Alkoxy Oxygen Research Articles

The effects of the bulkiness of terminal chains on the stability of smectics deduced from the crystal structures of isomeric chiral biphenyl esters

Single crystal X-ray analyses have been performed on 4'-octyloxyphenyl 4'-[(S)1-methylheptyloxy]biphenyl-4-carboxylate (8*O-O8) and 4-[(S)-1-methylheptyloxy]phenyl 4'-octyloxybipheny-4-carboxylate (8O-O8*), with the phase sequences Cr-SmC*-Ch-I and Cr-SmX-SmC*-SmA-I, respectively. Both crystals have smectic-like layer structures, in which the molecular tilt angles are 10 and 30, respectively. In the crystal phase of 8*O-O8, biphenyl moieties are twisted probably because of steric hindrance of the bulky chiral chains linked to them, whereas in 8O-O8* they are nearly planar due to the conjugation between the alkoxy oxygen atoms and the carbonyl groups. From comparison of the properties with those of other related compounds, it is concluded that the conformation of the biphenyl moieties are closely related to the stability of smectic phases.

Oxovanadium alkoxide complexes. Syntheses and crystal structures of (Ph 4P) 2[(VO) 2Cl 4(OR) 2] (R = −CH 3, −CH 2CH 2Cl) and [(VO) 2Cl 2MeC(CH 2OH) (CH 2O) 22

The reactions of (Ph 4P) [VO 2Cl 2] in various alcohols yield complexes of the type (Ph 4P) 2[(VO) 2Cl 4(OR) 2] (R=−CH 3( 1), −CH 2CH 2Cl ( 2)). Similarly, the reaction of (BzPh 3P) [VO 2Cl 2] with tris(hydroxymethyl)ethane yields [(VO) 2Cl 2MeC(CH 2OH)(CH 2O) 2 2]∗d2BxPh 3PCl∗d2CH 3OH ( 3∗d2BzPh 3PCl∗d2CH 3OH). The molecular anions of complexes 1 and 2 consist of binuclear units of edge-sharing V(IV) square pyramids. The alkoxy groups bridge the two V(V) sites and the ∗ V=O∗ groups adopt the anti-orientation with respect to the V 2O 2 rhombus of the bridging unit. In contrast, the neutral [(VO) 2Cl 2MeC(CH 2OH)(CH 2O) 2 2] consists of the edge-sharing V(V) octahedra. The tridentate ligands each provide one alkoxy oxygen adopting a bridging mode between V(V) sites, an alkoxy oxygen as a terminal ligand to one V(V) site and an alcohol oxygen donor as a terminal ligand to the other V(V) site. The terminal oxo-groups occupy positions approximately coplanar to the V 2O 2 rhombus of the bridging unit. Crystal data: (Ph 4P) 2[(VO) 2Cl 4(OCH 3) 2]∗d2CH 3OH ( 1∗d2CH 3OH), monoclinic P2 1/n, a = 12.068(2), b = 16.388(3), c = 12.893(3) A ̊ , β = 100.72(2)°, Z =2 . (Ph 4P) 2[(VO) 2Cl 4-(OCH 2CH 2Cl) 2] ( 2), triclinic P l, a = 11.227(2), b = 12.496(2), c = 10.609(2) A ̊ , α = 109.78(2), β = 114.68(3), γ = 85.46(3)°, Z = 1 . [(VO) 2Cl 2MeC(CH 2OH)(CH 2O) 2 2]∗d2BzPh 3PCl∗d2CH 3OH ( 3∗d2BzPh 3PCl∗d2CH 3OH), triclinic P 1, a = 10.361(2), b = 15.762(3), c = 10.125(2) A ̊ , α = 105.72(3), β = 90.02(3), γ = 79.86(3)°, Z = 1 .

Reaction of α-Peroxy Lactones with C, N, P, and S Nucleophiles: Adduct Formation and Nucleophile Oxidation by Nucleophilic Attack at and Biphilic Insertion into the Peroxide Bond

The reactions of the α-peroxy lactones 1 with a variety of carbon, nitrogen, phosphorus, and sulfur nucleophiles yield, on SN2 attack at the more electrophilic alkoxy oxygen of the peroxide bond, diverse addition and oxygen transfer products, together with the catalytic Grob-type fragmentation. The nature of the nucleophile determines the fate of the open-chain intermediate I. Thus, protic nucleophiles such as primary and secondary amines and thiols lead to the second intermediate I‘ through proton shift subsequent to the SN2 step, while nonprotic amines and sulfides, as well as diazoalkanes, lead to oxidation products or to the cycloadducts 10−15. Trivalent phosphorus nucleophiles such as phosphines and phosphites and diisopropyl sulfoxylate prefer biphilic insertion, as documented by the fact that the nucleophilicity rather than the steric demand of these reagents controls their reactivity. The labile adducts undergo a variety of transformations to the final stable products. For protic nucleophiles, the...

