Through-bond Coupling Research Articles

Application of the Parity Rule of Through-Bond Coupling to the Design of "Superbridges" That Exhibit Greatly Enhanced Electronic Coupling

Application of the Parity Rule of Through-Bond Coupling to the Design of "Superbridges" That Exhibit Greatly Enhanced Electronic Coupling

The Central Bond Length in 1,2-Diarylethanes

The Central Bond Length in 1,2-Diarylethanes

Long CC single bonds in anthracene dimers: The structure of bi(anthracene-9,10-dimethylene) photodimer is redetermined

Ab Initio HF and DF Theory computations are performed on anthracene dimers 1–3 Crystal structures are redetermined at low temperature for 2 and 3. The 1.77 Å central bond length previously reported for 3 is shown to be only 1.648 Å. Through-bond coupling as a primary cause of bond lengthening in 1–3 is questioned.

Poly(phenylenevinylene) Bearing Built-in tert-Butylnitroxide. A Polyradical Ferromagnetically Coupled in the Intrachain

Abstract Poly(1,4- or 1,2-phenylenevinylene)s bearing a 2- or 4-substituted nitroxide radical were synthesized by polymerizing [bromo[N-tert-butyl-N-(trialkylsiloxy)amino]]styrenes with a palladium catalyst. The polyradicals were chemically stable, and their ESR and SQUID measurements indicated an intramolecular and through-bond ferromagnetic coupling.

Why Is a Simple n-Alkyl Bridge More Efficient Than a Polynorbornyl Bridge at Mediating Through-Bond Coupling?

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTWhy Is a Simple n-Alkyl Bridge More Efficient Than a Polynorbornyl Bridge at Mediating Through-Bond Coupling?Michael J. Shephard, Michael N. Paddon-Row, and Kenneth D. JordanCite this: J. Am. Chem. Soc. 1994, 116, 12, 5328–5333Publication Date (Print):June 1, 1994Publication History Published online1 May 2002Published inissue 1 June 1994https://doi.org/10.1021/ja00091a043RIGHTS & PERMISSIONSArticle Views157Altmetric-Citations45LEARN 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 (670 KB) Get e-Alerts Get e-Alerts

Electronic coupling through saturated hydrocarbon bridges

Through-bond (TB) coupling between the chromophores of a series of polynorbornyldienes 1( n ), α,ω-diethynyl[ n]staffanes 2( n ), α,ω-divinyl[ n]staffanes 3( n ), and a series of all-trans, n-alkyl compounds, X-(CH 2) l -X, where X=H 2CC 4( n ), HCC 5( n ), OH 6( n ), SH 7( n ), and planar NH 2 8( n ), have been investigated using ab initio MO theory, with the 3–21G basis set, in the Koopmans' theorem approximation. A natural bond orbital (NBO) analysis of the n-alkyl compounds, 4( n )– 8( n ), shows that much of the variation of the TB electronic coupling among the different series is governed by the self-energy of the chromophore orbitals. This conclusion was surmised from “tuning” experiments in which the chromophore self-energies in the NBO Fock matrix of one system are replaced by those of a different chromophore. Analysis of the TB pathways shows that the tight binding (nearest neighbor) model is grossly inadequate in explaining TB orbital interaction behavior, and that intrabridge interactions that skip over one or more bridge bonds also need to be included for a realistic analysis. In addition, model Hamiltonian matrices, constructed using NBO Fock matrix elements, demonstrate the importance of “retracing” pathways.

Opto-Electric Molecules Studied by Time-Resolved Microwave Conductivity (Trmc)

Abstract Charge separation in the singlet and triplet excited states of donor-spacer-acceptor, DSA, molecules can be studied using the flash-photolysis time-resolved microwave conductivity (TRMC) technique. Highly dipolar, DSA states with microsecond lifetimes can result from Intersystem crossing and through-bond coupling for π-bond conjugated and sigma-bond separated donoracceptor compounds respectively.

