Benzazole-N(SINGLE BOND)BH3 adducts. Reductive transposition of 2-benzimidazole, 2-benzothiazole,and 2-benzoxazole N(SINGLE BOND)BH3 adducts to 1,3,2-benzimidazaborole, 1,3,2-benzoxaborole,and 1,3,2-benzothiazaborole

1,3,2-Benzimidazaborole, 1,3,2-benzoxaborole, and 1,3,2-benzothiazaborole were synthesized from the corresponding 2-benzazole N(SINGLE BOND)BH₃ and 2-benzazole S(SINGLE BOND)BH₃ adducts through a reductive transposition from the isolobal fragment X(SINGLE BOND)C(sp²) (DOUBLE BOND) N(sp²) (SINGLE BOND) B(sp³) (X (DOUBLE BOND) N, O, S) to the fragment X(SINGLE BOND)B(sp²) (DOUBLE BOND) N(sp²) (SINGLE BOND) C(sp³). N(SINGLE BOND)BH₃ substitution shifts to lower frequencies 4-H, C-3a, and C-7a resonances. The X-ray diffraction analysis of 2-(o-methoxyphenyl)benzothiazole N(SINGLE BOND)BH₃ adduct is reported. Two new tetracyclic boron-bridged compounds were observed as by-products (6,9-(ethyl)-diaza-2-oxa-1-bora[3,4,7,8]-dibenzobycyclo[4.3.0]-nona-3,7-diene, 6d, and 8-aza-9-oxa-2-thia-1-bora-[3,4,7,8]dibenzobycyclo[3.4.0]nona-3,7-diene, 15d, when 2-(o-methoxyphenyl)-1-ethylbenzimidazole-BH₃ 6b and 2-(o-methoxyphenyl)-benzothiazole-BH₃ 15b adducts were heated. © 1996 John Wiley & Sons, Inc.     

π-Bonding contribution to restricted internal rotations in saccharides

Extensive semiempirical SCF-MO calculations confirm that the exo-anomeric effect in methyl O-, N- and S-glycosides deals with an interaction of π-character along the C₁(SINGLE BOND)Y₁ bond in a X₅(SINGLE BOND)C₁(SINGLE BOND)Y₁(SINGLE BOND)Me moiety (where X = O, S; Y = O, NH, S). The bond-order between orbitals of pπ symmetry on C₁ and Y₁ serves as a measure of all significant molecular orbital interactions responsible for the exo-anomeric stabilization. The set of simpler compounds X(SINGLE BOND)CH₂(SINGLE BOND)Y (X = OH, SH, SeH, TeH; Y = OH, SH, SeH, TeH, NH₂) on which the anomeric effect has been well studied was also calculated and it is noticeable that the π-bond-orders accord with the results of other analyses of the ab initio wave function accounting for the anomeric effect. Although the AM1 and the PM3 parameterizations of MNDO do not accurately reproduce the anomeric effect energetic, they do reproduce accordingly the expected variations in the molecular conformations of complex carbohydrates, and thus it follows that there are maximal π-bond-orders for the synclinal arrangement around the C₁(SINGLE BOND)Y₁ bond. In addition, the π-bond-orders show the same behavior for conformational preferences around the C₁(SINGLE BOND)C′₁ and the C₅(SINGLE BOND)C₆ bonds in methyl C-glycosides and in the hydroxymethyl group of α-D -glucose, respectively. © 1996 by John Wiley & Sons, Inc.     

