Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape (conformation) and reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel.
The parent cyclobutadiene (R = H) readily dimerizes but the R = tert-butyl derivative is robust.[1]
Regioselective dimethoxytritylation of the primary 5'-hydroxyl group of thymidine in the presence of a free secondary 3'-hydroxy group as a result of steric hindrance due to the dimethoxytrityl group and the ribose ring (Py = pyridine).[2]
Steric hindrance is a consequence of steric effects. Steric hindrance is the slowing of chemical reactions due to steric bulk. It is usually manifested in intermolecular reactions, whereas discussion of steric effects often focus on intramolecular interactions. Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions.
Steric hindrance between adjacent groups can also affect torsional bond angles. Steric hindrance is responsible for the observed shape of rotaxanes and the low rates of racemization of 2,2'-disubstituted biphenyl and binaphthyl derivatives.
Measures of steric propertiesedit
Because steric effects have profound impact on properties, the steric properties of substituents have been assessed by numerous methods.
Rate dataedit
Relative rates of chemical reactions provide useful insights into the effects of the steric bulk of substituents. Under standard conditions, methyl bromide solvolyzes 107 faster than does neopentyl bromide. The difference reflects the inhibition of attack on the compound with the sterically bulky (CH3)3C group.[3]
A-valuesedit
A-values provide another measure of the bulk of substituents. A-values are derived from equilibrium measurements of monosubstituted cyclohexanes.[4][5][6][7] The extent that a substituent favors the equatorial position gives a measure of its bulk.
The A-value for a methyl group is 1.74 as derived from the chemical equilibrium above. It costs 1.74 kcal/mol for the methyl group to adopt to the axial position compared to the equatorial position.
Substituent
A-Value
H
0
CH3
1.74
CH2CH3
1.75
CH(CH3)2
2.15
C(CH3)3
>4
Ceiling temperaturesedit
Ceiling temperature () is a measure of the steric properties of the monomers that comprise a polymer. is the temperature where the rate of polymerization and depolymerization are equal. Sterically hindered monomers give polymers with low 's, which are usually not useful.
Steric effects are critical to chemistry, biochemistry, and pharmacology. In organic chemistry, steric effects are nearly universal and affect the rates and activation 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. In pharmacology, steric effects determine how and at what rate a drug will interact with its target bio-molecules.
An isolable selenenic acid owing to steric protection.[14]
The steric effect of tri-(tert-butyl)amine makes electrophilic reactions, like forming the tetraalkylammonium cation, difficult. It is difficult for electrophiles to get close enough to allow attack by the lone pair of the nitrogen (nitrogen is shown in blue)
^Günther Maier; Stephan Pfriem; Ulrich Schäfer; Rudolf Matusch (1978). "Tetra-tert-butyltetrahedrane". Angew. Chem. Int. Ed. Engl. 17 (7): 520–1. doi:10.1002/anie.197805201.
^Gait, Michael (1984). Oligonucleotide synthesis: a practical approach. Oxford: IRL Press. ISBN0-904147-74-6.
^Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN978-0-471-72091-1
^E.L. Eliel, S.H. Wilen and L.N. Mander, Stereochemistry of Organic Compounds, Wiley, New York (1994). ISBN81-224-0570-3
^Hirsch, J.A. (1967). Topics in Stereochemistry (first ed.). New York: John Wiley & Sons, Inc. p. 199.
^Romers, C.; Altona, C.; Buys, H.R.; Havinga, E. (1969). Topics in Stereochemistry (fourth ed.). New York: John Wiley & Sons, Inc. p. 40.
^Stevens, Malcolm P. (1999). "6". Polymer Chemistry an Introduction (3rd ed.). New York: Oxford University Press. pp. 193–194. ISBN978-0-19-512444-6.
^Tolman, Chadwick A. (1970-05-01). "Phosphorus ligand exchange equilibriums on zerovalent nickel. Dominant role for steric effects". J. Am. Chem. Soc.92 (10): 2956–2965. doi:10.1021/ja00713a007.
^Stephan, Douglas W. "Frustrated Lewis pairs": a concept for new reactivity and catalysis. Org. Biomol. Chem. 2008, 6, 1535–1539. doi:10.1039/b802575b
^Pieter Gijsman (2010). "Photostabilisation of Polymer Materials". In Norman S. Allen (ed.). Photochemistry and Photophysics of Polymer Materials Photochemistry. Hoboken: John Wiley & Sons. pp. 627–679. doi:10.1002/9780470594179.ch17. ISBN978-0-470-59417-9..
