Multiple independent instrumental datasets show that the climate system is warming. The 2011–2020 decade warmed to an average 1.09 °C [0.95–1.20 °C] compared to the pre-industrial baseline (1850–1900). Surface temperatures are rising by about 0.2 °C per decade, with 2020 reaching a temperature of 1.2 °C above the pre-industrial era. Since 1950, the number of cold …

An isomeric transition (IT) is the decay of a nuclear isomer to a lower-energy nuclear state. The actual process has two types (modes): γ (gamma) emission (emission of a high-energy photon), ... Isomeric shift; References External links. Research group which presented initial claims of hafnium nuclear isomer de-excitation control. ...

An extended periodic table theorises about chemical elements beyond those currently known in the periodic table and proven. As of 2022, the element with the highest atomic number known is oganesson (Z = 118), which completes the seventh period (row) in the periodic table.All elements in the eighth period and beyond thus remain purely hypothetical. Elements beyond 118 will be …

Delta (/ ˈ d ɛ l t ə /; uppercase Δ, lowercase δ or ????; Greek: δέλτα, délta, ) is the fourth letter of the Greek alphabet.In the system of Greek numerals it has a value of 4. It was derived from the Phoenician letter dalet ????. Letters that come from delta include Latin D and Cyrillic Д.. A river delta (originally, the delta of the Nile River) is so named because its shape ...

The isomeric pairs previously cited as giving very similar proton nmr spectra are now seen to be distinguished by carbon nmr. In the example on the left below (blue box), cyclohexane and 2,3-dimethyl-2-butene both give a single sharp resonance signal in the proton nmr spectrum (the former at δ 1.43 ppm and the latter at 1.64 ppm).

Scope In Diels–Alder reactions. The Diels–Alder reaction of cyclopentadiene with furan can produce two isomeric products. At room temperature, kinetic reaction control prevails and the less stable endo isomer 2 is the main reaction product. At 81 °C and after long reaction times, the chemical equilibrium can assert itself and the thermodynamically more stable exo isomer 1 is …

Absolute configuration refers to the spatial arrangement of atoms within a chiral molecular entity (or group) and its resultant stereochemical description. Absolute configuration is typically relevant in organic molecules, where carbon is bonded to four different substituents.This type of construction creates two possible enantiomers.Absolute configuration uses a set of rules to …

The Wolff rearrangement is a reaction in organic chemistry in which an α-diazocarbonyl compound is converted into a ketene by loss of dinitrogen with accompanying 1,2-rearrangement.The Wolff rearrangement yields a ketene as an intermediate product, which can undergo nucleophilic attack with weakly acidic nucleophiles such as water, alcohols, and …

Two specific further subcategories of tautomerizations: Annular tautomerism is a type of prototropic tautomerism wherein a proton can occupy two or more positions of the heterocyclic systems found in many drugs, for example, 1H- and 3H-imidazole; 1H-, 2H- and 4H- 1,2,4-triazole; 1H- and 2H- isoindole.; Ring–chain tautomers occur when the movement of the proton is …

In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), typically planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to saturated compounds having single bonds, and other geometric or connective non-cyclic arrangements with the same set of atoms. . Aromatic rings …