Solid acids are acids that do not dissolve in the reaction medium. They are used in heterogeneous catalysts. Most of the acids solid in state are organic acids that includes oxalic acid,tartaric acid,citric acid,maleic acid,etc Examples include oxides, which function as Lewis acids including silico-aluminates, sulfated zirconia. Many transition metal oxides are acidic, including titania and niobia; such acids are used in cracking. Many solid Brønsted acids are employed industrially, including sulfonated polystyrene, solid phosphoric acid, niobic acid, heteropolyoxometallates. Solid acids are used in catalysis in many industrial chemical processes, from large-scale catalytic cracking in petroleum refining to the synthesis of various fine chemicals. One large scale application is alkylation, e.g. the combination of benzene and ethylene to give ethylbenzene. Another application is the rearrangement of cyclohexanone oxime to caprolactam. Many alkylamines are prepared by amination of alcohols, catalyzed by solid acids.
Solid acids can be used as electrolytes in fuel cells
Stoichiometry is the calculation of reactants and products in chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products form a ratio of positive integers; this means that if the amounts of the separate reactants are known the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined the amount of the other reactants can be calculated; this is illustrated in the image here, where the balanced equation is: CH4 + 2 O2 → CO2 + 2 H2O. Here, one molecule of methane reacts with two molecules of oxygen gas to yield one molecule of carbon dioxide and two molecules of water; this particular chemical equation is an example of complete combustion. Stoichiometry measures these quantitative relationships, is used to determine the amount of products and reactants that are produced or needed in a given reaction.
Describing the quantitative relationships among substances as they participate in chemical reactions is known as reaction stoichiometry. In the example above, reaction stoichiometry measures the relationship between the methane and oxygen as they react to form carbon dioxide and water; because of the well known relationship of moles to atomic weights, the ratios that are arrived at by stoichiometry can be used to determine quantities by weight in a reaction described by a balanced equation. This is called composition stoichiometry. Gas stoichiometry deals with reactions involving gases, where the gases are at a known temperature and volume and can be assumed to be ideal gases. For gases, the volume ratio is ideally the same by the ideal gas law, but the mass ratio of a single reaction has to be calculated from the molecular masses of the reactants and products. In practice, due to the existence of isotopes, molar masses are used instead when calculating the mass ratio; the term stoichiometry was first used by Jeremias Benjamin Richter in 1792 when the first volume of Richter's Stoichiometry or the Art of Measuring the Chemical Elements was published.
The term is derived from the Ancient Greek words στοιχεῖον stoicheion "element" and μέτρον metron "measure". In patristic Greek, the word Stoichiometria was used by Nicephorus to refer to the number of line counts of the canonical New Testament and some of the Apocrypha. A stoichiometric amount or stoichiometric ratio of a reagent is the optimum amount or ratio where, assuming that the reaction proceeds to completion: All of the reagent is consumed There is no deficiency of the reagent There is no excess of the reagent. Stoichiometry rests upon the basic laws that help to understand it better, i.e. law of conservation of mass, the law of definite proportions, the law of multiple proportions and the law of reciprocal proportions. In general, chemical reactions combine in definite ratios of chemicals. Since chemical reactions can neither create nor destroy matter, nor transmute one element into another, the amount of each element must be the same throughout the overall reaction. For example, the number of atoms of a given element X on the reactant side must equal the number of atoms of that element on the product side, whether or not all of those atoms are involved in a reaction.
Chemical reactions, as macroscopic unit operations, consist of a large number of elementary reactions, where a single molecule reacts with another molecule. As the reacting molecules consist of a definite set of atoms in an integer ratio, the ratio between reactants in a complete reaction is in integer ratio. A reaction may consume more than one molecule, the stoichiometric number counts this number, defined as positive for products and negative for reactants. Different elements have a different atomic mass, as collections of single atoms, molecules have a definite molar mass, measured with the unit mole. By definition, carbon-12 has a molar mass of 12 g/mol. Thus, to calculate the stoichiometry by mass, the number of molecules required for each reactant is expressed in moles and multiplied by the molar mass of each to give the mass of each reactant per mole of reaction; the mass ratios can be calculated by dividing each by the total in the whole reaction. Elements in their natural state are mixtures of isotopes of differing mass, thus atomic masses and thus molar masses are not integers.