ETS study of the negative ion states of bicyclo[1.1.1]pentane, and its mono- and di-ethynyl derivatives: through-bond coupling of π* orbitals mediated by the staffane bridge

Electron transmission spectroscopy was used to study the through-bond coupling capacity of the bicyclo[1.1.1]pentane bridge for π* orbitals. Electron attachment energies of 1.66 and 2.78 eV were measured for 1,3-diethynylbicyclo[1.1.1]pentane, resulting in a π* splitting of 1.1 eV. This is larger than the splitting of the π levels determined earlier by PES (0.68 eV) and indicates a sizeable through-bond coupling. To aid in the interpretation, attachment energies were also measured for bicyclo[1.1.1]pentane (5.35 eV), for 1,1′-bi(bicyclo[1.1.1]pentane) (4.29 and 5.92 eV), and for 1-ethynylbicyclo[1.1.1]pentane (2.41 and 5.02 eV). The results are interpreted with the aid of qualitative arguments and of AM1 and Hartree—Fock virtual orbital energies within the context of Koopmans' theorem. The bicyclopentane bridge has σ and σ* orbitals to interact with both the in-phase and out-of-phase combinations of the acetylenic π* orbitals, and the observed splitting is thus a measure of the difference of the couplings. A minimal basis set is inadequate to reproduce the size of the splitting and we conclude that the trough-space interaction of the p π-basis orbitals on the C 1 and C 3 carbon atoms of the bicyclo[1.1.1]pentane bridge plays an important role.

Tuning of through-bond electronic coupling by donor and acceptor substitutions in the [(NH 3) 5Ru—1,4-dicyanobenzene—Ru(NH 3) 5] 5+ complex

Through-ligand electronic coupling in the [(NH 3) 5Ru III—1,4-dicyanobenzene—Ru II(NH 3) 5] 5+ complex is calculated depending on the donor or acceptor grafted on the benzene. The coupling strength is first discussed, showing that through-dicyanobutadiene is larger than through-1,4-dicyanobenzene coupling. With this ligand, the largest electronic coupling is reached with a full 4NO 2 substitution on the benzene. Coupling through an asymmetric 2NO 22NH 2-substituted benzene is one order of magnitude lower. This large difference is interpreted using the number and position of the active ligand molecular orbitals relative to the d-ruthenium orbital.

CHLORANIL‐PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMERS and EFFECT OF MAGNESIUM PERCHLORATE

The photosensitized monomerization of the cyclobutane dimers of 1,3-dimethylthymine by p-chloranil was investigated by means of steady-state irradiation and laser-flash photolysis. Quantum yields for the monomerization are 0.34 for the cis,syn dimer, 0.39 for the trans,syn dimer, and much less than 10(-2) for the cis,anti isomer. Formation of the chloranil anion radical associated with quenching of triplet chloranil by the dimers demonstrates that electron transfer from dimers to triplet chloranil occurs to initiate the monomerization. Kinetic analysis suggested that the syn-dimer cation radicals undergo the ring cleavage at greater than or equal to 10(9) s-1 before escaping from the solvent cage, while the reactivity of the anti-dimer cation radical is very low. The different reactivities of the syn and anti dimer cation radicals are discussed in terms of through-bond coupling between the n orbitals of N(1) and N(1') involving the cyclobutane-ring sigma orbitals. In the cases of the syn-dimers, the sensitizer-dimer ion-radical pairs undergo the rapid geminate recombination that works as a major energy dissipating channel responsible for the lower-than-unity quantum yields. It has been found that the presence of Mg(ClO4)2 at 0.1 M enhances approximately 1.5 times either the monomerization of the syn dimers or the formation of the chloranil anion radical. A laser-flash photolysis study shows that Mg2+ forms a complex with either the triplet or the anion radical of chloranil. The net salt effects are attributed to the retardation of the rapid geminate recombination by the participation of Mg2+ in the sensitizer-dimer ion-radical pairs.

Phosphorus-31 Fluorine-19 N.M.R. Through-Space Coupling

Abstract Through-space coupling, which may be observed when NMR active nuclei are close in space, is additive to any through-bond coupling. The magnitude of the coupling via the through-space mechanism varies according to the element, its valency and the distance between the coupled atoms-independently of the number of bonds separating the coupled atoms. The couplings between carbon-bound fluorine and phosphorus (in its three valent three coordinate state) have been studied using a series of 0-(trifluoromethyl)phenylphosphanes (1). The phosphorusfluorine coupling is lowest (29. 6Hz) for the primary phosphine (1, Y = H). It is 43 Ha for the diethylamino derivative (1, R = Et2N), rising to 53–56 Ha when Y is phenyl, heteroaromatic, alkyl and ethoxy groups, and then to 63 and 68 Hz for the phenoxy and fluoro derivatives. The PF coupling is largest (85–88 Hz) for the dichloro and dibromo compounds. The coupling constants are zero or close to aero for the corresponding salts, oxides and sulphides. The changes ...