The hydroxyl radical reaction rate constant and products of ethyl 3-ethoxypropionate

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of ethyl 3-ethoxypropionate (EEP, CH₃CH₂(SINGLE BOND)O(SINGLE BOND)CH₂CH₂C(O)O(SINGLE BOND)CH₂CH₃). EEP reacts with OH with a bimolecular rate constant of (22.9±7.4)×10⁻¹² cm³ molecule⁻¹s⁻¹ at 297±3 K and 1 atmosphere total pressure. In order to more clearly define EEP's atmospheric reaction mechanism, an investigation into the OH+EEP reaction products was also conducted. The OH+EEP reaction products and yields observed were: ethyl glyoxate (EG, 25±1% HC((DOUBLE BOND)O)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl (2-formyl) acetate (EFA, 4.86±0.2%, HC((DOUBLE BOND)O)(SINGLE BOND)CH₂(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl (3-formyloxy) propionate (EFP, 30±1%, HC((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₂(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl formate (EF, 37±1%, HC((DOUBLE BOND)O)O(SINGLE BOND)CH₂CH₃), and acetaldehyde (4.9±0.2%, HC((DOUBLE BOND)O)CH₃). Neither the EEP's OH rate constant nor the OH/EEP reaction products have been previously reported. The products' formation pathways are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. © 1997 John Wiley & Sons, Inc.     

A density functional study of Fe(SINGLE BOND)N2, Fe(SINGLE BOND)N+2, and Fe(SINGLE BOND)N−2

The interaction of an iron atom with molecular nitrogen was studied using density functional theory. Calculations were of the all-electron type and both conventional local and gradient-dependent models were used. A ground state of linear structure was found for Fe(SINGLE BOND)N₂, with 2S + 1 = 3, whereas the triangular Fe(SINGLE BOND)N₂ geometry, of C_2v symmetry, was located 2.1 kcal/mol higher in energy, at least for the gradient-dependent model. The reversed order was found using the conventional local approximation. In Fe(SINGLE BOND)N₂, the N(SINGLE BOND)N bond is strongly perturbed by the iron atom: It has a bond order of 2.4, a vibrational frequency of 1886 cm⁻¹, and an equilibrium bond length of 1.16 Å: These values are 3.0, 2359 cm⁻¹, and 1.095 Å, respectively, for the free N₂ molecule. With the gradient-dependent model and corrections for nonsphericity of the Fe atom, a very small binding energy, 8.8 kcal/mol, was calculated for Fe(SINGLE BOND)N₂. Quartet ground states were found for both Fe(SINGLE BOND)N⁺₂ and Fe(SINGLE BOND)N⁻₂. The adiabatic ionization potential, electron affinity, and electronegativity were also computed; the predicted values are 7.2, 1.22, and 4.2 eV, respectively. © 1997 John Wiley & Sons, Inc.     

G2 ab initio calculations on three-membered rings: Role of hydrogen atoms

G2 ab initio calculations on all ABX three-membered rings (TMRs) that can be derived from cyclopropane by systematic substitution of the (SINGLE BOND)CH₂ groups by (SINGLE BOND)NH or (SINGLE BOND)O groups have been performed. Our results show that the decrease in the A(SINGLE BOND)B bond length as the electronegativity of X increases is significantly larger than that found for the corresponding acyclic analogs. In general, a systematic substitution of the (SINGLE BOND)CH₂ groups of cyclopropane by (SINGLE BOND)NH or (SINGLE BOND)O groups implies significant geometric changes that are not reflected in a parallel change of the corresponding conventional ring strain energy (CRSE). When the electronegativity of the groups forming the TMR increases the effect on the CRSE of the system is small, although the charge delocalization inside the ring decreases. The near constancy of the CRSE along the series can be explained in terms of the charge redistribution of the system where the (SINGLE BOND)CH₂ groups play a crucial role. There are, however, significant changes in the hydrogenation energies of the TMR investigated; our results show that, when in an ABX three-membered ring, the electronegativity of X increases the hydrogenation energy of A(SINGLE BOND)B bond decreases and vice versa. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1072–1086, 1998     

Synthesis and properties of polycarbosilanes with the meta-linkage bending unit by hydrosilylation polymerization

The polycarbosilanes (PCS) with meta-linkage bending unit ((SINGLE BOND)Me₂Si(SINGLE BOND)m(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)) were successfully synthesized in mild conditions by hydrosilylation in the presence of [Pt{(CH₂(DOUBLE BOND)CHSiMe₂)₂O}₂]. The PCS obtained were soluble in various solvents owing to the lowering of the crystallinity. These properties are well compared with those of the PCS [(SINGLE BOND)Me₂Si(SINGLE BOND)p(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)]_n. © 1996 John Wiley & Sons, Inc.     