For instance, instead of an exact 14:3 proportion, 17.04 kg of ammonia consists of 14.01 kg of nitrogen and 3 × 1.01 kg of hydrogen, because natural nitrogen includes a small amount of nitrogen-15, natural hydrogen includes hydrogen-2. A stoichiometric reactant is a reactant, consumed in a reaction, as opposed to a catalytic reactant, not consumed in the overall reaction because it reacts in one step and is regenerated in another step. Stoichiometry is not only used to balance chemical equations but used in conversions, i.e. converting from grams to moles using molar mass as the conversion factor, or from grams to milliliters using density. For example, to find the amount of NaCl in 2.00 g, one would do the following: 2.00 g NaCl 58.44 g NaCl mol − 1 = 0.034 mol In the above example, when written out in fraction form, the units of grams form a multiplicative identity, equivalent to one, wit
Potassium hydroxide is an inorganic compound with the formula KOH, is called caustic potash. Along with sodium hydroxide, this colorless solid is a prototypical strong base, it has many industrial and niche applications, most of which exploit its caustic nature and its reactivity toward acids. An estimated 700,000 to 800,000 tonnes were produced in 2005. About 100 times more NaOH than KOH is produced annually. KOH is noteworthy as the precursor to most soft and liquid soaps, as well as numerous potassium-containing chemicals, it is a white solid, dangerously corrosive. Most commercial samples are ca. the remainder being water and carbonates. Potassium hydroxide is sold as translucent pellets, which become tacky in air because KOH is hygroscopic. KOH contains varying amounts of water, its dissolution in water is exothermic. Concentrated aqueous solutions are sometimes called potassium lyes. At high temperatures, solid KOH does not dehydrate readily. At higher temperatures, solid KOH crystallizes in the NaCl crystal structure.
The OH group is either or randomly disordered so that the OH− group is a spherical anion of radius 1.53 Å. At room temperature, the OH− groups are ordered and the environment about the K+ centers is distorted, with K+—OH− distances ranging from 2.69 to 3.15 Å, depending on the orientation of the OH group. KOH forms a series of crystalline hydrates, namely the monohydrate KOH, the dihydrate KOH · 2H2O and the tetrahydrate KOH · 4H2O. Like NaOH, KOH exhibits high thermal stability; the gaseous species is dimeric. Because of its high stability and low melting point, it is melt-cast as pellets or rods, forms that have low surface area and convenient handling properties. About 121 g of KOH dissolve in 100 mL water at room temperature, which contrasts with 100 g/100 mL for NaOH, thus on a molar basis, KOH is less soluble than NaOH. Lower molecular-weight alcohols such as methanol and propanols are excellent solvents, they participate in an acid-base equilibrium. In the case of methanol the potassium methoxide forms: KOH + СН3ОН ↽ − ⇀ СН3ОК + H2OBecause of its high affinity for water, KOH serves as a desiccant in the laboratory.
It is used to dry basic solvents amines and pyridines. KOH, like NaOH, serves as a source of OH−, a nucleophilic anion that attacks polar bonds in both inorganic and organic materials. Aqueous KOH saponifies esters: KOH + RCOOR' → RCOOK + R'OHWhen R is a long chain, the product is called a potassium soap; this reaction is manifested by the "greasy" feel that KOH gives when touched — fats on the skin are converted to soap and glycerol. Molten KOH is used to displace other leaving groups; the reaction is useful for aromatic reagents to give the corresponding phenols. Complementary to its reactivity toward acids, KOH attacks oxides. Thus, SiO2 is attacked by KOH to give soluble potassium silicates. KOH reacts with carbon dioxide to give bicarbonate: KOH + CO2 → KHCO3 Historically, KOH was made by adding potassium carbonate to a strong solution of calcium hydroxide The salt metathesis reaction results in precipitation of solid calcium carbonate, leaving potassium hydroxide in solution: Ca2 + K2CO3 → CaCO3 + 2 KOHFiltering off the precipitated calcium carbonate and boiling down the solution gives potassium hydroxide.
This method of producing potassium hydroxide remained dominant until the late 19th century, when it was replaced by the current method of electrolysis of potassium chloride solutions. The method is analogous to the manufacture of sodium hydroxide: 2 KCl + 2 H2O → 2 KOH + Cl2 + H2Hydrogen gas forms as a byproduct on the cathode. Separation of the anodic and cathodic spaces in the electrolysis cell is essential for this process. KOH and NaOH can be used interchangeably for a number of applications, although in industry, NaOH is preferred because of its lower cost. Many potassium salts are prepared by neutralization reactions involving KOH; the potassium salts of carbonate, permanganate and various silicates are prepared by treating either the oxides or the acids with KOH. The high solubility of potassium phosphate is desirable in fertilizers; the saponification of fats with KOH is used to prepare the corresponding "potassium soaps", which are softer than the more common sodium hydroxide-derived soaps.
