|
Push–pull Olefin
A push-pull olefin is a type of olefin characterized by an electron-withdrawing substituent on one side of the double bond and an electron-donating substituent on the other side. This makes the pi bond very polarized. The rotational barrier for a push-pull olefin is lower than that of an ordinary olefin and this makes it an interesting candidate for a molecular switch, for instance azobenzenes. A push-pull configuration also helps to stabilize the double bond because the carbon-carbon bond has considerably less double bond character. For instance, cyclobutadiene is a very unstable molecule but with both olefinic bonds in push-pull configuration (two ester substituents and two tertiary amine substituents) the molecule is stable indeed. References * ''Ethyl (2-cyano-3-ethoxyacryloyl)carbamate: irreversible thermal isomerization of a push-pull olefin'' Kuangsen Sung, Ming-Chi Lin, Pin-Mei Huang, Bo-Ren Zhuang, Robert Sung,Ru-Rong Wu Arkivoc 2005 p. 13 open access (publishing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Olefin
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, and Biological Chemistry'. 1232 pages. Two general types of monoalkenes are distinguished: terminal and internal. Also called α-olefins, terminal alkenes are more useful. However, the International Union of Pure and Applied Chemistry (IUPAC) recommends using the name "alkene" only for acyclic hydrocarbons with just one double bond; alkadiene, alkatriene, etc., or polyene for acyclic hydrocarbons with two or more double bonds; cycloalkene, cycloalkadiene, etc. for cyclic ones; and "olefin" for the general class – cyclic or acyclic, with one or more double bonds. Acyclic alkenes, with only one double bond and no other functional groups (also known as mono-enes) form a homologous series of hydrocarbons with the general formula with ''n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclobutadiene
Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is quite stable. Since the compound degrades by a bimolecular process, the species can be observed by matrix isolation techniques at temperatures below 35 K. It is thought to adopt a rectangular structure. Structure and reactivity The compound is the prototypical antiaromatic hydrocarbon with 4 π-electrons. It is the smallest 'n''annulene ( annulene). Its rectangular structure is the result of the Jahn–Teller effect, which distorts the molecule and lowers its symmetry, converting the triplet to a singlet ground state. The electronic states of cyclobutadiene have been explored with a variety of computational methods. The rectangular structure is consistent with the existence of two different 1,2-dideutero-1,3-cyclobutadiene valence iso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Logic Gate
A molecular logic gate is a molecule that performs a logical operation based on one or more physical or chemical inputs and a single output. The field has advanced from simple logic systems based on a single chemical or physical input to molecules capable of combinatorial and sequential operations such as arithmetic operations (i.e. moleculators and memory storage algorithms). For logic gates with a single input, there are four possible output patterns. When the input is 0, the output can be either a 0 or 1. When the input is 1, the output can again be 0 or 1. The four output bit patterns that can arise corresponds to a specific logic type: PASS 0, YES, NOT and PASS 1. PASS 0 always outputs 0, whatever the input. PASS 1 always outputs 1, whatever the input. YES outputs a 1 when the input is 1 and NOT is the inverse YES – it outputs a 0 when the input is 1. An example of a YES logic gate is the molecular structure shown below. A "1" output is given only when sodium ions are presen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leimgruber–Batcho Indole Synthesis
The Leimgruber–Batcho indole synthesis is a series of organic reactions that produce indoles from o-nitrotoluenes 1. The first step is the formation of an enamine 2 using N,N-dimethylformamide dimethyl acetal and pyrrolidine. The desired indole 3 is then formed in a second step by reductive cyclisation. In the above scheme, the reductive cyclisation is effected by Raney nickel and hydrazine. Palladium-on-carbon and hydrogen, stannous chloride, sodium hydrosulfite, or iron in acetic acid are also effective reducing agents. Reaction mechanism In the initial enamine formation, dimethylamine (a gas) is displaced by pyrrolidine from the dimethylformamide dimethylacetal, producing a more reactive reagent. The mildly acidic hydrogens of the methyl group in the nitrotoluene can be deprotonated under the basic conditions, and the resultant carbanion attacks to produce the enamine shown, with loss of methanol. The sequence can also be performed without pyrrolidine, via the N,N ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Open Access (publishing)
Open access (OA) is a set of principles and a range of practices through which research outputs are distributed online, free of access charges or other barriers. With open access strictly defined (according to the 2001 definition), or libre open access, barriers to copying or reuse are also reduced or removed by applying an open license for copyright. The main focus of the open access movement is "peer reviewed research literature". Historically, this has centered mainly on print-based academic journals. Whereas non-open access journals cover publishing costs through access tolls such as subscriptions, site licenses or pay-per-view charges, open-access journals are characterised by funding models which do not require the reader to pay to read the journal's contents, relying instead on author fees or on public funding, subsidies and sponsorships. Open access can be applied to all forms of published research output, including peer-reviewed and non peer-reviewed academic journal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arkivoc