^Klaus Köhler; Peter Simmendinger; Wolfgang Roelle; Wilfried Scholz; Andreas Valet; Mario Slongo (2010). "Paints and Coatings, 4. Pigments, Extenders, and Additives". Ullmann's Encyclopedia Of Industrial Chemistry. pp. o18_o03. doi:10.1002/14356007.o18_o03. ISBN978-3-527-30673-2.
^Goto, Kei; Nagahama, Michiko; Mizushima, Tadashi; Shimada, Keiichi; Kawashima, Takayuki; Okazaki, Renji (2001). "The First Direct Oxidative Conversion of a Selenol to a Stable Selenenic Acid: Experimental Demonstration of Three Processes Included in the Catalytic Cycle of Glutathione Peroxidase". Organic Letters. 3 (22): 3569–3572. doi:10.1021/ol016682s. PMID 11678710.
steric, effects, arise, from, spatial, arrangement, atoms, when, atoms, come, close, together, there, generally, rise, energy, molecule, nonbonding, interactions, that, influence, shape, conformation, reactivity, ions, molecules, complement, electronic, effect. Steric effects arise from the spatial arrangement of atoms When atoms come close together there is generally a rise in the energy of the molecule Steric effects are nonbonding interactions that influence the shape conformation and reactivity of ions and molecules Steric effects complement electronic effects which dictate the shape and reactivity of molecules Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel The parent cyclobutadiene R H readily dimerizes but the R tert butyl derivative is robust 1 Contents 1 Steric hindrance 2 Measures of steric properties 2 1 Rate data 2 2 A values 2 3 Ceiling temperatures 2 4 Cone angles 3 Significance and applications 4 See also 5 References 6 External linksSteric hindrance edit nbsp Regioselective dimethoxytritylation of the primary 5 hydroxyl group of thymidine in the presence of a free secondary 3 hydroxy group as a result of steric hindrance due to the dimethoxytrityl group and the ribose ring Py pyridine 2 Steric hindrance is a consequence of steric effects Steric hindrance is the slowing of chemical reactions due to steric bulk It is usually manifested in intermolecular reactions whereas discussion of steric effects often focus on intramolecular interactions Steric hindrance is often exploited to control selectivity such as slowing unwanted side reactions Steric hindrance between adjacent groups can also affect torsional bond angles Steric hindrance is responsible for the observed shape of rotaxanes and the low rates of racemization of 2 2 disubstituted biphenyl and binaphthyl derivatives Measures of steric properties editBecause steric effects have profound impact on properties the steric properties of substituents have been assessed by numerous methods Rate data edit Relative rates of chemical reactions provide useful insights into the effects of the steric bulk of substituents Under standard conditions methyl bromide solvolyzes 107 faster than does neopentyl bromide The difference reflects the inhibition of attack on the compound with the sterically bulky CH3 3C group 3 A values edit A values provide another measure of the bulk of substituents A values are derived from equilibrium measurements of monosubstituted cyclohexanes 4 5 6 7 The extent that a substituent favors the equatorial position gives a measure of its bulk nbsp The A value for a methyl group is 1 74 as derived from the chemical equilibrium above It costs 1 74 kcal mol for the methyl group to adopt to the axial position compared to the equatorial position Substituent A Value H 0 CH3 1 74 CH2CH3 1 75 CH CH3 2 2 15 C CH3 3 gt 4 Ceiling temperatures edit Ceiling temperature T c displaystyle T c nbsp is a measure of the steric properties of the monomers that comprise a polymer T c displaystyle T c nbsp is the temperature where the rate of polymerization and depolymerization are equal Sterically hindered monomers give polymers with low T c displaystyle T c nbsp s which are usually not useful Monomer Ceiling temperature C 8 Structure ethylene 610 CH2 CH2 isobutylene 175 CH2 CMe2 1 3 butadiene 585 CH2 CHCH CH2 isoprene 466 CH2 C Me CH CH2 styrene 395 PhCH CH2 a methylstyrene 66 PhC Me CH2 Cone angles edit nbsp Ligand cone angle Ligand cone angles are measures of the size of ligands in coordination chemistry It is defined as the solid angle formed with the metal at the vertex and the hydrogen atoms at the perimeter of the cone see figure 9 Cone angles of common phosphine ligands Ligand Angle PH3 87 P OCH3 3 107 P