Because of their softness and greater solubility, potassium soaps require less water to liquefy, can thus contain more cleaning agent than liquefied sodium soaps. Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium, nickel-hydrogen, manganese dioxide-zinc. Potassium hydroxide is preferred over sodium hydroxide; the nickel–metal hydride batteries in the Toyota Prius use a mixture of potassium hydroxide and sodium hydroxide. Nickel–iron batteries use potassium hydroxide electrolyte. In food products, potassium hydroxide acts as a food thickener, pH control agent and food stabilizer; the FDA considers it as safe when combined with "good" manufacturing practice conditions of use. It is known in the E number system as E525. Like sodium hydroxide, potassium hydroxide attracts numerous specialized applications all of which rely on its properties as a strong chemical base with its consequent abili
Chiral Lewis acid
Chiral Lewis acids are a type of Lewis acid catalyst that effects the chirality of the substrate as it reacts with it. In such reactions the synthesis favors the formation of a specific diastereomer; the method is an enantioselective asymmetric synthesis reaction. Since they affect chirality, they produce optically active products from optically inactive or mixed starting materials; this type of preferential formation of one enantiomer or diastereomer over the other is formally known as an asymmetric induction. In this kind of Lewis acid; the electron-accepting atom is a metal, such as indium, lithium, titanium, or boron. The chiral-altering ligands employed for synthesizing these acids most have multiple Lewis basic sites that allow the formation of a ring structure involving the metal atom. Achiral Lewis acids have been used for decades to promote the synthesis of racemic mixtures in a myriad different reactions. Starting in the 1960s chemists have use the chiral acids to induce the enantioselective reactions.
Common reaction types include Diels-Alder reactions, the ene reaction, cycloaddition reactions, hydrocyanation of aldehydes, most notably, Sharpless expoxidations. The enantioselectivity of CLAs derives from their ability to perturb the free energy barrier along the reaction coordinate pathway that leads to either the R- or S- enantiomer. Ground state diastereomers and enantiomers are of equal energy in the ground state, when reacted with an achiral lewis acid, their diastereomeric intermediates, transition states, products are of equal energy; this leads to the production of racemic mixtures of products. However, when a CLA is used in the same reaction, the energetic barrier of formation of one diastereomer is less than that of another – the reaction is under kinetic control. If the difference in the energy barriers between the diastereomeric transition states are of sufficient magnitude a high enantiomeric excess of one isomer should be observed. Diels-Alder reactions occur between an alkene.
This cycloaddition process allows for the stereoselective formation of cyclohexene rings capable of possessing as many as four contiguous stereogenic centers. Diels-Alder reactions can lead to formation of a variety of structural stereoisomers; the molecular orbital theory considers that endo transition state, instead of the exo transition state, is favored. Augmented secondary orbital interactions have been postulated as the source of enhanced endo diastereoselection; the addition of a CLA selectively activates one component of the reaction while providing a stereodefined environment that permits unique enantioselectivity. Koga and coworkers disclosed the first practical example of a catalytic enantioselective Diels-Alder reaction promoted by a CLA - menthoxyaluminum dichloride - derived from menthol and ethylaluminum dichloride. A decade Elias James Corey introduced an effective aluminum-diamine controller for Diels-Alder reaction. Formation of the active catalyst is achieved by treatment of the bis with trimethylaluminum.
The proposed tetracoordinate aluminum prevent the imide acting as a chelating Lewis base, while enhance the α-vinyl proton of the dienphile and the benzylic proton of the catalyst. The X-ray structure of the catalyst showed a stereodefined environment. In 1993, Wulff and coworkers found a complex derived from diethylaluminium chloride and a “vaulted” biaryl ligand below catalyzed the enantioselective Diels-Alder reaction between cyclopentadiene and methacrolein; the chiral ligand is recovered quantitatively by silica gel chromatography. Hisashi Yamamoto and coworkers have developed a practical Diels-Alder catalyst for aldehyde dienophiles; the chiral borane complex is effective in catalyzing a number of aldehyde Diels-Alder reactions. NMR spectroscopic experiments indicated close proximity of the aryl ring. Pi stacking between the aryl group and aldehyde was suggested as an organizational feature which imparted high enantioselectivity to the cycloaddition. Yamamoto and co-wokers have introduced a conceptually interesting series of catalysts that incorporate an acidic proton into the active catalyst.
