Bent Bonds Research Articles

Stereoelectronic effects, tau bonds, and Cram's rule

Review of stereoelectronic effects and outline of the suggestion that the bent bond (tau bond) be used as a model for the double bond.

Are there pi bonds in benzene?

The wave function of benzene may be described in terms of two components corresponding to the Kekul\'e structures. Theoretical evidence is presented which indicates that the optimal orbitals comprising these structures form alternating single bonds and double bent bonds rather than the conventional \ensuremath{\sigma} and \ensuremath{\pi} bonds. Ab initio calculations which incorporate electronic correlation effects and explicitly treat resonance demonstrate that the bent-bond description is energetically the better representation of the ground state.

ChemInform Abstract: Microwave Spectra and Structure of 1,2‐Dichlorobenzene‐3d and ‐4d.

Abstract The microwave spectra of six monodeuterated 1,2-dichlorobenzenes-3 d and -4 d , each having 1,2- 35 Cl 2 , 1,2- 35 Cl 37 Cl, or 1,2- 37 Cl 35 Cl, in the frequency range 10–40 GHz, have been analyzed. The r 0 -structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r 0 bond lengths (A) and bond angles (degrees) are as follows: r CC = 1.393–1.398; r CH = 1.080–1.083; r CCl = 1.729(15); ∠CCC = 119.5–120.3; ∠C(1)C(2)Cl(2) = 120.9(5); ∠C(2)C(3)H(3) = 118.7(11); and ∠C(3)C(4)H(4) = 119.5(13). The following distortions in the structure are found. The distortion of the benzene ring is of the same extent as in chlorobenzene and rather smaller than in fluorobenzenes. On the other hand, the two CCl bonds bend outwards from each other by about 1° and the ortho -hydrogen H(3) by 0.6° towards the Cl atom, respectively, from the bisector at the ipso -carbon. The ortho -hydrogen is closer to the chlorine atom. The possibility of a “bent bond” in the CCl has been inspected from the nuclear quadrupole coupling constants of chlorine nuclei.

Polyhedral hybrid approach to bonding in molecules containing transition metals

A polyhedral hybrid approach, based on generalized valence bond theory, is proposed to treat the electronic structure and bonding in transition metal molecules. A key feature of the approach is the ubiquity of “bent bonds” formed from overlapping hybrid orbitais.

New Theoretical Description of the Carbon-Carbon Triple Bond

We present new theoretical results on the carbon-carbon triple bond which suggests that such may be better described in terms of bent bonds than by the traditional combination of $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ bonds. By use of correlated wave functions such behavior is explicitly demonstrated for difluoroacetylene. These represent the first quantitative calculations which document a case where a triple bent-bond description is energetically favored over a $\ensuremath{\sigma}\ensuremath{-}\ensuremath{\pi}$ description.

Microwave spectra and structure of 1,2-dichlorobenzene-3 d and -4 d

The microwave spectra of six monodeuterated 1,2-dichlorobenzenes-3 d and -4 d, each having 1,2- 35Cl 2, 1,2- 35Cl 37Cl, or 1,2- 37Cl 35Cl, in the frequency range 10–40 GHz, have been analyzed. The r 0-structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r 0 bond lengths (Å) and bond angles (degrees) are as follows: r CC = 1.393–1.398; r CH = 1.080–1.083; r CCl = 1.729(15); ∠CCC = 119.5–120.3; ∠C(1)C(2)Cl(2) = 120.9(5); ∠C(2)C(3)H(3) = 118.7(11); and ∠C(3)C(4)H(4) = 119.5(13). The following distortions in the structure are found. The distortion of the benzene ring is of the same extent as in chlorobenzene and rather smaller than in fluorobenzenes. On the other hand, the two CCl bonds bend outwards from each other by about 1° and the ortho-hydrogen H(3) by 0.6° towards the Cl atom, respectively, from the bisector at the ipso-carbon. The ortho-hydrogen is closer to the chlorine atom. The possibility of a “bent bond” in the CCl has been inspected from the nuclear quadrupole coupling constants of chlorine nuclei.

Theoretical evidence for “bent bonds” in the co 2 molecule

Ab initio correlated wavefunction results for the CO 2 molecule are presented, which strongly suggest that the carbon-oxygen double bonds in the molecule are better represented in terms of a pair of “bent bonds” than by a combination of a σ-bond and a π-bond.

