Hemoglobin or haemoglobin, abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates as well as the tissues of some invertebrates. Haemoglobin in the blood carries oxygen from the gills to the rest of the body. There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism. A healthy individual has 12 to 16 grams of haemoglobin in every 100 ml of blood. In mammals, the protein makes up about 96% of the red blood cells' dry content, around 35% of the total content. Haemoglobin has an oxygen-binding capacity of 1.34 mL O2 per gram, which increases the total blood oxygen capacity seventy-fold compared to dissolved oxygen in blood. The mammalian hemoglobin molecule can bind up to four oxygen molecules. Hemoglobin is involved in the transport of other gases: It carries some of the body's respiratory carbon dioxide as carbaminohemoglobin, in which CO2 is bound to the heme protein.
The molecule carries the important regulatory molecule nitric oxide bound to a globin protein thiol group, releasing it at the same time as oxygen. Haemoglobin is found outside red blood cells and their progenitor lines. Other cells that contain haemoglobin include the A9 dopaminergic neurons in the substantia nigra, alveolar cells, retinal pigment epithelium, mesangial cells in the kidney, endometrial cells, cervical cells and vaginal epithelial cells. In these tissues, haemoglobin has a non-oxygen-carrying function as an antioxidant and a regulator of iron metabolism. Haemoglobin and haemoglobin-like molecules are found in many invertebrates and plants. In these organisms, haemoglobins may carry oxygen, or they may act to transport and regulate other small molecules and ions such as carbon dioxide, nitric oxide, hydrogen sulfide and sulfide. A variant of the molecule, called leghaemoglobin, is used to scavenge oxygen away from anaerobic systems, such as the nitrogen-fixing nodules of leguminous plants, before the oxygen can poison the system.
In 1825 J. F. Engelhard discovered that the ratio of iron to protein is identical in the hemoglobins of several species. From the known atomic mass of iron he calculated the molecular mass of hemoglobin to n × 16000, the first determination of a protein's molecular mass; this "hasty conclusion" drew a lot of ridicule at the time from scientists who could not believe that any molecule could be that big. Gilbert Smithson Adair confirmed Engelhard's results in 1925 by measuring the osmotic pressure of hemoglobin solutions; the oxygen-carrying property of hemoglobin was discovered by Hünefeld in 1840. In 1851, German physiologist Otto Funke published a series of articles in which he described growing hemoglobin crystals by successively diluting red blood cells with a solvent such as pure water, alcohol or ether, followed by slow evaporation of the solvent from the resulting protein solution. Hemoglobin's reversible oxygenation was described a few years by Felix Hoppe-Seyler. In 1959, Max Perutz determined the molecular structure of hemoglobin by X-ray crystallography.
This work resulted in his sharing with John Kendrew the 1962 Nobel Prize in Chemistry for their studies of the structures of globular proteins. The role of hemoglobin in the blood was elucidated by French physiologist Claude Bernard; the name hemoglobin is derived from the words heme and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme group. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces; the most common type of hemoglobin in mammals contains four such subunits. Hemoglobin consists of protein subunits, these proteins, in turn, are folded chains of a large number of different amino acids called polypeptides; the amino acid sequence of any polypeptide created by a cell is in turn determined by the stretches of DNA called genes. In all proteins, it is the amino acid sequence that determines the protein's chemical properties and function. There is more than one hemoglobin gene: in humans, hemoglobin A is coded for by the genes, HBA1, HBA2, HBB.
The amino acid sequences of the globin proteins in hemoglobins differ between species. These differences grow with evolutionary distance between species. For example, the most common hemoglobin sequences in humans and chimpanzees are nearly identical, differing by only one amino acid in both the alpha and the beta globin protein chains; these differences grow larger between less related species. Within a species, different variants of hemoglobin always exist, although one sequence is a "most common" one in each species. Mutations in the genes for the hemoglobin protein in a species result in hemoglobin variants. Many of these mutant forms of hemoglobin cause no disease; some of these mutant forms of hemoglobin, cause a group of hereditary diseases termed the hemoglobinopathies. The best known hemoglobinopathy is sickle-cell disease, the first human disease whose mechanism was understood at the molecular level. A separate set of diseases called thalassemias involves underproduction of normal and sometimes abnormal hemoglobins, through problems and mutations in globin gene regulation.
