Influence Of Steric Effects Research Articles

Study of photochemical addition of acyl radical to electron-deficient olefins

The photochemical addition of acyl radical to electron-deficient olefins is studied. The scope of the reaction, the mechanism, the role that molecular oxygen plays, the influence of steric effects, and the side reaction that take place are discussed. The reaction was carried out using a range of electron-withdrawing substituents (ketones, amides, lactones, nitrile and esters) with good yields of the corresponding photoadduct in all cases.

Crystal structure oftrans-ethyl(1,5,6-trimethylbenzimidazole)-bis(dimethylglyoximato)cobalt(III). Relationships between structural and spectroscopic properties in compounds of the general formulae [Co(dmgH)2(R)(1,5,6-Me3Bzm)

The synthesis and x-ray crystal structure oftrans-[Co(dmgH)2(Et)(1,5,6-Me3Bzm)] where dmgH=dimethylglyoximate(−1), and 1,5,6-Me3Bzm=1,5,6-trimethylbenzimidazole, is reported. The compound C19H26N6O4Co is monoclinic, space group P21/n;a=11.700(4);b=24.205(6);c=8.500(3) A and β=101.63(3)°. D(calcd) 1.299 g cm−3; Z=4 and R=0.066 for 2359 independent reflections. Comparison of Co-N(axial ligand) bond lengths for compounds of general formulaetrans-[Co(dmgH)2(R)(L)], with L=pyridine or 1,5,6-trimethylbenzimidazole and R=CH(CN)Cl, CH2NO2, Me, Et,i-Pr, cyclo-hexyl or adamantyl is made. The Co−N(1,5,6-Me3Bzm) bond lengths of the trimethylbenzimidazole derivatives show a fairly linear relationship with the electronic parameter of the axial R group, derived from the13C-n.m.r. spectra of their pyridine analogues. The influence of steric effects on the properties of these CoIII compounds is discussed.

The influence of steric effects in substituted 2,2′-bipyridine on the spin state of iron(II) in [FeN 6] 2+ systems

Tris(ligand)iron(II) complexes of 6-methyl-2,2′- bipyridine (mbpy) and 2-(pyridin-2-yl)quinoline (pyq) display anomalous magnetic properties which are associated with a temperature-induced singlet ( 1A 1) ⇋ quintet ( 5T 2) transition. Two forms of [Fe(pyq) 3][ClO 4] 2 were obtained: one which is essentially high spin over the range 89–300 K and the other which shows an almost complete, gradual transition in this range. In the three complex salts of [Fe(mbpy) 3] 2+ isolated, the perchlorate, fluoroborate and hexafluorophosphate, appreciable spin- pairing is observed at low temperatures but in no instance is the transition to singlet state species complete at 89 K. Data for solutions of both [Fe (mbpy) 3] [ClO 4] 2 and [Fe(pyq) 3] [BF 4] 2 indicate that negligible spin-pairing is observed down to 210 K. Mössbauer spectral data confirm the change in spin state populations in all solid salts and moreover indicate two sites for the high-spin species at low temperatures. It is believed that these may arise from ordering of anion sites in the lattice. In the room temperature structure of [Fe(mbpy) 3] [ClO 4] 2· 1 2 mbpy disorder of one of the anions as well as the occluded free ligand occurs. In the structure of the complex cation considerable distortion is observed with the average FeN distance being 2.21 Å. The ligand molecules are not planar, the pyridyl rings being twisted 4.3, 16.4 and 17.8° about the inter- ligand bridge. The methyl substituent induces a steric barrier to coordination and also greater inter-ligand repulsions than in complexes of bpy and this is presumably responsible for the accessibility of the quintet state for Fe(II). The steric effects of the fused benzene ring in pyq are predicted to be similar. [Fe(mbpy) 3] [ClO 4] 2· 1 2 mbpy crystallises in space group P2 1/ c ( Z = 4) with cell parameters a = 19.769(10), b = 13.186(4), c = 15.043(8) Å. A total of 2509 reflections with I o > 3σ( I o) were observed and gave a final R = 0.057.

The reactions of NO3 with OH and H

Rate constants for the reaction NO3+ OH → products (1) have been measured in a flow system. NO3 radicals were generated from the reaction of F with HNO3, and OH radicals were generated by the reaction of H with NO2. Concentrations of NO3 were determined by multipass optical absorption in the visible region, while [OH] was measured by resonance fluorescence. Numerical modelling allowed a rate coefficient to be derived for the reaction at room temperature of k1=(2.0 ± 0.6)× 10–11 cm3 molecule–1 s–1. The modelling shows that secondary reactions are of only minor importance.We describe a hitherto-unknown reaction between H and NO3. NO3+ H → OH + NO2. (2) Production of OH was demonstrated explicitly from the resonance fluorescence measurements. The reaction is fast, with a room-temperature rate constant given by k2=(1.1 ± 0.6)× 10–10 cm3 molecule–1 s–1. Reaction (1) follows the formation of OH in reaction (2), so that the time-dependence of [OH] can be used to give further information about k1. The rate constants so obtained were entirely consistent with those obtained in the direct study.The possible influence of steric effects and orbital degeneracy on the relative rates of the H and OH interactions with NO3 are pointed out. Atmospheric involvement of the reactions, in either troposphere or stratosphere, is shown to be improbable, although the new data illustrate that NO3 can be highly reactive towards suitable partners.