''Arkivoc'' (''Archive for Organic Chemistry'') is a peer-reviewed open access scientific journal covering all aspects of organic chemistry. It is published by the non-profit organization Arkat USA, which was established in 2000 through a personal donation from Alan R. Katritzky and Linde Katritzky. ''Arkivoc'' is the primary publication of Arkat USA. According to the ''Journal Citation Reports'', the journal has a 2014 impact factor The impact factor (IF) or journal impact factor (JIF) of an academic journal is a scientometric index calculated by Clarivate that reflects the yearly mean number of citations of articles published in the last two years in a given journal, as i ... of 1.165, ranking it 37th out of 57 journals in the category "Chemistry, Organic". Abstracting and Indexing According to the Journal Citation Reports, the journal has a 2018 impact factor of 1.253. The journal is indexed in Web of Science: Science Citation Index Expanded. References External link ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tertiary Amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of substituent are attached to one nitrogen atom may be called alkylarylamines). Important amines include amino acids, biogenic amines, trimethylamine, and aniline; Inorganic derivatives of ammonia are also called amines, such as monochloramine (). The substituent is called an amino group. Compounds with a nitrogen atom attached to a carbonyl group, thus having the structure , are called amides and have different chemical properties from amines. Classification of amines Amines can be classified according to the nature and number of substituents on nitrogen. Aliphatic amines contain only H and alkyl substituents. Aromatic a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are fatty acid esters of glycerol; they are important in biology, being one of the main classes of lipids and comprising the bulk of animal fats and vegetable oils. Esters typically have a pleasant smell; those of low molecular weight are commonly used as fragrances and are found in essential oils and pheromones. They perform as high-grade solvents for a broad array of plastics, plasticizers, resins, and lacquers, and are one of the largest classes of synthetic lubricants on the commercial market. Polyesters are important plastics, with monomers linked by ester moieties. Phosphoesters form the backbone of DNA molecules. Nitrate esters, such as nitroglycerin, are known for their explosive properties. '' Nomenclature Etymology Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Azobenzene
Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a N=N double bond. It is the simplest example of an aryl azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of similar compounds. These azo compounds are considered as derivatives of diazene (diimide), and are sometimes referred to as 'diazenes'. The diazenes absorb light strongly and are common dyes. Structure and synthesis ''trans''-Azobenzene is planar. The N-N distance is 1.189 Å. ''cis''-Azobenzene is nonplanar with a C-N=N-C dihedral angle of 173.5°. The N-N distance is 1.251 Å. Azobenzene was first described by Eilhard Mitscherlich in 1834. Yellowish-red crystalline flakes of azobenzene were obtained in 1856. Its original preparation is similar to the modern one. According to the 1856 method, nitrobenzene is reduced by iron filings in the presence of acetic acid. In the modern synthesis, zinc is the reductant in the presence of a base. I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polar Effect
The polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby reaction center. The main contributors to the polar effect are the inductive effect, mesomeric effect and the through-space electronic field effect. An electron-withdrawing group (EWG) draws electrons away from a reaction center. When this center is an electron rich carbanion or an alkoxide anion, the presence of the electron-withdrawing substituent has a stabilizing effect. Examples of electron withdrawing groups are * halogens (F, Cl); * nitriles CN; * carbonyls RCOR'; * nitro groups NO2. An electron-releasing group (ERG) or electron-donating group (EDG) releases electrons into a reaction center and as such stabilizes electron deficient carbocations. Examples of electron releasing groups are * alkyl groups; * alcohol groups; * amino groups. The total substituent effect is the combination of the polar effect and the combined ste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Switch
A molecular switch is a molecule that can be reversibly shifted between two or more stable states. The molecules may be shifted between the states in response to environmental stimuli, such as changes in pH, light, temperature, an electric current, microenvironment, or in the presence of ions and other ligands. In some cases, a combination of stimuli is required. The oldest forms of synthetic molecular switches are pH indicators, which display distinct colors as a function of pH. Currently synthetic molecular switches are of interest in the field of nanotechnology for application in molecular computers or responsive drug delivery systems. Molecular switches are also important in biology because many biological functions are based on it, for instance allosteric regulation and vision. They are also one of the simplest examples of molecular machines. Biological molecular switches In cellular biology, proteins act as intracellular signaling molecules by activating another protein i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rotational Barrier
In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds (refer to figure on single bond rotation). While any two arrangements of atoms in a molecule that differ by rotation about single bonds can be referred to as different conformations, conformations that correspond to local minima on the potential energy surface are specifically called conformational isomers or conformers. Conformations that correspond to local maxima on the energy surface are the transition states between the local-minimum conformational isomers. Rotations about single bonds involve overcoming a rotational energy barrier to interconvert one conformer to another. If the energy barrier is low, there is free rotation and a sample of the compound exists as a rapidly equilibrating mixture of multiple conformers; if the energy barrier is high enough then there is restricted rotation, a molecule may exist for a rel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
