 rue Blaise Pascal 67000 Strasbourg France
| | - Victor Mamane
- Institute of Chemistry of Strasbourg, UMR 7177 - LASYROC CNRS and Strasbourg University 4 rue Blaise Pascal 67000 Strasbourg France
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8
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Dang QM, Gilmore ST, Lalwani K, Conk RJ, Simpson JH, Leopold MC. Monolayer-Protected Gold Nanoparticles Functionalized with Halogen Bonding Capability─An Avenue for Molecular Detection Schemes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:4747-4762. [PMID: 35385292 DOI: 10.1021/acs.langmuir.2c00381] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The use of functionalized nanoparticles (NPs) and their aggregation in the presence of a targeted analyte is a well-established molecular detection strategy predicated on harnessing specific molecular interactions to the NP periphery. Molecules able to specifically interact with the functionalized NPs alter the unique optical and electrochemical properties of the NPs as a function of interparticle spacing. While many intermolecular interactions have been successfully exploited in this manner in conjunction with aqueous NP systems, the use of non-aqueous NPs in the same capacity is significantly less explored. A fundamental interaction that has not been previously investigated in NP schemes is halogen bonding (XB). XB is an orthogonal, electrostatic interaction between a region of positive electrostatic potential (δ+) on a halogen atom (i.e., XB donor) and a negative (δ-) Lewis base (XB acceptor) molecule. To couple XB with NP systems, ligands featuring a molecular structure that promotes XB interactions need to be identified, optimized, and synthesized for subsequent attachment to NPs. Herein, density functional theory (DFT) and NMR techniques are used to identify a strong XB-donor moiety (-C6F4I) and a synthetic scheme for a thiolate ligand featuring that functionality is devised and executed with high purity/yield (78%). Ligand-exchange reactions allow functionalization of non-aqueous alkanethiolate-protected gold NPs or monolayer-protected clusters (MPCs) with the XB-donor ligands. Functionalized MPCs (f-MPCs), within both assembled films and in solution, are shown to engage in XB interactions with target XB-acceptor molecules. Molecular recognition events, including induced aggregation of the f-MPCs, are characterized with UV-vis spectroscopy, cyclic voltammetry, TEM imaging, and diffusion-ordered spectroscopy NMR with limits of detection of 50-100 nM for strong XB acceptors. While fundamental exploration of XB interactions is ongoing, this study represents a step toward utilizing XB within molecular detection schemes, an application with implications for supramolecular chemistry, forensic, and environmental chemical sensing.
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Affiliation(s)
- Quang Minh Dang
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Samuel T Gilmore
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Karthik Lalwani
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Richard J Conk
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Jeffrey H Simpson
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Michael C Leopold
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
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9
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Wojtkowiak K, Jezierska A, Panek JJ. Revealing Intra- and Intermolecular Interactions Determining Physico-Chemical Features of Selected Quinolone Carboxylic Acid Derivatives. Molecules 2022; 27:2299. [PMID: 35408698 PMCID: PMC9000753 DOI: 10.3390/molecules27072299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2022] [Revised: 03/24/2022] [Accepted: 03/30/2022] [Indexed: 02/04/2023] Open
Abstract
The intra- and intermolecular interactions of selected quinolone carboxylic acid derivatives were studied in monomers, dimers and crystals. The investigated compounds are well-recognized as medicines or as bases for further studies in drug design. We employed density functional theory (DFT) in its classical formulation to develop gas-phase and solvent reaction field (PCM) models describing geometric, energetic and electronic structure parameters for monomers and dimers. The electronic structure was investigated based on the atoms in molecules (AIM) and natural bond orbital (NBO) theories. Special attention was devoted to the intramolecular hydrogen bonds (HB) present in the investigated compounds. The characterization of energy components was performed using symmetry-adapted perturbation theory (SAPT). Finally, the time-evolution methods of Car-Parrinello molecular dynamics (CPMD) and path integral molecular dynamics (PIMD) were employed to describe the hydrogen bond dynamics as well as the spectroscopic signatures. The vibrational features of the O-H stretching were studied using Fourier transformation of the autocorrelation function of atomic velocity. The inclusion of quantum nuclear effects provided an accurate depiction of the bridged proton delocalization. The CPMD and PIMD simulations were carried out in the gas and crystalline phases. It was found that the polar environment enhances the strength of the intramolecular hydrogen bonds. The SAPT analysis revealed that the dispersive forces are decisive factors in the intermolecular interactions. In the electronic ground state, the proton-transfer phenomena are not favourable. The CPMD results showed generally that the bridged proton is localized at the donor side, with possible proton-sharing events in the solid-phase simulation of stronger hydrogen bridges. However, the PIMD enabled the quantitative estimation of the quantum effects inclusion-the proton position was moved towards the bridge midpoint, but no qualitative changes were detected. It was found that the interatomic distance between the donor and acceptor atoms was shortened and that the bridged proton was strongly delocalized.
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Affiliation(s)
| | - Aneta Jezierska
- Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland;
| | - Jarosław J. Panek
- Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland;
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Scheiner S, Hunter S. Influence of Substituents in the Benzene Ring on the Halogen Bond of Iodobenzene with Ammonia. Chemphyschem 2022; 23:e202200011. [PMID: 35099849 DOI: 10.1002/cphc.202200011] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Revised: 01/30/2022] [Indexed: 11/11/2022]
Abstract
The effects on the CI··N halogen bond between iodobenzene and NH3 of placing various substituents on the phenyl ring are monitored by quantum calculations. Substituents R = N(CH3)2, NH2, CH3, OCH3, COCH3, Cl, F, COH, CN, and NO2 were each placed ortho, meta, and para to the I. The depth of the σ-hole on I is deepened as R became more electron-withdrawing which is reflected in a strengthening of the halogen bond, which varied between 3.3 and 5.5 kcal/mol. In most cases, the ortho placement yields the largest perturbation, followed by meta and then para, but this trend is not universal. Parallel to these substituent effects is a progressive lengthening of the covalent C-I bond. Formation of the halogen bond reduces the NMR chemical shielding of all three nuclei directly involved in the C-I··N interaction. The deshielding of the electron donor N is most closely correlated with the strength of the bond, as is the coupling constant between I and N, so both have potential use as spectroscopic measures of halogen bond strength.
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Affiliation(s)
- Steve Scheiner
- Utah State University, Department of Chemistry and Biochemistry, 0300 Old Main Hill, 84322-0300, Logan, UNITED STATES
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