
	Where results make sense

Topic: Steric effects

In the News (Thu 16 Feb 12)

EXECUTIVE POWER

Iran

ANALYSIS

Pakistan

Family compact

	Reference.com/Encyclopedia/Steric effects
		Steric shielding occurs when a charged group on a molecule is seemingly weakened or spatially shielded by less charged (or oppositely charged) atoms, including counterions in solution (Debye shielding).
		In chemistry, steric effects are nearly universal and affect the rates and energies of most chemical reactions to varying degrees.
		In biochemistry, steric effects are often exploited in naturally occurring molecules such as enzymes, where the catalytic site may be buried within a large protein structure.
	www.reference.com /browse/wiki/Steric_effects (415 words)

	Steric effects - Wikipedia, the free encyclopedia
		Steric shielding occurs when a charged group on a molecule is seemingly weakened or spatially shielded by less charged (or oppositely charged) atoms, including counterions in solution (Debye shielding).
		In chemistry, steric effects are nearly universal and affect the rates and energies of most chemical reactions to varying degrees.
		In biochemistry, steric effects are often exploited in naturally occurring molecules such as enzymes, where the catalytic site may be buried within a large protein structure.
	en.wikipedia.org /wiki/Steric_effects (431 words)

	Inquiry
		Since increased steric hindrance is associated with branching, and since branching of a carbon skeleton is known to lower boiling points, care will be needed to separate that effect from steric effects on the OH group.
		That is to say that the steric effects are the same for alkanes and alcohols (relative proportions, that is).
		Once again it is seen that boiling points are effected in the same proportion and therefore it is further concluded that the steric hindrance has no direct effect on the hydrogen bonding of the alcohols.
	www.sas.upenn.edu /~mpilarz/inquiry.html (918 words)

	[No title]
		Steric Strains as a Factor in the Relative Stability of Some Etherates of Boron Fluoride.
		1951 Effect of Structure on the Relative Reactivities of Hydrogen Atoms as Determined in Photochemical Halogenations.
		Boyd, Alfred C. 1953 The Effect of the Halogen on the Rate of Solvolysis of the p-Halophenyl Dimethyl Carbinal Chlorides.
	www.chem.purdue.edu /hcbrown/Theses.htm (1644 words)

	C&EN: NEWS OF THE WEEK - STRUCTURAL ANALYSIS
		It turns out, however, that steric effects are only of secondary importance.
		In fact, by themselves steric effects favor the eclipsed conformation.
		New calculations by chemistry professor Lionel Goodman and graduate student Vojislava T. Pophristic of Rutgers University show instead that hyperconjugation, a quantum-mechanical effect involving the transfer of electrons from an occupied orbital to an unoccupied orbital, causes ethane to adopt its preferred conformation [Nature, 411, 565 (2001)].
	pubs.acs.org /cen/topstory/7923/7923notw3.html (366 words)

	St to Sy and sigma
		The steric effect in a reaction is ascribed to the difference in steric energy between, on the one hand, reactants and, on the other hand, a transition state, (or products).
		(The adjective "steric" is not to be confused with stereochemical.)
		Steric effects arise from contributions ascribed to strain as the sum of (1) non-bonded repulsions, (2) bond angle strain, and (3) bond stretches or compressions.
	www.chem.qmul.ac.uk /iupac/gtpoc/StSy.html (2239 words)

	[No title]
		Calculations required for steric effects are relatively simple (in principle) and can be carried out completely where sterics dominate.
		Whenever there is severe steric interference between atoms or groups of atoms, the strain can be partially relieved by deformation of valence angles, to allow atoms to move apart.
		Assume a principle that stretching of valence bonds contributes little to the relief of steric strain; the major effects are those of bond bending.
	www.sdsc.edu /~kimb/aromatics.html.txt (571 words)

	proposal for dft study of Rh dimers
		In addition to extending and completing the steric effect studies, an attempt will be made to model the transition state for the addition of a carbene to a C=C double bond.
		Steric Effects: Much remains to be done to investigate the steric effects that may influence the course of the carbene insertion reaction.
		The biological effects of the group depend on the relative orientation of the other atoms bonded to the carbons; this relative orientation is the stereochemistry of the ring.
	www.acs.appstate.edu /~willsd/NCSCPR5.HTML (4211 words)

	README
		These calculations are seen to be most useful in organometallic chemistry, where steric effects of ligands about a metal are of interest, and the chemistry of reactions where steric effects in groups reacting at points are of interest.
		This is a far more systematic parameter for describing the angular steric size of a ligand than is the cone angle, and refers to the angular area around the metal that is occupied by the ligand.
		The steric command files and the steric parameter files are identified by having the lines "#steric" and "#sterpar" as their first lines repectively.
	www.ccl.net /cca/software/SOURCES/C/steric/README.shtml (1990 words)

	Effects of plasma proteins on sieving of tracer macromolecules in glomerular basement membrane -- Lazzara and Deen 281 ...
		The effects of native and modified bovine serum albumin on the permeability of frog mesenteric capillaries.
		Effect of concentration on the rejection coefficients of rigid macromolecules in track-etch membranes.
		Watson, PD. Effects of blood-free and protein-free perfusion on CFC in the isolated cat hindlimb.
	ajprenal.physiology.org /cgi/content/full/281/5/F860 (5075 words)