All these diseases produce anemia. Variations in hemoglobin amino acid sequences, as with other proteins, may be adaptive. For example, hemoglobin has been found to adapt in different ways to
The blood–brain barrier is a selective semipermeable border that separates the circulating blood from the brain and extracellular fluid in the central nervous system. The blood–brain barrier is formed by endothelial cells of the capillary wall, astrocyte end-feet ensheathing the capillary, pericytes embedded in the capillary basement membrane; this system allows the passage of water, some gases, lipid-soluble molecules by passive diffusion, as well as the selective transport of molecules such as glucose and amino acids that are crucial to neural function. Specialized structures participating in sensory and secretory integration within neural circuits – the circumventricular organs and choroid plexus – do not have a blood–brain barrier; the blood–brain barrier restricts the passage of pathogens, the diffusion of solutes in the blood, large or hydrophilic molecules into the cerebrospinal fluid, while allowing the diffusion of hydrophobic molecules and small polar molecules. Cells of the barrier transport metabolic products such as glucose across the barrier using specific transport proteins.
The blood–brain barrier results from the selectivity of the tight junctions between endothelial cells in CNS vessels, which restricts the passage of solutes. At the interface between blood and the brain, endothelial cells are stitched together by these tight junctions, which are composed of smaller subunits biochemical dimers, that are transmembrane proteins such as occludin, junctional adhesion molecule, or ESAM, for example; each of these transmembrane proteins is anchored into the endothelial cells by another protein complex that includes ZO-1 and associated proteins. The blood–brain barrier is composed of high-density cells restricting passage of substances from the bloodstream much more than do the endothelial cells in capillaries elsewhere in the body. Astrocyte cell projections called astrocytic feet surround the endothelial cells of the BBB, providing biochemical support to those cells; the BBB is distinct from the quite similar blood–cerebrospinal fluid barrier, a function of the choroidal cells of the choroid plexus, from the blood–retinal barrier, which can be considered a part of the whole realm of such barriers.
Several areas of the human brain are not on the brain side of the BBB. Some examples of this include the circumventricular organs, the roof of the third and fourth ventricles, capillaries in the pineal gland on the roof of the diencephalon and the pineal gland; the pineal gland secretes the hormone melatonin "directly into the systemic circulation", thus melatonin is not affected by the blood–brain barrier. Experiments in the 1920s seemed to show that the blood–brain barrier was still immature in newborns; this was due to an error in methodology. It was shown in experiments with a reduced volume of the injected liquids that the markers under investigation could not pass the BBB, it was reported that those natural substances such as albumin, α-1-fetoprotein or transferrin with elevated plasma concentration in the newborn could not be detected outside of cells in the brain. The transporter P-glycoprotein exists in the embryonal endothelium; the measurement of brain uptake of acetamide, benzyl alcohol, caffeine, phenytoin, ethylene glycol, mannitol, phenobarbital, propylene glycol and urea in ether-anesthetized newborn vs. adult rabbits shows that newborn rabbit and adult rabbit brain endothelia are functionally similar with respect to lipid-mediated permeability.
These data confirmed that no differences in permeability could be detected between newborn and adult BBB capillaries. No difference in brain uptake of glucose, amino acids, organic acids, nucleosides, or choline was observed between adult and newborn rabbits; these experiments indicate that the newborn BBB has restrictive properties similar to that of the adult. In contrast to suggestions of an immature barrier in young animals, these studies indicate that a sophisticated, selective BBB is operative at birth; the blood–brain barrier acts to protect the brain from circulating pathogens. Accordingly, blood-borne infections of the brain are rare. Infections of the brain that do occur are difficult to treat. Antibodies are too large to cross the blood–brain barrier, only certain antibiotics are able to pass. In some cases, a drug has to be administered directly into the cerebrospinal fluid where it can enter the brain by crossing the blood–cerebrospinal fluid barrier; the blood–brain barrier may become leaky in select neurological diseases, such as amyotrophic lateral sclerosis, brain trauma and edema, in systemic diseases, such as liver failure.