Vinylic organoboranes. 4. A general, one-pot synthesis of 6- and 7-alkyn-1-ols via boracyclanes. Influence of steric effects in the iodination of lithium alkynyl ate complexes of dialkylborinates

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVinylic organoboranes. 4. A general, one-pot synthesis of 6- and 7-alkyn-1-ols via boracyclanes. Influence of steric effects in the iodination of lithium alkynyl ate complexes of dialkylborinatesHerbert C. Brown, D. Basavaiah, and N. G. BhatCite this: J. Org. Chem. 1986, 51, 24, 4518–4521Publication Date (Print):November 1, 1986Publication History Published online1 May 2002Published inissue 1 November 1986https://doi.org/10.1021/jo00374a005RIGHTS & PERMISSIONSArticle Views365Altmetric-Citations21LEARN 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 (479 KB) Get e-Alerts Get e-Alerts

Beiträge zur chemie des bors: CLXXV. Über den einfluss sterischer faktoren auf die konformation von diborylaminen

The aminoborane Ph 2BN(CMe 3SiMe 3 possesses a relatively long BN bond (1.433 Å) and a nonplanar C 2BNCSi (τ(C 2B/NCSi) 45°) skeleton as shown by X-ray structure analysis. In addition, the structure of five diborylamines have been determined by X-ray methods. The compounds (mes 2B) 2NH and (mes 2BNH) 3B belong to diborylamines with a coplanar conformation for the C 2BNHBC 2 (or C 2BNHBN 2) units, while the diborylamines (Ph 2B) 2)NH and (Ph 2B) 2NMe adopt a twist conformation. Finally, an orthogonal conformation was detected for t-Bu 2BNMe-9-borafluorene. The T-Bu 2B group stands almost perpendicular on the BNC-9-borafluorene plane. Consequently, two distinctly different BN bond lengths (1.482 and 1.392 Å) are observed. The influence of steric effects on the conformation and bonding parameters is discussed.

Influence of steric effects upon the rate constants for competing BAC2 and E1cB ester hydrolyses

On compare les vitesses d'hydrolyse de cyano-2 dimethyl-3,3 butyrates d'alkyle et d'aryle avec celles des cyanoacetates correspondants

Steric Effects in the Addition of Alkyl Radicals to Alkenes

The influence of steric effects on the addition of alkyl radicals to alkenes important in polymerizations can be investigated by the method of competition kinetics. Cyclohexyl radicals add to α- and β-substituted acrylic acid esters at different rates—a confirmation of the model (1) obtained by calculations for the transition state of this type of reaction.

Reaction of dicarbonyl compounds with dimethyl 3-ketoglutarate. Influence of steric effects on success of the condensation

The influence of steric factors on the synthesis of substituted bicyclo[3.3.0]octane-3,7 diones via the condensation of 1,2-dicarbonyl compounds with dimethyl 3-ketoglutarate 2 is described.

Phosphonate complexes. Part 6. Influence of steric effects, solvation, and chelation on stability

The interaction of some phosphonic acids RPO(OH)2, chosen to introduce different controlling factors (R = But, cyclo-C6H11, Ph, n-C10H21, Me2NCMe2, CH2SEt, CH2CH2CO2–), with CaII and CuII has been investigated by potentiometry at 25 °C, I= 0.1 mol dm–3(K[NO3]). The selection of the species and the refinement of the stability constants illustrates the applicability of a new version of the program MUCOMP. Examination of linear free-energy plots indicates that factors other than polar effects are of significance, i.e. chelate formation with the potentially bidentate ligands and particularly solvation effects which preferentially stabilize the complexes of α-branched-chain phosphonates. Other features (steric hindrance, predominance of some microscopic forms) are discussed.

13C NMR of polycyclic aromatic compounds. A review

AbstractThe analysis of the 13C NMR spectra of polycyclic aromatics is discussed briefly. Basic trends of chemical shifts are mentioned, but the emphasis is placed on substituent‐induced chemical shifts (SCS). Semi‐empirical approaches and regressional analysis are treated. The factors controlling SCS are discussed and steric, mesomeric and π‐inductive effects are analysed.CH, CF, CC, CP and C, Metal coupling constants are investigated and the influence of steric effects, bond order, mesomerism and angle distortions in relation to some of these coupling constants is discussed. Relaxation times are described in a series of compounds. The effects of dissolved oxygen or radicals are shown and the use of T1 as a monitor of molecular tumbling is depicted. The impact of 13C NMR on the understanding of charged aromatic species, both positive and negative ions, is mentioned and new information about reaction intermediates in electrophilic aromatic substitution is outlined. The possibility of using 13C NMR to investigate charge transfer complexes is also discussed. Among other subjects treated are automerization, deuterium exchange and biosynthetic incorporation of labelled materials and, finally, quantitative analysis is briefly touched upon.