	Aims And Objectives
		Fluoro substituents are the smallest substituents that can replace hydrogen in a liquid crystal core unit, yet combinations of the subtle steric effects and the high electronegativity of fluorine can have dramatic effects on the melting point, transition temperatures, mesophase morphology, and clearing points of liquid crystalline units.
		Substitution by one or two fluorine’s has been attempted in the past and it has been noted that the slight disruption in the lamella packing caused by the subtle steric effects is conducive to nematic phase generation, though this is sometimes at the expense of smectic phase stability.
		The precise effects of the substitution varies quite significantly, which when considered is not really that surprising since there is the possibility of the steric effects being shielded within the molecule, or the issues of molecular broadening and inter annular twisting could play very important roles.
	www.hull.ac.uk /php/ch0pjs/Aims_and_objectives.htm (476 words)

	QSAR and Drug Design (Site not responding. Last check: 2007-10-16)
		It relates the effect of substituents on that equilibrium to the effect of those substituents on the benzoic acid equilibrium.
		In the aniline and phenol equilibria, the hydrogen ion that is dissociating is one atom removed from the phenyl ring, whereas in the benzoic acid equilibrium it is two atoms removed.
		For a nitro group in the meta position, electron-withdrawal is due to an inductive effect produced by the electronegativity of the constituent atoms.
	www.biochem.vt.edu /modeling/qsar_drug.html (3804 words)

	Steric Effects on Multivalent Ligand-Receptor Binding: Exclusion of Ligand Sites by Bound Cell Surface Receptors -- ...
		quantify the effects of steric hindrance on ligand-receptor kinetics
		In the absence of steric effects, H(i) = 1, because
		Steric effects on equilibrium and kinetic binding are
	www.biophysj.org /cgi/content/full/76/6/3031 (5852 words)

	BioMed Central \| Full text \| Electronic properties of amino acid side chains: quantum mechanics calculation of ...
		Second, steric effects are known to encourage proton dissociation and lower the pKa [25].
		The significance of these effects should not be underestimated because studies have shown that inductive effects extend across non-conjugated bonds in proteins [30] and may even affect electron density over a distance of several residues [52].
		The behavior of the hydroxyl moiety (bond lengths and Mulliken populations) in substituted cyclohexanol and phenol was evaluated as an indicator of the substituent effects of the side chains.
	www.biomedcentral.com /1472-6769/5/2 (6192 words)

	DilfluoroProj
		This is a reasonable finding since the two groups are about the same size and thus steric effects are approximately the same between two identical groups on a molecule as compared to steric effects of two identical molecules of similar size.
		The energy difference is slightly higher on the butane because although any steric effects on both are minimal, there is still some torsional effects from the methyl hydrogens and other hydrogens on the molecule.
		On the difluoroethane molecule there is no torsional effects (since there are no methyl groups), thus there is only the steric effects of the fluorine and hydrogen, which proves to be a much smaller repulsion than the effects of the methyl-hydrogen interactions discussed in the butane.
	www.sas.upenn.edu /~mpilarz/difluoro.html (715 words)

	C&EN: NEWS OF THE WEEK - STERIC, SOLVENT EFFECTS UNCOUPLED
		Steric effects reasonably explain the differing rates of certain reactions.
		But the rate changes that occur when one substituent is replaced with a bulkier one have all been attributed to steric effects, because separating those effects from solvation effects has been impossible.
		Furthermore, the calculated difference is of the same magnitude as the discrepancy in the measured steric effects for gas- and solution-phase reactions.
	pubs.acs.org /cen/topstory/8012/8012notw4.html (495 words)

	science-sn2-descrip.html
		But separating the effects of solvation from the repulsive interactions (the steric effect) has challenged chemists for over a century (1-3).
		The barrier that separates these complexes provides a direct measure of the steric effect in the reaction, after correction for differences in the bond strengths of the forming and breaking bonds.
		The magnitude of this intrinsic barrier increase (attributable to the increased steric effect as t-butyl is substituted for methyl on the reactive carbon center) is about one-quarter of the barrier increase observed in aqueous solution.
	mc2.cchem.berkeley.edu /Organic/Chem226/Announcements-info/science-sn2-descrip.html (1010 words)

	P and Q
		The lifetime of a radical is profoundly influenced by steric shielding of the radical centre by bulky substituents.
		Sometimes, however, the term "polar effect" is taken to refer to the influence, other than steric, that non-conjugated substituents exert on reaction rates, i.e.
		effects connected with electron delocalization between a substituent and the molecular framework to which it is attached are excluded.
	www.chem.qmw.ac.uk /iupac/gtpoc/PQ.html (1935 words)

	Hammond Publications
		"Steric Effects in Aromatic Substitution", with M.F. Hawthorne, Chapter in "Steric Effects in Organic Chemistry", M.S. Newman, Editor, John Wiley and Sons, Inc. (1956).
		Cage Effects in the Decomposition of a, a'-Azoisobutyronitrile and Related Compounds.
		"The Effect of Cumyl Hydroperoxide on the Behavior of Oxidation Inhibitors.
	chem.pdx.edu /~wamserc/Hammond/pubs.htm (4331 words)