This kind of what so called Bronsted acid-assisted chiral Lewis acid catalyzes a number of diene-aldehyde cycloaddition reactions. In the aldol reaction, the diastereoselectivity of the product is dictated by the geometry of the enolate according to the Zimmerman-Traxler model; the model predicts that the Z enolate will give syn products and that E enolates will give anti products. Chiral Lewis acids allow products that defy the Zimmerman-Traxler model, allows for control of absolute stereochemistry. Kobayashi and Horibe demonstrated this in the synthesis of dihydroxythioester derivatives, using a tin-based chiral Lewis acid; the transition structures for reactions with both the R and S catalyst enantiomers are shown below. The Baylis-Hillman reaction is a route for C-C bond formation between an alpha, beta-unsaturated carbonyl and an aldehyde, which requires a nucleophilic catalyst a tertiary amine, for a Michael-type addition and elimination; the stereoselectivity of these reactions is poor.
Chen et al. demonstrated an enantioselective chiral Lewis acid-catalyzed reaction. Lanthanum was used in this case. A chiral amine may be used to achieve stereoselectivity; the product obtained by the reaction using the chiral catalyst was obtained in good yield with excellent enantioselectivity. Chiral lewis acids have proven useful in the ene reaction. When
Calcium hydroxide is an inorganic compound with the chemical formula Ca2. It is a colorless crystal or white powder and is obtained when quicklime is mixed, or slaked with water, it has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater is the common name for a saturated solution of calcium hydroxide. Calcium hydroxide is insoluble in water, with a solubility product Ksp of 5.5 × 10−6. It is large enough that its solutions are basic according to the following reaction: Ca2 → Ca2+ + 2 OH−At ambient temperature. Calcium hydroxide dissolves in pure water to produce an alkaline solution with a pH of about 12.4. Calcium hydroxide solutions can cause chemical burns. At high pH value, its solubility drastically decreases; this behavior is relevant to cement pastes. Aqueous solutions of calcium hydroxide are called limewater and are medium strength bases that reacts with acids and can attack some metals such as aluminium while protecting other metals from corrosion such as iron and steel by passivation of their surface.
Limewater turns milky in the presence of carbon dioxide due to formation of calcium carbonate, a process called carbonatation:for example lime water Ca2 + CO2 → CaCO3 + H2OWhen heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa, which decomposes calcium hydroxide into calcium oxide and water. Ca2 → CaO + H2O Calcium hydroxide adopts a polymeric structure; the structure is identical to that of Mg2. Strong hydrogen bonds exist between the layers. Calcium hydroxide is produced commercially by treating lime with water: CaO + H2O → Ca2In the laboratory it can be prepared by mixing aqueous solutions of calcium chloride and sodium hydroxide; the mineral form, portlandite, is rare but can be found in some volcanic and metamorphic rocks. It has been known to arise in burning coal dumps; the positively charged. The solubility of calcium hydroxide at 70 °C is about half of its value at 25 °C; the reason for this rather uncommon phenomenon is that the dissolution of calcium hydroxide in water is an exothermic process, adheres to Le Chatelier's principle.
A lowering of temperature thus favours the elimination of the heat liberated through the process of dissolution and increases the equilibrium constant of dissolution of Ca2, so increase its solubility at low temperature. This counter-intuitive temperature dependence of the solubility is referred to as "retrograde" or "inverse" solubility; the variably hydrated phases of calcium sulfate exhibit a retrograde solubility for the same reason because their dissolution reactions are exothermic. One significant application of calcium hydroxide is in water and sewage treatment, it forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product. This application is enabled by the low cost and low toxicity of calcium hydroxide, it is used in fresh water treatment for raising the pH of the water so that pipes will not corrode where the base water is acidic, because it is self-regulating and does not raise the pH too much. It is used in the preparation of ammonia gas, using the following reaction: Ca2 + 2NH4Cl → 2NH3 + CaCl2 + 2H2OAnother large application is in the paper industry, where it is an intermediate in the reaction in the production of sodium hydroxide.