Comparative study of BSSE correction methods at DFT and MP2 levels of theory

A comparative study of intermolecular potential energy curves is performed on the complexes H₂O(SINGLE BOND)HF, H₂O(SINGLE BOND)H₂O, H₂O(SINGLE BOND)H₂S, and H₂S(SINGLE BOND)H₂S using nine different basis sets at the MP2 and DFT (BLYP and B3LYP) levels of theory. The basis set superposition error is corrected by means of the counterpoise scheme and based on the “chemical Hamiltonian approach.” The counterpoise and CHA-corrected DFT curves are generally close to each other. Using small basis sets, the B3LYP functional cannot be favored against the BLYP one because the BLYP results sometimes get closer to the MP2 values than those of B3LYP. From the results—including the available literature data—we suggest that one has to use at least polarized-valence triple-zeta-quality basis sets (TZV, 6-311G) for the investigation of hydrogen-bonded complexes. Special attention must be paid to the physical nature of the binding. If the dispersion forces become significant DFT methods are not able to describe the interaction. Proper correction for the basis set superposition error is found to be mandatory in all cases. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 575–584, 1998     

Ab initio studies of three-membered ring formation through intramolecular nucleophilic substitution

Three-membered ring (3MR) forming processes of ⁻X(SINGLE BOND)CH₂(SINGLE BOND)CH₂(SINGLE BOND)F and ⁻CH₂(SINGLE BOND)C((SINGLE BOND)Y)(SINGLE BOND)CH₂(SINGLE BOND)F (X(DOUBLE BOND)CH₂, O, or S and Y(DOUBLE BOND)0 or S) through a gas phase neighboring group mechanism (S_Ni) are studied theoretically using the ab initio molecular orbital method with the 6–31+G* basis set. When electron correlation effects are considered, the activation (ΔG^≠) and reaction energies (ΔG⁰) are lowered by ca. 10 kcal mol⁻¹, indicating the importance of the electron correlation effect in these reactions. The contribution of entropy of activation (−TΔS^≠) at 298 K to ΔG^≠ is very small, and the reactions are enthalpy controlled. The ΔG^≠ and ΔG⁰ values for these ring closure processes largely depend on the stabilities of the reactants and the heteroatom acting as a nucleophilic center. The Bell–Evans–Polanyi principle applies well to all these reaction series. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1773–1784, 1997     

Cyanide adsorbed on coinage metal electrodes: A relativistic density functional investigation

The adsorptive properties of cyanide (CN⁻) on coinage metal (M) electrodes (M=Cu, Ag, Au) have been investigated using a relativistic density functional method. The way to model the electrochemical potential applied to the electrodes is to consider the systems in the presence of a perturbative external field F. The field-perturbative approach is proven to be a suitable method in interpreting the observed spectral shifts with electrode potential. The calculated potential-dependent shifts of ω_{M(SINGLE BOND)CN} and ω_{C(SINGLE BOND)M} are similar for the three metals, in agreement with experiment observations. The relativistic effects are required to account for the similarity in the frequency shifts of ω_{M(SINGLE BOND)CN}. The calculated vibrational tuning rates dω_{C(SINGLE BOND)N}/dF are 6.61×10⁻⁷, 6.61×10⁻⁷, and 5.64×10⁻⁷ cm⁻¹/(V/cm) for M=Cu, Ag, and Au, respectively. The coupling of the M(SINGLE BOND)CN and C(SINGLE BOND)N internal modes contributes significantly (about 25%) to the size of the frequency shifts Δω_{C(SINGLE BOND)N} of the ligand. The effect of electric fields on the metal(SINGLE BOND)CN⁻ bonding is also investigated. It is shown that changes in the magnitude of CN⁻ to the metal donation and M(SINGLE BOND)CN bond strength occur under the influence of the electric field. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 175–185, 1998     