	MSK Homepage: Welcome
		Our work focuses on the qualitative effects, meaining that we are working on an improvement of the standard models of the electrochemistry while trying to remain as simple as possible, but not simpler.
		Steric effects imply a non-monotonic surface capacitance and reduced salt adsorption.
		Kilic, M. Bazant and A. Ajdari, Steric Effects in Dynamics of Electrolytes II: Modified Poisson-Nernst-Planck Equations, Phys.
	web.mit.edu /mskilic/www (333 words)

	Ligand Migration in Human Myoglobin: Steric Effects of Isoleucine 107(G8) on O2 and CO Binding -- Ishikawa et al. 80 ...
		The minor effects of the mutations at Ile107 on the heme environmental
		The effects of amino acid substitution at position E7 (residue 64) on the kinetics of ligand binding to sperm whale myoglobin.
		The effects of heme pocket hydrophobicity on the ligand binding dynamics in myoglobin as studied with leucine 29 mutants.
	www.biophysj.org /cgi/content/full/80/3/1507 (5442 words)

	science-sn2-article.html
		that steric effects in the gas phase are diminished relative to
		Increasingthe size of the substituents, R, decreases the rate of the reactionby creating nonbonded interactions (steric effects) that raisethe energy of the transition state.
		The idea of a steric effect was first proposed by Hofmann (1, 2) 130 years ago, but a quantitative understandingof this effect in the S
	mc2.cchem.berkeley.edu /Organic/Chem226/Announcements-info/science-sn2-article.html (1489 words)

	[No title]
		The Composition of the Steric Parameter as a Function of Alkyl Branching.
		The Cumulative Effect of Substituents and the Solvent Dependence of the Hammett Reaction Constants.
		Contributions of Steric, Electrical and Polarizability Effects in Enantioselective Hydrolyses with Rhizopus nigricans: A Quantitative Analysis.
	pratt.edu /~mcharton/bio.html (2537 words)

	An electronic effect on protein structure -- Hinderaker and Raines 12 (6): 1188 -- Protein Science
		that steric effects alone are not the sole determinant of the
		that steric effects are manifested in amides 1–3.
		Panasik Jr., N., Eberhardt, E.S., Edison, A.S., Powell, D.R., and Raines, R.T. Inductive effects on the structure of proline residues.
	www.proteinscience.org /cgi/content/full/12/6/1188 (3042 words)

	Imine Formation
		This kind of explanation uses steric effects, effects on a reaction which arise from the size of atoms or groups.
		The structural difference between these two cases is the electronegativity difference between H and F. Consider that the carbonyl carbon is already somewhat electron deficient since it is associated with the more electronegative oxygen and two of its valence electrons are relatively far away in a pi orbital.
		Keep in mind that steric effects involve changes in size between comparable situations, and polar effects involve changes in electronegativity or similar electronic characteristics.
	chemistry2.csudh.edu /rpendarvis/imineformF99.html (2072 words)

	Steric: A program to calculate molecular steric effects
		Steric effects in molecular packing in the solid state.
		The radial profile calculation calculates the solid angle (or alternative steric parameter) of the intersection between the molecule and a sphere of a particular radius about the point of perspective.
		This calculation can be performed on all steric parameters, including numerical volume, whereas the radial profile cannot be performed on the volume, for obvious reasons.
	www.gh.wits.ac.za /craig/steric (453 words)

	Improved Algorithm for Accurate Computation of Molecular Solid Angles
		In 1977 the cone angle was introduced by Tolman for the quantification of the steric size of molecular fragments about a point, such as a ligand about a metal atom in a complex [1].
		The repetition of this calculation for a range of radii that cover the entire molecule yields the solid angle radial profile, which is useful for the determination of the radial dependence of the steric size of the molecular fragment.
		It is also possible to use the algorithm for the calculation of the average solid angle of a set of conformers generated from molecular mechanics calculations [5].
	www.gh.wits.ac.za /craig/steric/multisol/html/multisol.html (5172 words)

	Molecular Chemistry Takes a New Twist: Science News Online, June 2, 2001 (Site not responding. Last check: 2007-10-16)
		First, she mathematically modeled ethane and removed the parts of the calculations that relate to the steric effect.
		Hyperconjugation, not steric effects, makes staggered ethane stable, they conclude.
		Hyperconjugation not steric repulsion leads to the staggered structure of ethane.
	www.sciencenews.org /20010602/fob1.asp (546 words)

	ACD/pKa DB: Technical Information
		In most cases steric effects have been taken into account by defining the ionization center as an ionizable functional group with a sufficiently large invariable skeleton.
		In cases where the variable substituents are in close proximity to ionizable groups, steric effects are calculated by the modified branching equations.
		In the cases when the charged substituent is variable its effect is calculated from the distance to ionization center.
	www.acdlabs.com /products/phys_chem_lab/pka/tech3.html (409 words)

Try your search on: Qwika (all wikis)