1,5-Ph3Ge and 1,6-Bu3Sn Group Transfer from Enoxy Oxygen to Alkoxy Oxygen

Abstract 1,5-Ph3Ge and 1,6-Bu3Sn group transfer from enoxy oxygen to alkoxy oxygen are observed in radical reaction of keto epoxides and keto oxetanes, respectively.

Coordination Behavior of ω-(Trichlorostannyl)alkyl Acetates, CH3COO(CH2)nSnCl3 (n = 3−5): A Solution and Solid-State Multinuclear NMR and AM1 Quantum-Chemical Study

The coordination behavior of three ester-functionalized monoorganotin trichlorides of the type ω-(trichlorostannyl)alkyl acetate, CH3COO(CH2)nSnCl3 (n = 3−5), has been investigated by multinuclear solid- and solution-state NMR, as well as AM1 quantum-chemical calculations. The data reveal basically the existence of a fast equilibrium between two species involved respectively in an intramolecular and intermolecular donor-acceptor interaction between the ester function and the tin atom. In the n = 3 case, the species involving the intramolecular interaction is by far the dominant one, with a coordination from the alkoxy oxygen atom to the tin atom, resulting in an interaction of the type −CH2O(Ac)→SnCl3 (Ac = CH3CO−). In contrast, for the n = 4 and 5 cases, the species involving the intermolecular interaction prevails, resulting in (cyclo)dimeric or oligomeric species displaying coordinations from the carbonyl oxygen atom to the tin atom of the type −CH2OC(CH3)O→SnCl3.

X-ray Diffraction and Gradient-Assisted 2D 1H−119Sn HMQC NMR Studies on the Structure of Condensation Complexes of Salicylaldoxime and Dimethyltin(IV) Oxide

Reaction of dimethyltin(IV) oxide with salicylaldoxime in the molar ratio 3:2 or 1:1 in refluxing toluene/ethanol (4/1) affords reaction mixtures which, upon crystallization from alcohols TOH (T = Me, Et, n-Pr, i-Pr), generate compounds with three dimethyltin and two salicylaldoximate moieties. These compounds obey the formula [(Me(2)Sn)(Me(2)SnO)(Me(2)-SnOT)(HONZO)(ONZO)], where HONZOH represents salicylaldoxime, o-HON=CHC6H4OH. X-ray diffraction analysis of the compounds at room temperature (T = Me, compound 3; T = Et, 4; T = n-Pr, 5; T = i-Pr, 6) reveals that all structures contain one seven-coordinate tin atom bound to two nitrogen and three oxygen atoms in the equatorial plane of a pentagonal bipyramid, the two methyl groups being in apical positions. The two other tin atoms are five-coordinate with a trigonal-bipyramidal geometry having the two methyl groups and a common oxygen atom in the equatorial positions and, in apical positions, two further oxygen atoms, of which the trifurcated alkoxy oxygen atom bridges these tin atoms. Reaction of dimethyltin(IV) oxide with salicylaldoxime in the molar ratio 1:1 in refluxing benzene generates, after solvent evaporation, compound 2b, obeying the formula [(Me(2)Sn)(2)(Me(2)SnO)-(HONZO)(ONZO)(HONZO)]. The solution-state structures of the alkoxy-bridged compounds 3-6, investigated by gradient-assisted 2D H-1-Sn-119 HMQC as well as H-1-C-13 HMQC and HMBC NMR spectroscopy, are the same as those in the solid state. The bonding mode of the third ligand (i.e. HOZNO) of compound 2b has been elucidated.