Bridge-assisted electron transfer: effective electronic coupling

Nonadiabatic electron-transfer rates in intramolecular situations involving bridged structures intervening between donor and acceptor will generally be quite small in magnitude and will depend on the energetics of the transfer process, the chemical identity and nature of the donor, acceptor, and bridge species, the environment, and the temperature. We develop a self-contained perturbative method for the calculation of the electron-transfer matrix elements corresponding to intramolecular long-range electron transfer. This scheme is based on the Lippmann-Schwinger equation for the effective scattering matrix. Iteration of this perturbation equation easily yields such well-known results as the McConnell formula for long-range superexchange interactions, the competition of through-bond and through-space coupling in bridge structures, the identification of superexchange, the relationship of superexchange process to exponential decay at long distance and so forth.

A correlation between the rates of photoinduced long-range intramolecular electron transfer in rigidly linked donor-acceptor systems and computed π,π and π *,π * splitting energies in structurally related dienes

It has been found that the rates of photoinduced intramolecular electron transfer in a series of rigidly linked donor (dimethoxynaphthalene)-acceptor (dicyanovinyl) systems, in which the length and configuration of the hydrocarbon bridge are varied, correlate well with the computed Koopmans' theorem STO-3G π *,π * splitting energies in a structurally related series of dienes. It is proposed that the origin of this correlation lies in a through-bond coupling mechanism which obtains between the π * LUMOs of the chromophores and the bridge σ and σ * orbitals in both series of molecules.

Structure and conformation of spin-labeled amino acids in frozen solutions determined by electron nuclear double resonance. 2. Methyl N-(2,2,5,5-tetramethyl-1-oxypyrrolinyl-3-carbonyl)-L-tryptophanate, a molecule with multiple conformations

The conformation of methyl N-(2,2,5,5-tetramethyl- l-oxypyrrolinyl-3-carbonyl)-~-tryptophanate in frozen solutions has been determined by application of electron nuclear double resonance (ENDOR) spectroscopy and computer-based molecular modeling. ENDOR spectra of methyl L-tryptophanate and of the corresponding methyl esters of 0-fluore and q24uorotryptophan acylated at the amino group with the spin-label 2,2,5,5-tetramethyl- 1 -oxypyrroline-3-carboxylic acid exhibited well-resolved resonance adsorptions from protons and fluorines of the amino acid moiety. The ENDOR shifts were shown to correspond to principal hyperfine coupling (hfc) components, from which the dipolar contributions were estimated to calculate electron-nucleus separations. The ENDOR data indicated that there are two distinct conformations of spin-labeled methyl tryptophanate, the relative populations of which were dependent on solvent polarity. Torsion angle search calculations constrained by the ENDOR data showed that the predominant conformation in methanol was similar to that of a classical g- rotamer (x, - -63') with a near perpendicular (x2 - +loso) orientation of the indole ring. The second conformer was characterized by x, - -95' and x2 - -1 05O, indicative of an antiperpendicular orientation. In chloroform/toluene only the antiperpendicular conformer was detected. The different solvent-dependent orientations of the indole ring with respect to the nitroxyl group are explained on the basis of dipolar interactions of the aromatic side chain with solvent and with the peptide bond. The structure and conformation of amino acids and peptides in solution are of considerable importance in biophysical studies since the distribution of the side-chain dihedral angles is far from random and preferred conformations of amino acid side chains are frequently observed in proteim2 In general, the conforma- tional analysis of amino acid and peptide derivatives in solution has been carried out on the basis of circular dichroism, infrared spectroscopy, nuclear magnetic resonance (NMR3), and potential energy calculations. Analysis of direct structural data obtained by NMR methods depends primarily on estimates of the vicinal, through-bond coupling constants of H with the peptide amide proton HN or on estimates of coupling constants of protons bonded to adjacent carbons along the side chain.4 Reliable estimates of

Phosphorus-31 Fluorine-19 N.M.R. Through-Space Coupling

Abstract Through-space coupling, which may be observed when NMR active nuclei are close in space, is additive to any through-bond coupling. The magnitude of the coupling via the through-space mechanism varies according to the element, its valency and the distance between the coupled atoms-independently of the number of bonds separating the coupled atoms. The couplings between carbon-bound fluorine and phosphorus (in its three valent three coordinate state) have been studied using a series of 0-(trifluoromethyl)phenylphosphanes (1). The phosphorusfluorine coupling is lowest (29. 6Hz) for the primary phosphine (1, Y = H). It is 43 Ha for the diethylamino derivative (1, R = Et2N), rising to 53–56 Ha when Y is phenyl, heteroaromatic, alkyl and ethoxy groups, and then to 63 and 68 Hz for the phenoxy and fluoro derivatives. The PF coupling is largest (85–88 Hz) for the dichloro and dibromo compounds. The coupling constants are zero or close to aero for the corresponding salts, oxides and sulphides. The changes in the magnitude of the phoaphane couplings are discussed in terms of conformational and electronic influences on a through-space spin-spin coupling mechanism.

