See also: intramolecular forces

The steric effect of tri-(tert-butyl)amine makes electrophilic reactions, like forming the tetraalkylammonium cation, difficult. An intramolecular force is any force that holds together the atoms making up a molecule or compound In Organic chemistry, butyl is a four- Carbon Alkyl substituent with Chemical formula -C4H9. Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. In Chemistry, an electrophile (literally electron-lover) is a Reagent attracted to Electrons that participates in a chemical reaction by accepting An alkyl is a Univalent radical consisting of Carbon and Hydrogen atoms arranged in a chain Ammonium is also an old name for the Siwa Oasis in western Egypt. It is difficult for electrophiles to get close and attack the lone pair of the nitrogen (nitrogen is shown in blue)

Steric effects arise from the fact that each atom within a molecule occupies a certain amount of space. lone pair is a (valence electron pair without bonding or sharing with other Atoms They are found in the outermost Electron shell of an atom so lone pairs History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by 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. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Electron cloud is a term used if not originally coined by the Nobel Prize laureate and acclaimed educator Richard Feynman in The Feynman Lectures on Physics Max Born (11 December 1882 &ndash 5 January 1970 was a German Physicist and Mathematician who was instrumental in the development of Quantum In Chemistry, conformational isomerism is a form of Stereoisomerism in which Molecules with the same Structural formula (same connectivity A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called

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. Molecular geometry or molecular structure is the three- Dimensional arrangement of the Atoms that constitute a Molecule. 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. Hyperconjugation in Organic chemistry is the stabilizing interaction that results from the interaction of the Electrons in a Sigma bond (usually C-H or A staggered conformation is a Chemical conformation that exists in any open chain single Chemical bond connecting two sp3 hybridised atoms as In Chemistry, conformational isomerism is a form of Stereoisomerism in which Molecules with the same Structural formula (same connectivity ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 ^{[1] [2]}.

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). Hydroxyl in Chemistry stands for a molecule consisting of an Oxygen atom and a Hydrogen atom connected by a Covalent bond. Thymidine (more precisely called deoxythymidine; can also be labelled deoxyribosylthymine, and thymine deoxyriboside) is a Chemical compound Triphenylmethane, or triphenyl methane, is the Hydrocarbon with the formula (C6H53CH Ribose (ɹˈaɪbəʊs ɹˈaɪbəɹʊs primarily seen as D-ribose, is an Aldopentose — a Monosaccharide containing five Carbon Pyridine is a Chemical compound with the formula C5[[Hydrogen H5]] N. ^[3]

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). Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Peter Joseph William Debye ( March 24 1884 &ndash November 2 1966) was a Dutch physicist and physical chemist 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. A random coil is a Polymer Conformation where the Monomer subunits are oriented randomly while still being bonded to adjacent A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds

Steric effects vs. Electronic effects

The structure, properties, and reactivity of a molecule is dependent on straight forward bonding interactions including covalent bonds, ionic bonds, hydrogen bonds and lesser forms of bonding. An ionic bond (or electrovalent bond) is a type of Chemical bond that can often form between Metal and Non-metal Ions (or A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen This bonding supplies a basic molecular skeleton that is modified by repulsive forces. These repulsive forces include the steric interactions described above. Basic bonding and steric are at times insufficient to explain many structures, properties, and reactivity. Thus steric effects are often contrasted and complemented by electronic effects implying the influence of effects such as induction, conjunction, orbital symmetry, electrostatic interactions, and spin state. There are more esoteric electronic effects but these are among the most important when considering structure and chemical reactivity.

Significance

Understanding steric effects is critical to chemistry, biochemistry and pharmacology. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as Pharmacology (from Greek grc φάρμακον pharmakon, "drug" and grc -λογία -logia) is the study of how Drugs In chemistry, steric effects are nearly universal and affect the rates and energies of most chemical reactions to varying degrees. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called 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. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In pharmacology, steric effects determine how and at what rate a drug will interact with its target bio-molecules. Medication, also referred to as medicine, can be loosely defined as any substance intended for use in the diagnosis cure mitigation treatment or prevention of disease

See also

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

References

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/