This conversion is part of the causticizing step in the Kraft process for making pulp. In the causticizing operation, burned lime is added to green liquor, a solution of sodium carbonate and sodium sulfate produced by dissolving smelt, the molten form of these chemicals from the recovery furnace; because of its low toxicity and the mildness of its basic properties, slaked lime is used in the food industry to: clarify raw juice from sugarcane or sugar beets in the sugar industry, process water for alcoholic beverages and soft drinks pickle cucumbers and other foods make Chinese century eggs in maize preparation: removes the cellulose hull of maize kernels clear a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmaceutical uses fortify fruit drinks, such as orange juice, infant formula aid digestion substitute for baking soda in making papadam. Remove carbon dioxide from controlled atmosphere produce storage rooms. In Spanish, calcium hydroxide is called cal.
Maize cooked with cal becomes hominy, which increases the bioavailability of niacin, it is considered tastier and easier to digest. In chewing coca leaves, calcium hydroxide is chewed alongside to keep the alkaloid stimulants chemically available for absorption by the body. Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt mollusc shells to enhance the effects, it has been used by some indigenous American tribes as an ingredient in yopo, a psychedelic snuff prepared from the beans of some Anadenanthera species. Calcium hydroxide is added to a bundle of areca nut and
An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of an O2 -- atom. Metal oxides thus contain an anion of oxygen in the oxidation state of −2. Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide. Materials considered pure elements develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further corrosion. Individual elements can form multiple oxides, each containing different amounts of the element and oxygen. In some cases these are distinguished by specifying the number of atoms as in carbon monoxide and carbon dioxide, in other cases by specifying the element's oxidation number, as in iron oxide and iron oxide. Certain elements can form many different oxides, such as those of nitrogen.
Due to its electronegativity, oxygen forms stable chemical bonds with all elements to give the corresponding oxides. Noble metals are prized because they resist direct chemical combination with oxygen, substances like gold oxide must be generated by indirect routes. Two independent pathways for corrosion of elements are oxidation by oxygen; the combination of water and oxygen is more corrosive. All elements burn in an atmosphere of oxygen or an oxygen-rich environment. In the presence of water and oxygen, some elements— sodium—react to give the hydroxides. In part, for this reason and alkaline earth metals are not found in nature in their metallic, i.e. native, form. Cesium is so reactive with oxygen that it is used as a getter in vacuum tubes, solutions of potassium and sodium, so-called NaK are used to deoxygenate and dehydrate some organic solvents; the surface of most metals consists of hydroxides in the presence of air. A well-known example is aluminium foil, coated with a thin film of aluminium oxide that passivates the metal, slowing further corrosion.
The aluminum oxide layer can be built to greater thickness by the process of electrolytic anodizing. Though solid magnesium and aluminum react with oxygen at STP—they, like most metals, burn in air, generating high temperatures. Finely grained powders of most metals can be dangerously explosive in air, they are used in solid-fuel rockets. In dry oxygen, iron forms iron oxide, but the formation of the hydrated ferric oxides, Fe2O3−x2x, that comprise rust requires oxygen and water. Free oxygen production by photosynthetic bacteria some 3.5 billion years ago precipitated iron out of solution in the oceans as Fe2O3 in the economically important iron ore hematite. Oxides have a range of different structures, from individual molecules to polymeric and crystalline structures. At standard conditions, oxides may range from solids to gases. Oxides of most metals adopt polymeric structures; the oxide links three metal atoms or six metal atoms. Because the M-O bonds are strong and these compounds are crosslinked polymers, the solids tend to be insoluble in solvents, though they are attacked by acids and bases.
The formulas are deceptively simple. Many are nonstoichiometric compounds; some important gaseous oxides. Examples of molecular oxides are carbon monoxide. All simple oxides of nitrogen are molecular, e.g. NO, N2O, NO2 and N2O4. Phosphorus pentoxide is a more complex molecular oxide with a deceptive name, the real formula being P4O10; some polymeric oxides depolymerize when heated to give molecules, examples being selenium dioxide and sulfur trioxide. Tetroxides are rare; the more common examples: ruthenium tetroxide, osmium tetroxide, xenon tetroxide. Many oxyanions are known, such as polyoxometalates. Oxycations are rarer, some examples being nitrosonium and uranyl. Of course many compounds are known with other groups. In organic chemistry, these include many related carbonyl compounds. For the transition metals, many oxo complexes are known as well as oxyhalides. Conversion of a metal oxide to the metal is called reduction; the reduction can be induced by many reagents. Many metal oxides convert to metals by heating.