CH3 3 118 P CH2CH3 3 132 P C6H5 3 145 P cyclo C6H11 3 179 P t Bu 3 182 P 2 4 6 Me3C6H2 3 212Significance and applications editSteric effects are critical to chemistry biochemistry and pharmacology In organic chemistry steric effects are nearly universal and affect the rates and activation 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 In pharmacology steric effects determine how and at what rate a drug will interact with its target bio molecules Prominent sterically hindered compounds nbsp Tris 2 4 di tert butylphenyl phosphite a widely used stabilizer in polymers nbsp Tricyclohexylphosphine a bulky phosphine ligand used in homogeneous catalysis and with B C6F5 3 comprises the classic frustrated Lewis pair 10 nbsp 2 6 Di tert butylphenol is used industrially as UV stabilizers and antioxidants for hydrocarbon based products ranging from petrochemicals to plastics 11 nbsp Hindered amine light stabilizers are widely used in polymers 12 13 nbsp Titanium isopropoxide is a monomer the corresponding titanium ethoxide is a tetramer nbsp An isolable selenenic acid owing to steric protection 14 nbsp The steric effect of tri tert butyl amine makes electrophilic reactions like forming the tetraalkylammonium cation difficult It is difficult for electrophiles to get close enough to allow attack by the lone pair of the nitrogen nitrogen is shown in blue See also editCollision theory Intramolecular force Sterically induced reduction Reaction rate accelerate as result of steric hindrance in the Thorpe Ingold effect Van der Waals strain also known as steric strainReferences edit Gunther Maier Stephan Pfriem Ulrich Schafer Rudolf Matusch 1978 Tetra tert butyltetrahedrane Angew Chem Int Ed Engl 17 7 520 1 doi 10 1002 anie 197805201 Gait Michael 1984 Oligonucleotide synthesis a practical approach Oxford IRL Press ISBN 0 904147 74 6 Smith Michael B March Jerry 2007 Advanced Organic Chemistry Reactions Mechanisms and Structure 6th ed New York Wiley Interscience ISBN 978 0 471 72091 1 E L Eliel S H Wilen and L N Mander Stereochemistry of Organic Compounds Wiley New York 1994 ISBN 81 224 0570 3 Eliel E L Allinger N L Angyal S J G A Morrison 1965 Conformational Analysis New York Interscience Publishers Hirsch J A 1967 Topics in Stereochemistry first ed New York John Wiley amp Sons Inc p 199 Romers C Altona C Buys H R Havinga E 1969 Topics in Stereochemistry fourth ed New York John Wiley amp Sons Inc p 40 Stevens Malcolm P 1999 6 Polymer Chemistry an Introduction 3rd ed New York Oxford University Press pp 193 194 ISBN 978 0 19 512444 6 Tolman Chadwick A 1970 05 01 Phosphorus ligand exchange equilibriums on zerovalent nickel Dominant role for steric effects J Am Chem Soc 92 10 2956 2965 doi 10 1021 ja00713a007 Stephan Douglas W Frustrated Lewis pairs a concept for new reactivity and catalysis Org Biomol Chem 2008 6 1535 1539 doi 10 1039 b802575b Helmut Fiege Heinz Werner Voges Toshikazu Hamamoto Sumio Umemura Tadao Iwata Hisaya Miki Yasuhiro Fujita Hans Josef Buysch Dorothea Garbe Wilfried Paulus 2002 Phenol Derivatives Ullmann s Encyclopedia of Industrial Chemistry Weinheim Wiley VCH pp a19 313 doi 10 1002 14356007 a19 313 ISBN 3 527 30673 0 Pieter Gijsman 2010 Photostabilisation of Polymer Materials In Norman S Allen ed Photochemistry and Photophysics of Polymer Materials Photochemistry Hoboken John Wiley amp Sons pp 627 679 doi 10 1002 9780470594179 ch17 ISBN 978 0 470 59417 9 Klaus Kohler Peter Simmendinger Wolfgang Roelle Wilfried Scholz Andreas Valet Mario Slongo 2010 Paints and Coatings 4 Pigments Extenders and Additives Ullmann s Encyclopedia Of Industrial Chemistry pp o18 o03 doi 10 1002 14356007 o18 o03 ISBN 978 3 527 30673 2 Goto Kei Nagahama Michiko Mizushima Tadashi Shimada Keiichi Kawashima Takayuki Okazaki Renji 2001 The First Direct Oxidative Conversion of a Selenol to a Stable Selenenic Acid Experimental Demonstration of Three Processes Included in the Catalytic Cycle of Glutathione Peroxidase Organic Letters 3 22 3569 3572 doi 10 1021 ol016682s PMID 11678710 External links editSteric Effects chem swin edu au at the Wayback Machine archived July 25 2008 Steric A Program to Calculate the Steric Size of Molecules gh wits ac za at the Wayback Machine archived December 22 2017 Retrieved from https en wikipedia org w index php title Steric effects amp oldid 1224855863 Steric hindrance, wikipedia, wiki, book, books, library,