Steric and Stereoelectronic Control of the Mode Selectivity as a Function of Alkene Structure in the Reaction with Dimethyl α-Peroxy Lactone: Cycloadducts and Ene Products versus Epoxides

The oxidation of di-, tri-, and tetrasubstituted alkenes 2 by dimethyl α-peroxy lactone (1) affords the cycloaddition, ene, and epoxidation products 3−6. In the presence of methanol, additionally the trapping products 7 are obtained. The observed dichotomy in the product distribution requires two different paths for this reaction, namely a path via an open, stretched 1,6 dipole and another path for epoxidation. Both paths arise from an SN2 attack of the double bond of the alkene 2 on the peroxide bond of the α-peroxy lactone 1, the first unsymmetrical (end-on attack), leading to the 1,6 dipole A, and the second symmetrical (central attack) with respect to the approach of the double bond, leading to epoxidation. The 1,6 dipole is postulated to afford the cycloadducts, of which the thermodynamically favored diastereomers are obtained, and the ene products. In the epoxidation, the α-lactone released after oxygen transfer oligomerizes to the polyester 8 or in the presence of methanol is trapped as α-methoxy acid 9. The reaction is regioselective both with respect to the attacked oxygen atom of the α-peroxy lactone 1, as revealed by the trapping products 7, as well as with respect to the attacking carbon atom for unsymmetrical alkenes 2c,d, as displayed by the ene products 5 and 6. The former regioselectivity is dictated by the inherent polarization of the peroxide bond through the carbonyl group which makes the alkoxy oxygen the more electrophilic one toward nucleophilic attack, while for the latter the incipient positive charge of the open 1,6 dipole is better stabilized by the more substituted carbon atom of the end-on attacking unsymmetrical alkene. The preferred reaction mode has been found to be sensitive to the structure of the alkene and the difference in reactivity has been explained in terms of steric and stereoelectronic factors. Thus, for the sterically less hindered cis-di- and trisubstitued alkenes the path along the open 1,6 dipole is favored (stereoelectronic control), while the more sterically demanding trans-di- and tetrasubstituted alkenes react by the epoxidation mode (steric control).

Structure-reactivity relationships for beta-galactosidase (Escherichia coli, lac Z). 1. Brønsted parameters for cleavage of alkyl beta-D-galactopyranosides.

Seven substituted alkyl beta-D-galactopyranosides 1-OR have been prepared and shown to be fair to excellent substrates for hydrolysis catalyzed by beta-galactosidase (Escherichia coli, lac Z). Brønsted parameters of (beta 1g)k3 = -0.49 +/- 0.13 and (beta 1g)kcat/Km = -0.75 +/- 0.14, respectively, were determined at pH 8.6 for k3 (s-1), the first-order rate constant for cleavage of enzyme-bound 1-OR, and kcat/Km (M-1 s-1), the second-order rate constant for reaction of the free enzyme and 1-OR. There is a weak correlation between log Km and the pKa of the alkyl alcohol leaving group, which is attributed to stabilization of the Michaelis complex by hydrophobic interactions between the enzyme and electron-withdrawing halogen substituents at the alkoxy leaving group. These binding interactions are probably both productive and expressed in the value of kcat/Km and nonproductive and expressed in the value of k3. The negative values of beta 1g are inconsistent with enzymatic catalysis of endocyclic cleavage of the glycosidic bond. The values of beta 1g for enzyme-catalyzed cleavage of alkyl beta-D-galactopyranosides lie between those observed for the spontaneous (beta 1g approximately -1.25) and specific-acid-catalyzed (beta 1g approximately 0) cleavage of acetals, and these pathways are therefore excluded for the enzyme-catalyzed reaction. Removal of the metal cofactor Mg2+ from the enzyme causes a approximately 0.2 unit decrease in (beta 1g)k3 for beta-galactosidase-catalyzed cleavage of 1-OR. The interpretation of this change in beta 1g is unclear. The Brønsted coefficients for the beta-galactosidase-catalyzed reaction are consistent with participation by an essential catalytic residue in concerted general-acid catalysis of cleavage of the glycosidic bond of 1-OR and/or stabilization of developing negative charge at the alkoxy oxygen by interaction with the magnesium ion cofactor.

β‐Alkoxy‐ and β‐Hydroxyalkylphosphanes as Ligands in the Stereoselective Hydrogenation — A Comparison

Optically pure 1,4-bis(diphenylphosphanyl)-2-hydroxy-butane (2) and its methyl ether 1 can be conveniently prepared by starting from chiral pool substances such as malic or L-ascorbic acid. Different pathways to these compounds were elucidated. In one case an interesting migration of an acetalic OH-protective group was observed. The reaction of the bisphosphanes with Rh1 or PdII gave uniform metal complexes. On the basis of X-ray structural analysis, NMR and IR data it was concluded that in the investigated precatalysts of the type [Rh(COD)(bisphosphane)]BF4 a coordination of the alkoxy or hydroxy oxygen to the metal does not take place. Nevertheless, significant differences in enantioselectivity and activity could be observed when several prochiral substrates were hydrogenated.

