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Sigma complexes are of great mechanistic significance, despite their frequent fragility. They represent an initial interaction between the metal center and a hydrocarbon substrate. As such, sigma complexes are generally assumed to be intermediates prior to full oxidative addition .
In chemistry, sigma bonds (σ bonds) or sigma overlap are the strongest type of covalent chemical bond. [1] They are formed by head-on overlapping between atomic orbitals along the internuclear axis. Sigma bonding is most simply defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is ...
In chemistry, sigma hole interactions (or σ-hole interactions) are a family of intermolecular forces that can occur between several classes of molecules and arise from an energetically stabilizing interaction between a positively-charged site, termed a sigma hole, and a negatively-charged site, typically a lone pair, on different atoms that are not covalently bonded to each other. [1]
It is a special case of a C–H sigma complex. Historically, agostic complexes were the first examples of C–H sigma complexes to be observed spectroscopically and crystallographically, due to intramolecular interactions being particularly favorable and more often leading to robust complexes.
Erich Hückel proposed a representation of the double bond as a combination of a sigma bond plus a pi bond. [7] [8] [9] The σ-π representation is the better-known one, and it is the one found in most textbooks since the late-20th century.
Sigma meaning (TODAY Illustration) Lindsay added, “So they have the ‘alpha’ which is the most successful, the best looking and then they have ‘sigma’ which is the same thing as an alpha ...
Psychology Today is an American media organization with a focus on psychology and human behavior. The publication began as a bimonthly magazine, which first appeared in 1967. The print magazine's reported circulation is 275,000 as of 2023. [ 2 ]
Sigma is the Sigma-Aldrich's main biochemical supplier, with offerings including antibiotics, buffers, carbohydrates, enzymes, forensic tools, hematology and histology, nucleotides, proteins, peptides, amino acids and their derivatives.