The mechanism of [1,3] o to n acyl migrations : A mndo scf-mo study

MNDO SCF-MO calculations suggest that the uncatalysed rearrangements of 0-acyl imidates ($\text{1}$) to the corresponding imides ($\text{2}$) are concerted reactions involving synchronous C-N bond formation and C-O bond cleavage. The calculated dipole moment and atomic charges in the transition state are consistent with the properties of these reactions in solution. The transition states for [1,3] acyl migrations in compounds such as $\text{3}$ which have no lone pair of electrons are predicted to have significantly different properties.     

Rotational isomerism between the E and Z forms of o-substituted benzo-N-methyl hydroxamic acids in strong acid

The $\text{E}$∠$\text{Z}$ equilibrium of the cations of benzo hydroxamic acids, in mineral acid, was studied utilizing ¹H NMR spectroscopy, NOEDS and MNDO claculations     

Does the boat-like conformer exist for 1,8,8-trimethylbicyclo[3.2.1]Octan-3-one?

Neither molecular mechanics (MM2 and MM2′) nor molecular orbital (MNDO and $\text{ab}$$\text{initio}$) calculations confirmed the existence of a boat-like conformer for the title compound, recently proposed to exist up to 20% in hydrocarbon solvents based on the CD spectra.     

An STO-3G investigation of barriers to rotation in model systems for aromatic polycarbonates

Non-empirical, STO-3G, and semi-empirical, MNDO, calculations have been performed to investigate the rigid rotation of the phenyl group in phenyl carbonic acid, as a model for Bisphenol A polycarbonate. The MNDO results predict a barrier to rotation of ～55 kcal mole^?1, a factor of ～2 greater than that for the STO-3G computations. Analysis of the relevant orbital energies dictates that the lowest excited state of phenyl carbonic acid is $\text{π → π}{}^1$.     

Alternative mechanisms for cyanide anion exchange with acetonitrile

Mechanisms for the recently observed exchange of cyanide anion in acetonitrile have been investigated by means of semi-empirical MNDO molecular orbital calculations. A prototropic type mechanism $\text{via}$ a cyclopropane intermediate is the most likely candidate. The previously proposed concerted migration is indicated to be the least favourable reaction pathway.     

Conformation and rotational barriers of 2-substituted 1,3-diphenylallyl anions

The conformations and the rotational barriers of the 2-substituted 1,3-diphenylallylanions $\text{1b}$–$\text{g}$ (Tab. 2) have been determined. Increasing size of the substituents leads to more $\text{exo}$,$\text{endo}$- and $\text{endo}$,$\text{endo}$-conformers at the cost of the $\text{exo}$,$\text{exo}$-species. This trend is connected with decreasing ΔG³-value sof the rotational barriers; the barriers are essentially not affected by ion pair effects, which is in contrast to the parent “allyl anion”.     

Nucleophilic reaction of fluoroolefins. V. Regioselectivity and stereochemistry in the reactios of 1-phenylpentafluoropropenes with lithium dialkylamides

1-Phenylpentafluoropropenes $\text{1}$ readily react with lithium dialkylamides to give, in most cases, mixtures of 1-aminosubstituted alkenes $\text{2}$ and 2-amino-substituted alkenes $\text{3}$, with the latter being the favoured products. The reactions with bulky lithium diethylamide and lithium 2-methylpiperidinoamide gave exclusively 1-amino-substituted products $\text{2}$. The effect of the increased bulk of N-nucleophiles is opposite to that observed for the reactions of alkenes $\text{1}$ with C-nucleophiles Increasing electronegativity of the phenyl ring substituents in alkenes $\text{1}$ shifts the regioselectivity of the attack of lithium amides towards the C2 carbon atom. The E to Z isomer ratios of enamines $\text{2}$ were found to be time dependent and the slow isomerisation of the kinetic isomers E to the thermodynamic isomers Z was observed, while the ratio of isomers of enamines $\text{3}$ did not change with time.A concerted, single-step process is suggested for the reactions of alkenes $\text{1}$ with lithium dialkylamides, and a tentative explanation of the different stereochemistry of enamines $\text{2}$ and $\text{3}$ is given.     

Geometries and rotational barriers of alkylamides and lithium alkylamides.

The barriers to rotation of methylamide, ethylamide and the corresponding lithium amides have been computed at the $\text{ab}$$\text{initio}$ 4-31G level. The barriers to rotation about the CN bond are higher for amides than for amines, but are lowered by coordination with Li⁺.     

Stereochemistry of the reactions of pinacol allylboronate with two α,β-dialkoxyaldehydes

The stereochemistry of the reactions of pinacol allylboronate $\text{5}$ with α,β-dialkoxyaldehydes $\text{3}$ and $\text{4}$ is described. The results are contrasted with data for the reactions of crotylboronates $\text{1}$ and $\text{2}$ with the same aldehydes.     

Non-hydrodynamic contribution to the concentration dependence of the self diffusion of interacting brownian macroparticles

One-dimensional single-channel scattering calculations on an effective potential are used to discuss resonances in collinear reactions and to predict their energetic location almost quantitatively. The effective potential includes the vibrationally adiabatic potential and the adiabatic diagonal correction in Delves' mass-weighted polar coordinates (hyperspherical coordinates). This $\text{di}$agonal corrected $\text{v}$ibrational $\text{a}$diabatic $\text{h}$yperspherical (DIVAH) model is tested for a variety of reactions (H + H₂, H + MuH, I + HI, F + H₂) and a detailed discussion of the effective potential and its physical implications is given.     