Kinetic isotope effects on metaphosphate generation from fragmentation of 2,3-oxaphosphabicyclo[2.2.2]octene derivatives

Kinetic isotope effects of deuterium and oxygen-18 were measured on fragmentation of syn-3-ethoxy ( 1a ) and syn-3-(N,N-diethylamino) ( 1b ) 2,3-oxaphosphabicyclo[2.2.2]octene derivatives in 1,2-dichloroethane at 100°C. The secondary deuterium isotope effect on hydrogen adjacent to the P(SINGLE BOND)C bond was found to be 1.060 ± 0.008 for 1a and 1.081 ± 0.009 for 1b . The kinetic oxygen isotope effect on the bridge P(SINGLE BOND)O(SINGLE BOND)C is 0.9901 ± 0.0016 for 1a . The data indicate an unsymmetrical transition state for retrocycloaddition extrusion of the metaphosphate moiety, with the breakage of the C(SINGLE BOND)P bond and formation of the P (DOUBLE BOND) O bond more advanced than the C(SINGLE BOND)O breakage. A synthesis of 1a and 1b labeled with deuterium is described. © 1996 John Wiley & Sons, Inc.     

Internal conrotation and disrotation in H2BCH2BH2 and diborylmethane 1,3 H exchange

The paths of correlated internal disrotation (barrier less than 0.4 kcal/mol) and conrotation (barrier around 1.9 kcal/mol) of the two BH₂ groups in H₂BCH₂BH₂ have been computed employing ab initio [MP2(full)/6–31G**] and density functional theory (Becke3LYP/6–311+G**) methods. Two B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative interactions stabilize the C_s symmetric H₂BCH₂BH₂ isomer ( 1 ). The B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative stabilization, evaluated by homodesmotic reactions and using the orbital deletion procedure (which “deactivates” the “vacant” born p orbital), is less than 6 kcal/mol in diborylmethane. The B(SINGLE BOND)C(DOTTED BOND)B(p) stabilization is shown to be remarkably large in C₄B₆H₁₀ (Td). At MP2(fu)/6–31G**, disproportionation into 1 and methane is only 5.6 kcal/mol exothermic. The 1,3 H exchange in diborylmethane is an asynchronous process and proceeds via a doubly bridged cyclic intermediate with 9.3 kcal/mol barrier. Structures with “planar tetracoordinate” carbon are stabilized considerably by BH₂ substituents, but they are still high in energy. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1792–1803, 1997     

Polysulfonylamine. CLXXVIII Onium‐Salze des Benzol‐1,2‐di(sulfonyl)amins (HZ): Eine zweite Kristallform des Ammonium‐Salzes NH4Z·H2O und Kristallstruktur des Bis(triphenylphosphoranyliden)ammonium‐Salzes [Ph3PNPPh3]Z

Polysulfonylamines. CLXXVIII. Onium Salts of Benzene‐1,2‐di(sulfonyl)amine (HZ): A Second Crystal Form of the Ammonium Salt NH₄Z·H₂O and Crystal Structure of the Bis(triphenylphosphoranylidene)ammonium Salt [Ph₃PNPPh₃]Z A dimorphic form of NH₄Z·H₂O, where Z^? is N‐deprotonated ortho‐benzenedisulfonimide, has been obtained and structurally characterized (previously known form 1A : monoclinic, P2₁/c, Z′ = 1; new polymorph 1B : monoclinic, P2₁/n, Z′ = 1). Both structures are dominated by an abundance of classical hydrogen bonds N⁺–H/O–H···O=S/OH₂, whereby the anionic N^? function does not act as an acceptor. The major difference between the dimorphs arises from the topology of the hydrogen bond network, which is two‐dimensional in 1A , leading to a packing of discrete lamellar layers, but three‐dimensional in 1B . Moreover, the latter network is reinforced by a set of weak C–H··O/N hydrogen bonds, whereas the layered structure of 1A displays only one independent C–H···O bond, providing a link between adjacent layers. The compound [Ph₃PNPPh₃]Z ( 2 , monoclinic, P2₁/c, Z′ = 1) is the first structurally authenticated example of an ionic Z^? derivative in which the cation contains neither metal bonding sites nor strong hydrogen bond donors. This structure exhibits columns of anions, surrounded by four parallel columns of cations, giving a square array. The large cations are associated into a three‐dimensional framework via weak C–H···C(π) interactions and an offset face‐to‐face phenyl interaction, while the anions occupy tunnels in this framework and are extensively bonded to the surrounding cations by C–H···O/N^? hydrogen bonds and C–H···C(π) interactions.     

