Alkoxy Oxygen Atom Research Articles

Understanding Homolytic Translocation Chemistry—An Ab Initio Study of Some 1,5-Transfers of Silyl, Germyl and Stannyl Groups of Synthetic Significance

Ab initio molecular orbital and density functional calculations predict that 1,5-homolytic translocation reactions involving silyl, germyl and stannyl groups between two alkyl carbon atoms, between alkoxy oxygen atoms, and between alkyl and allylic carbon atoms proceed via concerted mechanisms involving frontside substitution at the higher heteroatom involved; CCSD(T)/DZP//B3LYP/DZP calculations predict energy barriers ranging from 69 to 114 kJ mol–1 depending on the system involved.

The synthesis and reactions of dialkyl fluoroalkyl phosphates

Dimethyl and diethyl fluoroalkyl phosphates were prepared from (1) a dialkyl phosphite with a fluoroalcohol, triethylamine and carbon tetrachloride, (2) a dialkyl chlorophosphate with a fluoroalcohol and triethylamine, and (3) a dialkyl chlorophosphate with the sodium salt of a fluoroalcohol. Dimethyl and diethyl (2,2,2-trifluoroethyl) phosphates reacted with bromotrimethylsilane (TMSBr) in chloroform to give two products with loss of alkyl bromide. The major product was an alkyl (trifluoroethyl) trimethylsilyl phosphate, RO(TMSO)P(O)OCH 2CF 3 and the minor product was a bis(trimethylsilyl) trifluoroethyl phosphate, (TMSO) 2P(O)OCH 2CF 3. The mechanism presumably involves initial attack of an alkoxy oxygen atom on the silicon atom of bromotrimethylsilane. Diethyl (2,2,2-trifluoroethyl) phosphate is resistant to chlorination. It did not react with oxalyl or thionyl chloride in chloroform under prolonged reflux. Unlike triethyl phosphate, it did not react with phosphorus oxychloride in chloroform under reflux.

Nitro group effects on the1J(CC) couplings in nitroalkanes

One-bond 13C–13C coupling constants across a single bond are reported for a number of nitroalkanes including cases where two or three nitro groups are attached to the same carbon atom. The nitro group effect on the 1J(CC) across the adjacent bond becomes significant when more than one nitro moiety is present at the same carbon, and it can amount to an increase in the coupling of 7 Hz, i.e. by about 20% with respect to a typical value of 35 Hz which is characteristic of unsubstituted alkanes. The effect is comparable to that exerted by chlorine substituents, but is smaller than those induced by hydroxy or alkoxy oxygen atoms and by fluorine. The results for nitroalkanes seem to suggest that a major factor in substituent-induced effects on 1J(CC)s across a single bond is the electronegativity of the atoms which are attached directly to the bond, but some effects induced by methyl substituents suggest a contribution from steric hindrance. Semi-empirical calculations by the TNDO/2 method reproduced satisfactorily the general trends observed in substituent effects on 1J(CC)s, including those exerted by nitro groups. © 1998 John Wiley & Sons, Ltd.

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.

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.

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.

Dioxomolybdenum(VI) complexes with 2α-hydroxybenzimidazoles and their 95Mo NMR spectra

Complexes of a series of 2α-hydroxybenzimidazoles (L) with Mo(VI) are reported. In most cases the complexes form readily on reaction of MoO2(AcAc)2 with L in acetone or ethanol. Electronic spectra, infra red spectra, magnetic measurements, 1H and 95Mo NMR results are reported for the complexes which have MoO2L2 or MoO2L2(Solvent)1, stoichiometry. The physical measurements are best interpreted in terms of distorted octahedral cis-dioxoMo(VI) complexes with a 4O, 2N donor set. This is confirmed for the complex with 2α-hydroxybenzylbenzimidazole (HBB) by an X-ray crystallographic study which also shows that HBB coordinates through its imino nitrogen and alkoxy oxygen atoms.

NN′-dialkoxy-NN′-bis(trifluoromethyl)hydrazines, novel products from the reaction of alkoxyl radicals with trifluoronitrosomethane

Alkoxyl radicals, generated by nitrite photolysis, react with trifluoronitrosomethane to yield NN′-dialkoxy-NN′-bis-(trifluoromethyl)hydrazines. An 18O-labelling experiment indicated complete retention of the alkoxy-oxygen atom. When the products are heated with thioglycolic acid, cracking leads to the hydroxylamines, RO·NH·CF3. For the case where R is 1-adamantyl, further stepwise conversion into O-(1-adamantyl)hydroxylamine has been achieved.

Alkyl Inductive Effects on Molecular Ionization Potentials. XVI. Esters

Correlation of molecular ionization potentials, E1, with Taft's alkyl inductive substituent constants, σ1(R), has now been extended to include the esters. It is found that three series of esters, the formates, acetates, and methyl alkanoates, fall on three separate straight lines in accord with the general equation E1 = E0 + a1σ1(R), where E0 is the intercept and a1 the slope. The average standard error for the three lines is 0.024 eV with an average correlation coefficient of 0.992, showing that the alkyl substituent exerts an inductive influence on the electron density at the site suffering the electron loss: a lone pair on either the carbonyl or alkoxy oxygen atom. Evidence is deduced for the site of electron expulsion and a prediction is made concerning the site of vapor phase protonation of esters and carboxylic acids. E1 values presently not available experimentally are predicted for several esters.

Reactivity of groups attached to reduced cyclic ring systems—I : Kinetics of the menschutkin reaction of 3-dimethylaminomethyl steroids with methyl iodide, and consideration of the reasons for the observed differential rates in some other reactions at epimeric axial and equatorial grousps

In contrast to the previously examined 2 epimeric dimethylamino steroids, spimeric dimethylaminomethyl steroids (containing the group CH 2NMe 2) react at approximately the same rates with methyl iodide in nitrobenzene-benzene. This observation is significant for the consideration of differential reactivity in other reactions with epimeric axial-equatorial pairs: the relative ease of hydrolysis of esters of epimeric axil and equatorial alcohols, for example, is probably due mainly to differential hindrance to solvation at the relevant alkoxy oxygen atoms during reaction.