Topochemical Photopolymerization of 4-[2-(Unsubstituted and Methyl-Substituted Pyrazinyl)ethenyl]cinnamates and -thiocinnamates in the Crystalline State

Abstract Topochemical photopolymerization of 4-[2-(unsubstituted and methyl-substituted pyrazinyl)ethenyl]cinnamates and -thiocinnamates were carried out in the crystalline state. Upon photoirradiation, ethyl 4-[2-(unsubstituted and methyl-substituted pyrazinyl)ethenyl]cinnamates and S-ethyl 4-[2-(unsubstituted and methyl-substituted pyrazinyl)ethenyl]thiocinnamates gave α-hetero-type crystalline linear polymers, whereas methyl 4-[2-(methyl-substituted pyrazinyl)ethenyl]cinnamates afforded mixtures of β-type oligomers. The X-ray crystallographic analyses of the monomers revealed that the thioesters were more favorable monomers than the corresponding esters from the viewpoint of close packing in a crystal. The following factor(s) would play an important role in determining their molecular arrangements: 1) The close contact between the central 1,4-phenylene ring and the alkoxy oxygen of the ester group or the alkylthio sulfur of the thioester group, 2) the hydrogen bond between the interstacked pyrazinyl groups, and/or 3) the gearing of the alkyl group in the ester moiety with the methylpyrazinyl group.

Matrix-Isolation Infrared Spectroscopy of Hydrogen-Bonded Complexes of Triethyl Phosphate with H2O, D2O, and Methanol

The infrared spectra of adducts of triethyl phosphate (TEP) with H2O, D2O, and methanol (MeOH), isolated in a nitrogen matrix, are reported. A red shift in the phosphoryl (P=O) stretching vibration of triethyl phosphate was seen, which indicated adduct formation. Adducts of the type 1:1 and 1:2 of TEP…H2O and TEP…MeOH were identified in the matrix. It was observed that adduct formation occurred only with the phosphoryl oxygen and not with the alkoxy oxygen of triethyl phosphate. A red shift in the OH stretching vibration of water, as well as that of methanol, was also observed because of adduct formation. Solution spectra of TEP were also recorded in the same solvents and compared with the matrix spectra.

Homolytic 1,5-transfer of organosilicon groups from an enoxy oxygen to an alkoxy oxygen

The homolytic 1,5-transfer of both trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) groups from an enoxy oxygen to an alkoxy oxygen has been observed for the first time.

On the mechanism of hydrolysis of sulfinate esters: oxygen isotope exchange and theoretical studies

A small but detectable amount of 18O loss at the sulfinyl oxygen was observed during acid hydrolysis of 18O-labelled methyl benzenesulfinate, while no detectable loss of the label was found during alkaline hydrolysis. The relative rates of the acid-catalysed isotope exchange and hydrolysis were evaluated to be about 1/200. This large difference in the rates seems to be incompatible with the reaction of water with the conjugate acid of the substrate protonated at the sulfinyl oxygen. A mechanism involving an SN2-like reaction at the sulfur through the protonation at the alkoxy oxygen of the substrate is proposed on the basis of theoretical calculations.

ChemInform Abstract: Alkoxy and Cyclic Ether Oxygens Exhibit Disparate Capabilities for Directing ortho‐Lithiation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Trispyrazolylborate degradation and the crystal structure of [Mo(NO)(CO) 2{HB(OPr i)(3-Pr i-5-MeC 3HN 2) 2}

The complex [Mo(NO){HB(OPr i(3-Pr i-5-MeC 3HN 2) 2}(CO) 2] has been isolated from one attempt to prepare [Mo(NO){HB(3-Pr i-5-MeC 3HN 2) 3}(CO) 2]; a crystal structure shows the presence of an isopropoxide group with the alkoxy oxygen bound to the boron and molybdenum atoms [Mo—O = 2.225(5) Å].

Alkoxy and cyclic ether oxygens exhibit disparate capabilities for directing ortho lithiation

Metalation of 4a and 4b with n-butyllithium under kinetically controlled conditions (C 6H 6, 20 °C or Et 2O, TMEDA (2 equiv), 20 °C) leads to preferred deprotonation α to the heterocyclic ring.