Point charges and the molecular electrostatic potential

Abstract The topological features of the bare nuclei potential are described in detail. The significance of the impossibility of it having a minimum is discussed. The molecular electrostatic potential and its representation using point charges is then described. The need to have some charges off the nuclei to represent lone pairs and bent bonds is emphasized

ChemInform Abstract: THEORETICAL DETERMINATION OF MOLECULAR STRUCTURE AND CONFORMATION. 15. THREE‐MEMBERED RINGS: BENT BONDS, RING STRAIN, AND SURFACE DELOCALIZATION

Chemischer InformationsdienstVolume 16, Issue 42 Physical Organic Chemistry ChemInform Abstract: THEORETICAL DETERMINATION OF MOLECULAR STRUCTURE AND CONFORMATION. 15. THREE-MEMBERED RINGS: BENT BONDS, RING STRAIN, AND SURFACE DELOCALIZATION D. CREMER, D. CREMERSearch for more papers by this authorE. KRAKA, E. KRAKASearch for more papers by this author D. CREMER, D. CREMERSearch for more papers by this authorE. KRAKA, E. KRAKASearch for more papers by this author First published: October 22, 1985 https://doi.org/10.1002/chin.198542057AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue42October 22, 1985 RelatedInformation

Theoretical determination of molecular structure and conformation. 15. Three-membered rings: bent bonds, ring strain, and surface delocalization

Energy, geometry, one-electron density distribution, and Laplace concentrations of cyclopropane (l), aziridine (2), oxirane (3), cyclopropyl anion (4), protonated aziridine (5), protonated oxirane (6), halogen-bridged fluoroethyl cation (7), and hydrogen-bridged ethyl cation (8) are investigated and compared with their corresponding alicyclic counterparts. The relationship between three-membered rings (3MR) and a-complexes is demonstrated by analyzing their electron density pattern with the aid of catastrophe theory. A continuous change from 3MRs to .rr-complexes can be observed if the acceptor (donor) ability of a group X interacting with an ethylene unit is increased (decreased). The bend of the 3MR bonds is described by the curvature of the paths of maximum electron density linking the ring atoms. Interpath angles are used to evaluate the strain energy of a 3MR. A value of 75 kcal/mol is found for 1. Strain is partially compensated by stabilizing effects arising from surface delocalization of cr-electrons of the 3MR (48 kcal/mol for 1). Both ring strain and surface delocalization increase in the series 1, 2, 3 with a slight dominance of the former effect. The chemical relevance of theoretical results is discussed with regard to the ability of 3MRs to interact with mystems and to undergo addition reactions with electrophiles and nucleophiles. The observed regioselectivity in ring-opening reactions of oxiranes is explained.

Bent bonds in four-membered rings

Bent bonds in four-membered rings

A comparative study of bent-bond vs. Walsh model in strained systems. Bicyclo(1.1.0)butane

Bent bond and Walsh models for the electronic structure of the highly strained bicyclo(1.1.0)butane were critically examined and compared with the available PE spectrum. It is found that the bent bond scheme is by far more superior to the widely used Walsh semilocalized molecular orbitals. Hence the local hybrid orbitals provide a useful aid in assigning and interpreting of PE spectra. Present results lend support to the hybrid model in bicyclo(1.1.0)butane proposed by Schulman.

Charge density distribution in small strained rings. A local hybrid overlap study

The local hybrid orbitals obtained by the iterative maximum overlap method were used to construct electron isopycnic (isodensity) maps and deformation contours in strained cyclopropane, cyclopropene, cyclobutene and cyclopentadiene rings. The qualitative features of electron charge distributions and reorganization effects accompanying formation of chemical bonds are fairly well reproduced. The isopycnic maps and the corresponding deformation diagrams reflect the presence of bent bonds. They also indicate that the Förster—Coulson—Moffitt bent bond picture of strained rings is in principle equivalent to the Walsh model. Summarizing present results and earlier findings one can say that variable hybridization provides a simple, clear semiempirical model of covalent bonding.

