Steric effects

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Overview

See also: intramolecular forces

Steric effects arise from the fact that each atom within a molecule occupies a certain amount of space. If atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds (Pauli or Born repulsion), and this may affect the molecule's preferred shape (conformation) and reactivity.

There are several types of steric effects:

Steric hindrance or steric resistance occurs when the size of groups within a molecule prevents chemical reactions that are observed in related smaller molecules. Although steric hindrance is sometimes a problem, it can also be a very useful tool, and is often exploited by chemists to change the reactivity pattern of a molecule by stopping unwanted side-reactions (steric protection). Steric hindrance between adjacent groups can also restrict torsional bond angles. However, hyperconjugation has been suggested as an explanation for the preference of the staggered conformation of ethane because the steric hindrance of the small hydrogen atom is far too small. .

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 some cases, for an atom to interact with sterically shielded atoms, it would have to approach from a vicinity where there is less shielding, thus controlling where and from what direction a molecular interaction can take place.

Steric attraction occurs when molecules have shapes or geometries that are optimized for interaction with one another. In these cases molecules will react with each other most often in specific arrangements.

Chain crossing — A random coil can't change from one conformation to a closely related shape by a small displacement if it would require one polymer chain to pass through another, or through itself.

Understanding steric effects is critical to chemistry, biochemistry and pharmacology. 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. In pharmacology, steric effects determine how and at what rate a drug will interact with its target bio-molecules.

See also

• Collision theory
• Reaction rate acceleration as result of steric hindrance in the Thorpe-Ingold effect

External links

• http://www.chem.swin.edu.au/modules/mod4/qsarwebp4.html
• http://www.gh.wits.ac.za/craig/steric/
• http://jilawww.colorado.edu/pubs/thesis/fair/

Cost Effectiveness of Steric effects

| group5 = Clinical Trials Involving Steric effects | list5 = Ongoing Trials on Steric effects at Clinical Trials.gov • Trial results on Steric effects • Clinical Trials on Steric effects at Google

| group6 = Guidelines / Policies / Government Resources (FDA/CDC) Regarding Steric effects | list6 = US National Guidelines Clearinghouse on Steric effects • NICE Guidance on Steric effects • NHS PRODIGY Guidance • FDA on Steric effects • CDC on Steric effects

| group7 = Textbook Information on Steric effects | list7 = Books and Textbook Information on Steric effects

| group8 = Pharmacology Resources on Steric effects | list8 = AND (Dose)}} Dosing of Steric effects • AND (drug interactions)}} Drug interactions with Steric effects • AND (side effects)}} Side effects of Steric effects • AND (Allergy)}} Allergic reactions to Steric effects • AND (overdose)}} Overdose information on Steric effects • AND (carcinogenicity)}} Carcinogenicity information on Steric effects • AND (pregnancy)}} Steric effects in pregnancy • AND (pharmacokinetics)}} Pharmacokinetics of Steric effects •

| group9 = Genetics, Pharmacogenomics, and Proteinomics of Steric effects | list9 = AND (pharmacogenomics)}} Genetics of Steric effects • AND (pharmacogenomics)}} Pharmacogenomics of Steric effects • AND (proteomics)}} Proteomics of Steric effects

| group10 = Newstories on Steric effects | list10 = Steric effects in the news • Be alerted to news on Steric effects • News trends on Steric effects</small>

| group11 = Commentary on Steric effects | list11 = Blogs on Steric effects

| group12 = Patient Resources on Steric effects | list12 = Patient resources on Steric effects • Discussion groups on Steric effects • Patient Handouts on Steric effects • Directions to Hospitals Treating Steric effects • Risk calculators and risk factors for Steric effects

| group13 = Healthcare Provider Resources on Steric effects | list13 = Symptoms of Steric effects • Causes & Risk Factors for Steric effects • Diagnostic studies for Steric effects • Treatment of Steric effects

| group14 = Continuing Medical Education (CME) Programs on Steric effects | list14 = CME Programs on Steric effects

| group15 = International Resources on Steric effects | list15 = Steric effects en Espanol • Steric effects en Francais

| group16 = Business Resources on Steric effects | list16 = Steric effects in the Marketplace • Patents on Steric effects

| group17 = Informatics Resources on Steric effects | list17 = List of terms related to Steric effects

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