FT-IR spectroscopic studies of polyurethanes: Part 3. Quantum chemical studies of the carbamate group and the urethane C-O-C hydrogen bonding in polyurethanes

Ab initio quantum chemical computations were carried out on (a) methyl carbamate, (b) N-methyl methyl carbamate, and (c) the N-methyl methyl carbamate dimers: (i) to determine the optimized parameters, the relative strengths of cis versus trans conformations, and the dipole moment of the carbamate group; (ii) to determine the optimized bond parameters of the N-methyl methyl carbamate (a model for the urethane C-O-C group) and the relative energies of the cis and trans conformations; (iii) to determine the relative strengths of the C-O-C and CO H-bonds. The basis set used was the 3-21G set of the gaussian 80 program obtained from QCPE, Bloomington, IN. Variations in the strengths of these two H-bonds with the Nctdot;O distance (where O is either the carbonyl or the urethane alkoxy oxygen atom) were studied and found to be similar in behavior. The cis carbamate group was found to be energetically more stable than the trans one by 10.74 kcal mol −1. The strength of the urethane C-O-C H-bond was computed to be 5.95 kcal mol −1, which is quite significant compared to the value of 8.25 kcal mol −1 for the more accepted “carbonyl” H-bond. The urethane C-O-C H-bond is found to be directional, specific and non-negligible. Computed dipole moments are in very good agreement with experimental results. Work with two more basis sets has indicated that the results so obtained are not dependent on the choice of the basis set.

Homolytic 1,6-transfer of the Bu3Sn group from allylic carbon to alkoxy oxygen

A novel 1,6-Bu3Sn group transfer from allylic carbon to alkoxy oxygen is observed in radical reactions of vinyl oxetanes; it is greatly favoured over 1,5- and 1,6-hydrogen atom transfer.

Trinuclear polyoxomolybdates, the crystal and molecular structure of [(n-C 4H 9) 4N][Mo 3O 6(OCH 2CH 2Cl){(OCH 2) 3CCH 3} 2

The reaction of [(n-C 4H 9) 4N] 4[Mo 8O 26] with 2-(hydroxymethyl)-2-methyl-l,3-propanediol (H3hmmp) in acetonitrile yields (TBA) 2[Mo 3O 7(hmmp) 2] ( 1). Complex 1 reacts with chloroacetic acid and alkylating agents to yield the derivatives (TBA)[Mo 3O 6(OH)(hmmp) 2] ( 2) and (TBA)[Mo 3O 6(OR)(hmmp) 2] ( 3), respectively. The direct reaction of (TBA) 4[Mo 8O 26] with H 3hmmp in chloroethanol yields (TBA)[Mo 3O 6(OCH 2CH 2Cl)(hmmp) 2 ( 4). The structure of 4 consists of discrete trinuclear anions [Mo 3O 6(OCH 2CH 2Cl)(hmmp) 2] - and TBA + cations. Two of the molybdenum centers exhibit similar coordination environments, each bonding to two terminal oxo groups, one terminal hmmp alkoxy donor and three bridging alkoxy, oxygens from the hmmp ligands. The third molybdenum center coordinates to two terminal oxo groups, a terminal chloroethanolate ligand, and three bridging alkoxy oxygens of the hmmp ligands. Crystal data: monoclinic space group P2 1/ n, a=12.224(2), b=23.178(3), c=13.562(3) Å, β= 97.05(1)°, V=3813.1(11) Å 3, Z=4. Structure solution and refinement based on 4794 reflections (Mo Kα, λ=0.71073 Å, 2θ⩽45°) converged at a conventional discrepancy value of 0.052.

Theoretical studies on the acid hydrolysis of methyl carbamate

AbstractThe mechanism of the A2 acid hydrolysis of methyl carbamate was investigated using MNDO method. The reaction was found to proceed in two steps: (1) the rate‐determining nucleophilic attack of water on the carbonyl carbon of the N‐protonated tautomer involving the tetrahedral TS; and (2) the fast subsequent proton abstraction by the leaving group, NH3, to form products. The mechanism is similar to that involved in the A2 hydrolysis of acetamide. Effects of substituents, R1, R2, and R3 in R1OCONR2R3, on rates can be predicted by the changes in electron densities on alkoxy oxygen and N, in complete agreement with the experimental results. We concluded that there is no need for invoking two different mechanisms for amides and carbamates since a common mechanism can easily accommodate all the experimental results.