Stereochemical studies—971a. Saturated heterocycles—991b : An unusual ring-opening reaction of 2-methylthio-3,1-perhydro-benzoxazines. A comparative study of the 3,1 and 1,3-isomers

In the reactions of 2-thioxo-$\text{cis}$- and $\text{trans}$-3,1-perhydrobenzoxazines ($\text{3}$, $\text{4}$) with methyl iodide the hydrogen iodide formed in the S-methylation process brings about ring-opening and gives iodomethylthiolcarbamates ($\text{7}$, $\text{8}$). Under similar conditions, the thioether salts ($\text{15}$, $\text{16}$) of the structurally isomeric $\text{cis}$- and $\text{trans}$-2-thioxo-1,3-perhydrobenzoxazines, corresponding to the unstable intermediates in the former reactions, are stable. Under more vigorous conditions, the $\text{cis}$ isomer thioether salt $\text{15}$ is transformed into the corresponding $\text{cis}$-and $\text{trans}$-l,3-perhydrobenzoxazin-2-ones ($\text{17}$, $\text{18}$) by ring-opening and subsequent ring-closure, whereas the $\text{trans}$ isomer $\text{16}$ gives only $\text{trans}$-1,3-perhydrobenzoxazin-2-one ($\text{18}$).     

Substituent effects on carbohydrate coupling reactions promoted by insoluble silver salts

Coupling reactions were performed in the α-D-glucopyranosyl bromide series (i.e. compounds $\text{1}$ a–c, $\text{2}$ a, b, $\text{3}$ and $\text{4}$) and the α-D-mannopyranosyl bromide series (i.e. compounds $\text{7}$ a–c, $\text{8}$ a, b, $\text{9}$) with aglycons $\text{5}$ or $\text{10}$ in the presence of insoluble silver salt promotors. (i.e. silver silicate and silver zeolite). The insoluble silver salt promotes the formation of the β-glycosidic linkage, while a non-participating group is present at C-2 of the glycon. It was found that in both series 4-O-acyl functions increase the β/α ratio of the glycosidic bond formation relative to 4-O-alkyl functions, whereas 3-O and 6-O-acyl functions decrease this ratio. We assume that inductive effects are responsible for the influence exerted by 3-O-substituents, but that through-bond interactions are essential for the effects exerted by 4-O and 6-O substituents. Another unexpected finding was that coupling of α-D-mannopyranosyl bromide derivatives gave much higher β/α ratios than the corresponding reactions of α -D-glucopyranosyl bromides.     

The effect of ortho substituents in SRNl reactions. Some synthetic applications

Several $\text{ortho}$-substituted iodobenzenes were allowed to react, via the S_RNl mechanism, with mixtures of diethyl phosphite ion and pinacolone enolate ion. From product composition data, the relative reactivities of the two nucleophiles were reckoned. They represent relative reactivities in attachment to aryl radical intermediates. Most of the $\text{ortho}$ effects are slight, but there is evidence that large $\text{ortho}$ substituents hinder attachment of the phosphite more than the enolate nucleophile. The methoxy and diethoxyphosphoryl substituents, when $\text{para}$ to the site of substitution, respectively favour and disfavour the phosphite with respect to the enolate ion. S_RNl reactions of $\text{ortho}$-substituted halobenzenes are, for some substituents, followed by other reactions which afford products of synthetic interest.     

Stereochemistry in trivalent nitrogen compounds. 40. Torsional barriers in N-2,4-dinitrobenzenesulfenylbenzimidazoles.

N-2,4-Dinitrobenzenesulfenylbenzimidazoles exhibit substantial barriers to torsion about the sulfur-nitrogen bond ($\text{ca}$ 19 kcal/mole).     

Carbon-carbon bond formation between alkylated alkenes and acrylic ester via 2-methoxyalkyl radicals

Methoxymercuration/demercuration reactions of alkenes 10 in $\text{10}$ in the presence of acrylic ester yield products $\text{11}$ in a carbon-carbon bond formation reaction.     

Cycloaddition reactions of 1,3-benzothiazines - 6. Reactions of 1,3-benzothiazine derivatives with substituted acetyl chlorides

6, 7-Dimethoxy-2$\text{H}$-l,3-benzothiazine derivatives ($\text{1}$, $\text{8}$) react with substituted acetyl chlorides to give angularly condensed β -lactams ($\text{3a}$-$\text{d}$, $\text{10}$, $\text{11}$). The $\text{cis}$ compound $\text{11}$ was epimerised to the $\text{trans}$ derivative $\text{12}$. From the interaction of 2-phenyl-6,7-dimethoxy-4$\text{H}$-1,3-benzothiazine ($\text{7}$) and α -chloro-phenylacetyl chloride two stereoisomeric β -lactam derivatives ($\text{9a}$, $\text{b}$) were isolated, whereas in the other cases studied the reactions leading to β -lactams proved to be stereospecific. Analogous reactions of $\text{4}$-methyl-6,7-dimethoxy-2$\text{H}$-l,3-benzothiazine ($\text{5}$) furnished the enamides $\text{6a}$,$\text{c}$, $\text{d}$. Structures of the new compounds and configurations of the diastereomers were elucidated by IR and NMR spectroscopy.