Hindered rotation of the isopropenyl group in substituted isopropenylcyclohexanes and identification of preferred rotamers by nuclear magnetic resonance. Bent bonds may be better bonds

Hindered rotation of the isopropenyl group in substituted isopropenylcyclohexanes and identification of preferred rotamers by nuclear magnetic resonance. Bent bonds may be better bonds

Infrared and raman spectra of barium nitrite monohydrate

The low temperature infrared absorption and room temperature laser Raman spectra of polycrystalline Ba(NO 2) 2 · H 2O and its deuterated analogue are studied. The strongly bonded H-atom of the water molecule makes a highly bent H-bond while the weakly bonded H-atom exhibits a slightly bent (or possible bifurcated) bond consistent with recent structural data; the H-bond enthalpies are estimated to be 3.3 and 2.1 KCal mole respectively. The wagging, twisting and rocking modes of the water molecule have been assigned using several well known criteria. The force constants of these modes have also been computed. The librational splittings observed at low temperature are consistent with polarization data, and are being attributed to infrared active factor group components.

Hydrazonium(2+) hexafluorosilicate, N2H6SiF6: a NaCl-type structure with two-dimensional hydrogen-bonding networks

Hydrazonium(2+) hexafluorosilicate, N2H6SiF6, at room temperature has an orthorhombic (Pbca, Z = 4), pseudotetragonal unit cell (a = 7.605(1) Å, b = 7.586(2) Å, c = 8.543(1) Å). The structure consists of centrosymmetric N2H62+ and SiF62− ions arranged in a NaCl-type packing and connected by hydrogen bonds to two-dimensional N2H6–SiF6 layers parallel to (001). All H atoms are engaged in hydrogen bonding. Four of the six [Formula: see text] bonds to each cation are normal but significantly bent; the other two are trifurcated, [Formula: see text], but the out-of-layer component of the trifurcated bond is relatively unimportant. The N2H6SiF6 structure is compared in some detail with the structures of other hydrazonium(2+) salts, with particular attention to the N—N bond length, to the "effective" size of the N2H62+ ion, and to the tendency of this ion to form bent hydrogen bonds.

Electrostatic potentials of strained systems: nitrocyclopropane

The presence of an NO 2 substituent is found to eliminate the negative electrostatic potentials associated with the “bent” CC bonds cyclopropane. This is presumably due in large part to a rearrangement of electronics charge caused by the nitro group, as is shown by electronic density difference plots. Bond path calculations reveal bent bonds in nitrocyclopropane that are very similar to those in cycloprophane.

Presence of a substantially bent iridium-iridium bond in Ir2O(PPh3)2(NO)2

Presence of a substantially bent iridium-iridium bond in Ir2O(PPh3)2(NO)2

ChemInform Abstract: INTERPRETATION OF BOND LENGTH DATA FOR TRANSITION METAL‐ACETYLENE COMPLEXES, IN PARTICULAR THE COMPLEX (C5H5NH)(TACL4(PHCCPH)(NC5H5))

Chemischer InformationsdienstVolume 13, Issue 9 Physical Organic Chemistry ChemInform Abstract: INTERPRETATION OF BOND LENGTH DATA FOR TRANSITION METAL-ACETYLENE COMPLEXES, IN PARTICULAR THE COMPLEX (C5H5NH)(TACL4(PHCCPH)(NC5H5)) E. A. ROBINSON, E. A. ROBINSONSearch for more papers by this author E. A. ROBINSON, E. A. ROBINSONSearch for more papers by this author First published: March 2, 1982 https://doi.org/10.1002/chin.198209063AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue9March 2, 1982 RelatedInformation

ChemInform Abstract: NATURAL HYBRID ORBITALS

From the information contained in the (exact or approximate) first-order density matrix, we describe a method for extracting a unique set of atomic hybrids and bond orbitals for a given molecule, thereby constructing its “Lewis structure” in an a priori manner. These natural hybrids are optimal in a certain sense, are efficiently computed, and seem to agree well with chemical intuition (as summarized, for example, in Bent’s Rule) and with hybrids obtained by other procedures. Using simple INDO-SCF-MO wave functions, we give applications of the natural hybrid orbital analysis to molecules exhibiting a variety of bonding features, including lone pairs, multiple bonds, strained rings, and “bent bonds”, multiple resonance structures, hydrogen bonds, and three-center bonds. Three examples are described in greater detail: (i) “orbital following” during ammonia umbrella inversion, (ii) the dimerization of water molecules, and (iii) the hydrogen-bridged bonds of diborane.