Estimates of the structure and dimerization energy of polyacetylene from ab initio calculations on finite polyenes

Ab initio calculations at the Hartree-Fock (HF) and the second-order Møller-Plesset (MP2) levels are performed for finite polyenes C_2nH_2n+2 to estimate the structure and dimerization energy (E_dim) of polyacetylene. The effect of electron correlation on the structure of finite polyenes is analyzed in detail. The MP3/6–31G* C(DOUBLE BOND)C and C(SINGLE BOND)C bond lengths in polyacetylene are estimated by a simple extrapolation method using empirical corrections for the MP2 deficiencies, yielding values [C(DOUBLE BOND)C(MP3) ∼ 1.36 Å and C(SINGLE BOND)C(MP3) ∼ 1.44 Å] that are in a good agreement with experiment (C(DOUBLE BOND)C (DOUBLE BOND) 1.36 Å and C(SINGLE BOND)C (DOUBLE BOND) 1.44–1.45 Å). Comparison is also made with other theoretical estimates of polyacetylene structure. E_dim is approximated by the energy difference between the equilibrium and hypothetical polyenic structures. It is estimated that E_dim is ∼ 1.4–1.5 kcal/mol (0.06–0.07 eV) per carbon-carbon bond at the HF level with 4–21G and 6–31G* basis sets and ∼ 0.3–0.5 kcal/mol (0.013–0.022 eV) at the MP2 level with the 6–31G* basis set. It is concluded that E_dim is very sensitive to the level of approximation employed so that a proper treatment of electron correlation is essential to obtain a reliable estimate of the dimerization energy. © 1997 John Wiley & Sons, Inc.     

Theoretical study of intramolecular hydrogen bonding and molecular geometry of 2-trifluoromethylphenol

The conformational behavior of 2-trifluoromethylphenol was investigated by means of theoretical calculations. Four characteristic structures have been found on the potential energy hypersurface of the compound: anti form (local minimum), in which the hydroxy hydrogen points away from the trifluoromethyl group; and three syn forms (the hydrogen points towards the trifluoromethyl group), with different trifluoromethyl torsions (global minimum, one low and another one high lying saddle-point). The geometry of these conformers were optimized by ab initio calculations using 6-31G** basis set. The effects of electron correlation were investigated by MP2 and various DFT methods. To investigate the intramolecular interaction in the syn forms, the electron density distribution was calculated at the MP2 level of theory. In the structure corresponding to the global minimum at the MP2/6-31G** level a bond critical point was found in Bader's sense between the hydroxy hydrogen and a fluorine of the trifluoromethyl group indicating hydrogen bonding interaction. The length of the hydrogen bond, 1.98 Å, corresponds to medium strength interaction. The O(SINGLE BOND)H bond is slightly twisted and the C(SINGLE BOND)F bond, interacting with it, is considerably twisted out of the plane of the benzene ring to the same side of the ring. The most pronounced geometrical consequence of the hydrogen bond is the 0.02-Å lengthening of the C(SINGLE BOND)F bond participating in its formation. All the other geometrical changes in 2-trifluoromethylphenol, as compared with trifluoromethylbenzene and phenol, are also consistent with the phenomenon of resonance-assisted hydrogen bonding. © 1996 by John Wiley & Sons, Inc.     