Metals are "won" from their oxides by chemical reduction, i.e. by the addition of a chemical reagent. A common and cheap reducing agent is carbon in the form of coke; the most prominent example is that of iron ore smelting. Many reactions are involved, but the simplified equation is shown as: 2 Fe2O3 + 3 C → 4 Fe + 3 CO2Metal oxides can be reduced by organic compounds; this redox process is the basis for many important transformations in chemistry, such as the detoxification of drugs by the P450 enzymes and the production of ethylene oxide, converted to antifreeze. In such systems, the metal center transfers an oxide ligand to the organic compound followed by regeneration of the metal oxide by oxygen in the air. Metals that are lower in the reactivity series can be reduced by heating alone. For example, silver oxide decomposes at 200 °C: 2 Ag2O → 4 Ag + O2 Metals that are more reactive displace the oxide of the metals that are less reactive. For example, zinc is more reactive than copper, so it displaces copper oxide to form zinc oxide: Zn + CuO → ZnO + Cu Apart from metals, hydrogen can displace metal oxides to form hydrogen oxide
In chemistry in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, either saturated or unsaturated. Most occurring fatty acids have an unbranched chain of an number of carbon atoms, from 4 to 28. Fatty acids are not found in organisms, but instead as three main classes of esters: triglycerides and cholesterol esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells; the concept of fatty acid was introduced by Michel Eugène Chevreul, though he used some variant terms: graisse acide and acide huileux. Fatty acids differ by length categorized as short to long. Short-chain fatty acids are fatty acids with aliphatic tails of five or fewer carbons. Medium-chain fatty acids are fatty acids with aliphatic tails of 6 to 12 carbons, which can form medium-chain triglycerides. Long-chain fatty acids are fatty acids with aliphatic tails of 13 to 21 carbons. Long chain fatty acids are fatty acids with aliphatic tails of 22 or more carbons.
Saturated fatty acids have no C=C double bonds. They have the same formula CH3nCOOH, with variations in "n". An important saturated fatty acid is stearic acid, which when neutralized with lye is the most common form of soap. Unsaturated fatty acids have one or more C=C double bonds; the C=C double bonds can give either cis or trans isomers. Cis A cis configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain; the rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has; when a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend. Α-Linolenic acid, with three double bonds, favors a hooked shape.
The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be packed, therefore can affect the melting temperature of the membrane or of the fat. Trans A trans configuration, by contrast, means that the adjacent two hydrogen atoms lie on opposite sides of the chain; as a result, they do not cause the chain to bend much, their shape is similar to straight saturated fatty acids. In most occurring unsaturated fatty acids, each double bond has three n carbon atoms after it, for some n, all are cis bonds. Most fatty acids in the trans configuration are not found in nature and are the result of human processing; the differences in geometry between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, in the construction of biological structures. The position of the carbon atoms in a fatty acid can be indicated from the −COOH end, or from the −CH3 end.
If indicated from the −COOH end the C-1, C-2, C-3, …. Notation is used. If the position is counted from the other, −CH3, end the position is indicated by the ω-n notation; the positions of the double bonds in a fatty acid chain can, therefore, be indicated in two ways, using the C-n or the ω-n notation. Thus, in an 18 carbon fatty acid, a double bond between C-12 and C-13 is reported either as Δ12 if counted from the −COOH end, or as ω-6 if counting from the −CH3 end; the "Δ" is the Greek letter delta. Omega is the last letter in the Greek alphabet, is therefore used to indicate the “last” carbon atom in the fatty acid chain. Since the ω-n notation is used exclusively to indicate the positions of the double bonds close to the −CH3 end in essential fatty acids, there is no necessity for an equivalent “Δ”-like notation - the use of the “ω-n” notation always refers to the position of a double bond. Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids.
The difference is relevant to gluconeogenesis. The following table describes the most common systems of naming fatty acids; when circulating in the plasma are not in their ester, fatty acids are known as non-esterified fatty acids or free fatty acids. FFAs are always bound to a transport protein, such as albumin. Fatty acids are produced industrially by the hydrolysis of triglycerides, with the removal of glycerol. Phospholipids represent another source; some fatty acids are produced synthetically by hydrocarboxylation of alkenes. Template:Says whom? In animals, fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, the mammary glands during lactation. Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids. Pyruvate is decarboxylated to form acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids occurs; this cannot occur directly.
To obtain cytosol