Through-bond modulation of intramolecular electron transfer in rigidly linked donor-acceptor systems

Photoinduced electron transfer rates are reported for a pair of rigid bichromophoric molecules, 1(8) and 3(8), in a variety of solvents. It was found that intramolecular electron transfer in 1(8) is up to five times faster than in 3(8). X-ray crystallography revealed that the cyclopentyl ring attached to the dicyanoethylene group is “flatter” in 3(8) compared to 1(8), and this results in diminished through-bond coupling in 3(8) compared to 1(8). This conclusion is reinforced by the observation that the calculated through-bond π, π and π * interaction energies in dienes 7(6) and 9(6) are larger than those in the dienes 8(6) and 10(6), respectively.

Molecular Structures of Diarylcyclobutanes Associated with Reactivities in Ring-Cleavage Reactions: Implications of Conformationally Controlled Through-Bond Coupling

Abstract Molecular structures of diarylcyclobutanes (1–6) have been determined by single-crystal X-ray analyses. Although the distances and angles of the cyclobutane rings are relatively normal, the torsional angles between the aryl ring and the plane involving the ipso carbon and the aryl-substituted carbons of cyclobutane ring are close to 90° in cases of 1–4, but very small (2.3–11.3°) in cases of 5 and 6; conformations of the aryl substituents are highly restricted by the rigid tricyclic structure or by nonbonding interactions between the vicinal substituents in the cis configuration. Restricted conformations are closely related to the different reactivities of the cyclobutane in photochemical, thermal, and radiation-induced ring-splitting reactions. The structure-reactivity relationships are discussed in terms of the conformation-controlled π–σ orbital interactions associated with the capabilities of the π electron systems in through-bond coupling.

A unique lithium halide complex, [(LiBr)2·3HMPA·toluene]: synthesis from reaction of solid NH4Br with BunLi in HMPA (hexamethylphosphoramide)/toluene media, crystal structure showing two Li–Br units linked by three µ2-HMPA ligands, and detection of7Li ⋯31P coupling in solutions of the complex

Reaction of solid NH4Br with BunLi and HMPA (hexamethylphosphoramide)(1 : 1 : 2 ratio) in toluene produces (LiBr)2·3HMPA·toluene, (1), shown by X-ray crystallography to contain (LiBr)2·3HMPA molecules whose two terminal Li–Br units are linked by three µ2-HMPA ligands and with toluene molecules lying between these units in the lattice; in arene solutions, the (LiBr)2·3HMPA units remain intact, giving rise in 7Li n.m.r. spectra to 1 : 3 : 3 : 1 quartets caused by through-bond (OP) coupling of each 7Li nucleus to three 31P(HMPA) centres.

Electron transfer via dithiaspiroalkane linkages. Nature of long-range through-bond electronic coupling in disulfoxide radical cations and bis(metal) complexes and implications for the characterization of the sulfoxide bond

Electron transfer via dithiaspiroalkane linkages. Nature of long-range through-bond electronic coupling in disulfoxide radical cations and bis(metal) complexes and implications for the characterization of the sulfoxide bond

Low-temperature neutron powder diffraction study of chromium dioxide and the validity of the Jahn-Teller viewpoint

The structure of CrO{sub 2} has been determined at 10, 173, and 295 K by powder neutron diffraction. The structure of this material is interesting because the mode of distortion around the metal center is the reverse of that expected on the basis of local Jahn-Teller considerations. Band-structure calculations however, show that although the structure with two long and four short metal-oxygen distances is that expected for the d{sup 0} configuration, where O-O repulsions control the picture, the opposite distortion is predicted for d counts leading to t{sub 2g} block degeneracies. We explain this result by constructing the d band dispersion curve using the angular overlap model. It is shown how through-bond coupling in the lower than octahedral local environment allows mixing between a component of each of the e{sub g} and t{sub 2g} orbital sets and frustrates the energetic preferences predicted for the t{sub 2g} block alone. The factors that control the details of the geometries of the transition-metal oxides and fluorides with the rutile structure are explored. 35 refs., 7 figs., 5 tabs.