Synthesis and crystal structure of 2-{5-[2-(2,6-dichlorophenylamino)benzyl]-4-p-tolyl-4H-1,2,4-triazol-3-ylthio}acetate

The compound 2-{5-[2-(2,6-dichlorophenylamino)benzyl]-4-p-tolyl-4H-1,2,4-triazol-3-ylthio}acetate has been prepared and characterized by IR, ¹H NMR, ¹³C NMR and mass spectra. The crystal and molecular structure were further confirmed using single crystal X-ray diffraction. The crystal structure has been found to be stabilized by intermolecular C–H···O interaction generating bifurcated hydrogen bonds whereas the C–H···N interactions generate chain of molecules. The intramolecular N–H···N hydrogen bond forms a ring with S(7) graph-set motif.     

A comparative study of O2, CO,and NO binding to iron–porphyrin

Minimum-energy structures of O₂, CO, and NO iron–porphyrin (FeP) complexes, computed with the Car–Parrinello molecular dynamics, agree well with the available experimental data for synthetic heme models. The diatomic molecule induces a 0.3–0.4 Å displacement of the Fe atom out of the porphyrin nitrogen (N_p) plane and a doming of the overall porphyrin ring. The energy of the iron–diatomic bond increases in the order Fe(SINGLE BOND)O₂ (9 kcal/mol) < Fe(SINGLE BOND)CO (26 kcal/mol) < Fe(SINGLE BOND)NO (35 kcal/mol). The presence of an imidazole axial ligand increases the strength of the Fe(SINGLE BOND)O₂ and Fe(SINGLE BOND)CO bonds (15 and 35 kcal/mol, respectively), with few structural changes with respect to the FeP(CO) and FeP(O₂) complexes. In contrast, the imidazole ligand does not affect the energy of the Fe(SINGLE BOND)NO bond, but induces significant structural changes with respect to the FeP(NO) complex. Similar variations in the iron–imidazole bond with respect to the addition of CO, O₂, and NO are also discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 31–35, 1998     

C—H···X (X = N,O, S) intramolecular interaction in 1‐vinyl‐2‐(2′‐heteroaryl)pyrroles as monitored by 1H and 13C NMR spectroscopy

¹H and ¹³C NMR spectroscopy of a series of 1‐vinyl‐2‐(2′‐heteroaryl)‐pyrroles were employed for the analysis of their electronic and spatial structure. The C—H···N intramolecular interaction between the α‐hydrogen of the vinyl group and the pyridine nitrogen, a kind of hydrogen bonding, was detected in 1‐vinyl‐2‐(2′‐pyridyl)pyrrole, which disappeared in its iodide methyl derivative. It was shown that this interaction is stronger than the C—H···O and C—H···S interactions in 1‐vinyl‐2‐(2′‐furyl)‐ and ‐2‐(2′‐thienyl)‐pyrroles. Copyright © 2001 John Wiley & Sons, Ltd.     

Chain transfer by addition-fragmentation mechanism. VII. Radical polymerization of vinyl monomers in the presence of ethyl 2-[1-(trimethylsilylperoxy)ethyl]propenoate and related compounds