The influence of steric effects on the regio- and stereospecificity of the addition of thiolates to tert-butylacetylene in a proton-donating medium

1. A method which fully eliminates the competing free-radical reaction was developed for the nucleophilic addition of thiols to alkylacetylenes. 2. Under purely nucleophilic conditions steric effects substantially affect the regioorieatatioa of a thiolate ion adding to tert-butylacetylene. The proportion of attack at theβ atom, of the C ≡ C bond increases with increase in the volume of the nucleophilic reagent. 3. Theβ adducts are formed strictly stereospecifically by a nucleophilic mechanism, of 1,2-anti-addition, and steric effects do not affect the stereochemistry of the process. 4. It was found that the ratio of the regioisomers formed in the reaction of 1-alkynes with thiols and alcohols correlates well with Charton' s steric constants for alkyl groups in the nucleophilic reagent.

Steric effects in the reactions of αβ-unsaturated ketonep-tolylsulphonylhydrazones: a route to 1,2-benzodiazepines via 1,7-ring closure of 1,1-diaryl-3-diazoalkenes

The influence of steric effects and substituents on the reactions of the sodium salts of αβ-unsaturated ketone tosylhydrazones has been studied. The tosylhydrazone salts of acyclic αβ-unsaturated ketones and those of 2-methylenecyclohexanones underwent ready thermal 1,5-ring closure to give pyrazoles but the reactions of some 2-methylenecyclopentanone tosylhydrazones were atypical. Although 2-methylenecyclopentanone tosylhydrazone salts having a β-hydrogen atom cyclised to give 1H-pyrazoles in high yield, the ββ-dialkyl and the ββ-diaryl analogues both failed to give 3H-pyrazoles; the former decomposed by a carbenic route to give dienes and the latter underwent 1,7-ring closure to give 3H-1,2-benzodiazepines. The effect of solvent proticity on some of these reactions has been investigated, and the mechanisms of pyrazole and benzodiazepine formation are discussed. The 13C n.m.r. spectra of 3H-pyrazoles, 3H-1,2-benzodiazepines, and 1H-2,3-benzodiazepines show that ring size strongly affects the chemical shift of the saturated carbon atom attached to the azo-group.

Influence of steric effects on regio- and stereospecificity of adding thiolates to tert-butylacetylene

Influence of steric effects on regio- and stereospecificity of adding thiolates to tert-butylacetylene

Influence of Steric Effects upon Redox Potentials of Cyanine Dyes

not Available.

Influence of Steric Effects and Compressibility on Nonlinear Response to Laser Pulses and the Diameters of Self-Trapped Filaments

Steric effects and compressibility appear to be important in determining the effective Kerr constant of liquids for short laser pulses, and also the saturation of the Kerr constant. Their influence may explain the relatively high threshold power and large diameters of self-trapped light filaments which are observed in many liquids.

Influence of steric effects on direction of addition of alcohols to alkylacetylenes

Influence of steric effects on direction of addition of alcohols to alkylacetylenes

Influence of steric effects on nonlinear responses to laser pulses and the diameters of self-trapped filaments

Influence of steric effects on nonlinear responses to laser pulses and the diameters of self-trapped filaments

Imidazole derivatives containing potentially labile groupings attached to N1

A number of 1-aralkylbenzimidazoles, the amination of which with sodium amide gives 1-aralkyl-2-aminobenzimidazoles, were obtained by the reaction of substituted benzyl chlorides or benzhydryl chlorides with benzimidazole or its silver salt. The successful amination of 1-benzhydrylbenzimidazole attests to the insignificant influence of steric effects on the Chichibabin reaction in the benzimidazole series [2]. 1-Methoxymethyl-2-aminobenzimidazole was obtained by the reaction of methoxymethyl chloride with the sodium salt of 2-aminobenzimidazole in absolute dioxane.

Reaction kinetics and tacticity of macromolecules. II. Acrylic acid copolymers

AbstractThe influence of steric effects and of the microtacticity of polymeric chains has been examined during the hydrolysis of acid–ester copolymers. Four different acrylic acid–ethyl ethacrylate copolymers have been prepared; their molar acid content was 50, 67, 77, and 85%. The rate of hydrolysis was examined at different degrees of neutralization in buffered aqueous solutions at 113°C. The rate was directly proportional to the content of (acid–ester–acid) triads and was highest where the degree of neutralization was equal to 0.5. The final degree of conversion is, however, limited on account of the existence of different stereochemical structures of these (acid–ester–acid) triads. Conventional and isotactic acrylic acid–methyl acrylate copolymers have also been prepared; their molar acid content was 64.5 and 80.5% for the conventional and 67 and 80% for the isotactic copolymers. From the rates of hydrolysis measured at 103°C. in buffered aqueous solutions, it becomes evident that the isotactic polymers hydrolyze 3 to 5 times more rapidly than the conventional polymers; moreover, the final degree of conversion is much higher. Finally conventional and isotactic acrylic acid–tert‐butyl acrylate copolymers have been examined; these copolymers hydrolyze only in the presence of mineral acid; any intramolecular functional interaction is absent in both cases. This stability has been explained on the basis of a different mechanism of hydrolysis of these tertiary butyl esters.