Results 201 to 210 of about 147,337 (257)

Steric hindrance of acetophosphides

Bulletin of the Academy of Sciences of the USSR Division of Chemical Science, 1968
1. The introduction of a bulky substituent at the carbonyl group in acetophosphides invokes steric hindrance to the existence of the cis isomer. 2. The low-frequency peak νCO in the IR spectra of acetophosphides is due to the trans isomer.
R. G. Kostyanovskii, V. V. Yakshin, S. L. Zimont, I. I. Chervin   +3 more
openaire   +1 more source

Quantum Mechanical Size and Steric Hindrance

The Journal of Physical Chemistry A, 2006
A quantum mechanical definition of molecular size and shape is formulated from the electronic second moment of the Hartree-Fock wave function. The shape tensor is defined to be invariant with respect to the origin. The geometric average of the eigenvalues of the tensor correlates very well with van der Waals and Bragg-Slater radii.
Joshua W, Hollett, Aaron, Kelly, Raymond A, Poirier   +2 more
openaire   +2 more sources

Calculation of Steric Hindrance

Nature, 1942
IT seems possible to account for the steric effect of non-reacting groups on substitution rates on the lines of the following scheme, illustrated here by the example of the symmetrical substitution of t-butyl chloride by chlorine ions: In the transition state, the four t-butyl carbons will be co-planar and the methyl groups will cause least obstruction
A. G. EVANS, M. POLANYI
openaire   +1 more source

STERIC HINDRANCE AND HEATS OF FORMATION

Nature, 1943
IN the low-temperature polymerization of isobutene by boron fluoride, BF3, the heat of polymerization, which has been found to be in the neighbourhood of 10 kcal. per mole, is lower than would be expected on the basis of theoretical calculations1. Both chemical1 and X-ray2 evidence support the head-to-tail chain-structure:
A. G. EVANS, M. POLANYI
openaire   +1 more source

Origin of steric hindrance in ethane

International Journal of Quantum Chemistry, 1994
AbstractSteric hindrance has been regarded as a result of nonbonding atomic repulsion and measured in terms of empirically obtained van der Waals radii. The authors sought the cause of steric hindrance using the partial derivatives of the energy‐components with respect to a nuclear coordinate.
Hiroaki Tokiwa, Hiroshi Ichikawa
openaire   +1 more source

The origin of steric hindrance in cyclohexane derivatives

Experientia, 1953
Aus der Veresterungsgeschwindigkeit der stereoisomeren Menthole mitp-Nitrobenzoylchlorid lasst sich schliessen, dass diese Molekule in derjenigen Konstellation reagieren, in welcher die Oxygruppe eine aquatoriale Stellung einnimmt. In starren Molekulen (wie dietrans-Dekalole), bei denen die Verschiebung einer Oxyoder Estergruppe von der polaren in die ...
openaire   +2 more sources

STRIDER: Steric hindrance and metal coordination identifier

Computational Biology and Chemistry, 2022
Biomolecular structural knowledge is important to understand the biological processes and the mechanisms underlying human diseases. In silico modeling plays a vital role in de novo design and docking of biomacromolecules as well as in exploring their conformational dynamics.
L. Ponoop Prasad Patro, Thenmalarchelvi Rathinavelan   +1 more
openaire   +3 more sources

Inhibition of Nitrosation by Steric Hindrance

Journal of Agricultural and Food Chemistry, 1997
The nitrosation of piperidine, 2-methylpiperidine, 4-methylpiperidine, 2,6-dimethylpiperidine, and 2-ethylpiperidine in acid medium was studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the nitrosamine formed at λ = 249 nm.
Samuel González-Mancebo, Emilio Calle, M. Pilar García-Santos, Julio Casado   +3 more
openaire   +1 more source

Steric hindrance in acetamidomesitylene

Journal of Applied Chemistry, 1951
AbstractThe acetyl group of acetamidomesitylene is not split off either by acids or by alkalis under analytical conditions. A laboratory preparation of acetamidomesitylene is described.
openaire   +1 more source

Steric Hindrance in Vinyl-Mesitylene

Nature, 1948
A NUMBER of workers have observed various anomalous properties in nuclear-substituted derivatives of mesitylene, such anomalies usually being ascribed to restricted rotation about the bond connecting the substituent to the benzene ring caused by the two ortho-methyl - groups.
F. R. BUCK, G. T. KENNEDY, F. MORTON, E. M. TANNER   +3 more
openaire   +1 more source