Ethyl 2-[1-(trimethylsilylperoxy)ethyl]propenoate 1 , ethyl 2-[1-(dimethylvinylsilylperoxy)-ethyl]propenoate 2 , ethyl 2-[1-(1-(2-ethoxycarbonyl-1-methyl-2-propenylperoxysilyl)-1-methylethylperoxy)ethyl]propenoate 3 , and 2-phenyl-2-trimethylsilylperoxypropane 4 were synthesized and added to the free radical polymerization of vinylic monomers. 1 and 2 were found to show no homopolymerizability but act as effective chain transfer reagents in radical polymerizations of methyl methacrylate (MMA), styrene (St), and n-butyl acrylate (BA). The estimated chain transfer constants (C_tr) are as follows: C_tr ( 1 ) = 0.15 for MMA, 0.90 for St, and 2.03 for BA at 60°C; C_tr ( 2 ) = 0.12 for MMA, 1.16 for St, and 1.9 for BA at 60°C. ¹H–NMR spectra of poly(St) formed in the presence of 1 is consistent with the view that the polymers bear an oxirane at one terminal and an trimethylsilyloxy fragment at the other end. Moreover, peroxysilane 4 showed very low transfer properties by direct homolytic substitution (SH₂). These findings indicate that the ethyl 2-[1-(substituted dimethylsilylperoxy)ethyl]-propenoates 1–3 undergo chain transfer reaction via a intramolecular homolytic substitution (SHi) following an addition process. Preparation of poly(styrene) up to high conversion in the presence of 3 yielded to the formation of the corresponding polymeric structures bearing hydrolysable C(SINGLE BOND)O(SINGLE BOND)Si(SINGLE BOND)O(SINGLE BOND)C bonds. © 1996 John Wiley & Sons, Inc.     

Two-dimensional sheet based on C–H···N hydrogen bonds within an organic cocrystal: a crystallographic,spectroscopic and theoretical study

The cocrystal containing 1,2,4,5-tetracyanobenzene (TCNB) and trans-1,2-bis(4-pyridyl)ethylene (4,4′-BPE) has been realised (TCNB)·(4,4′-BPE) 1. Compound 1 produces a two-dimensional sheet based on two different types of C–H···N hydrogen bonds. Each molecule within the cocrystal functions as both a donor and an acceptor of hydrogen bonds. Weak hydrogen bonds such as these, acting as the driving force to produce a polymeric assembly, are not investigated as frequently as stronger and more traditional O–H···O and O–H···N hydrogen bonds within multicomponent cocrystals. The existence of the different types of C–H···N hydrogen bonds was confirmed by single-crystal X-ray diffraction as well as infrared spectroscopy. The overall interaction energies for both types of hydrogen bonds were determined by computational calculations at various levels of theory.     

Polysulfonylamine. CLIV [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 7 [2] Ein dreidimensionales Koordinationspolymer aus Schichten und Pfeilern: Kristallstruktur von Ba[(CH3SO2)2N]2·2H2O

Polysulfonylamines. CLIV. Crystal Structures of Metal Di(methanesulfonyl)amides. 7. A Three‐Dimensional Coordination Polymer Built up from Layers and Pillars: Crystal Structure of Ba[(CH₃SO₂)₂N]₂·2H₂O The barium compound BaA₂·2H₂O, derived from HA = di(methanesulfonyl)amine, has been characterized by single crystal X‐ray diffraction at —95 °C (monoclinic, space group P2₁/n, Z = 4). Despite numerous metal‐ligand bonds, the independent anions A^— and A′^— retain the pseudo‐C₂ symmetric conformation that commonly occurs in organic onium salts BH⁺A^—. The large cation attains ninefold coordination via interactions with one (O, N)‐chelating A^—, three κ¹O‐bonding A^—, two κ¹O‐bonding A′^— and two monodentate water molecules; if a distinctly longer barium‐water distance is included, the coordination number may alternatively be viewed as 9 + 1 and one water molecule regarded as an asymmetrically μ₂‐bridging ligand. In contrast to the previously reported layer structures of SrA₂ and PbA₂, the present crystal displays a three‐dimensional coordination assembly consisting of layers formed by the cations, the water molecules and the pentadentate A^— ligands, and of interlayer pillars provided by the bidentate A′^— ligands; however, the Ba²⁺/A^— substructure turns out to be topologically and crystallographically congruent with the corresponding M²⁺/A^— substructures in SrA₂ and PbA₂. The crystal cohesion of the barium complex is reinforced by four O(W)—H···O=S hydrogen bonds and several non‐classical C—H···O=S hydrogen bonds.