The blood–brain barrier becomes more permeable during inflammation, allowing antibiotics and phagocytes to move across the BBB. However, this allows bacteria and viruses to infiltrate the blood–brain barrier. Examples of pathogens that can traverse the blood–brain barrier include Toxoplasma gondii which causes toxoplasmosis, spirochetes like Borrelia, Group B streptococci which causes meningitis in newborns, Treponema pallidum which causes syphilis; some of these harmful bacteria gain access by releasing cytotoxins like pneumolysin which have a direct toxic effect on brain microvascular endothelium and tight junctions. Circumventricular organs are individual structures located adjacent to the fourth ventricle or third ventricle in the brain, are characterized by dense capillary beds with permeable endothelial cells unlike those of the blood–brain barrier. I
Trichloroethyl chloroformate is used in organic synthesis for the introduction of the trichloroethyl chloroformate protecting group for amines and alcohols. It cleaves vs other carbamates and can be used in an overall protecting group strategy; the troc group is traditionally removed via Zn insertion in the presence of acetic acid, resulting in elimination and decarboxylation. 2,2,2-Trichloroethoxycarbonyl group is used as a protecting group for amines in organic synthesis. 2,2,2-Trichloroethyl chloroformate, pyridine or aqueous sodium hydroxide at ambient temperatureElectrolysisDeprotection using zinc metal
Insecticides are substances used to kill insects. They include larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, industry and by consumers. Insecticides are claimed to be a major factor behind the increase in the 20th-century's agricultural productivity. Nearly all insecticides have the potential to alter ecosystems. Insecticides can be classified into two major groups: systemic insecticides, which have residual or long term activity. Furthermore, one can distinguish three types of insecticide. 1. Natural insecticides, such as nicotine and neem extracts, made by plants as defenses against insects. 2. Inorganic insecticides. 3. Organic insecticides, which are organic chemical compounds working by contact; the mode of action describes how the pesticide inactivates a pest. It provides another way of classifying insecticides. Mode of action is important in understanding whether an insecticide will be toxic to unrelated species, such as fish and mammals. Insecticides may be non-repellent.
Social insects such as ants cannot detect non-repellents and crawl through them. As they return to the nest they take transfer it to their nestmates. Over time, this eliminates all of the ants including the queen; this is slower than some other methods, but completely eradicates the ant colony. Insecticides are distinct from non-insecticidal repellents, which do not kill. Systemic insecticides become distributed systemically throughout the whole plant; when insects feed on the plant, they ingest the insecticide. Systemic insecticides produced by transgenic plants are called plant-incorporated protectants. For instance, a gene that codes for a specific Bacillus thuringiensis biocidal protein was introduced into corn and other species; the plant manufactures the protein. Contact insecticides are toxic to insects upon direct contact; these can be inorganic insecticides, which are metals and include the used sulfur, the less used arsenates and fluorine compounds. Contact insecticides can be organic insecticides, i.e. organic chemical compounds, synthetically produced, comprising the largest numbers of pesticides used today.
Or they can be natural compounds like neem oil etc.. Contact insecticides have no residual activity. Efficacy can be related to the quality of pesticide application, with small droplets, such as aerosols improving performance. Many organic compounds are produced by plants for the purpose of defending the host plant from predation. A trivial case is tree rosin, a natural insecticide; the production of oleoresin by conifer species is a component of the defense response against insect attack and fungal pathogen infection. Many fragrances, e.g. oil of wintergreen, are in fact antifeedants. Four extracts of plants are in commercial use: pyrethrum, neem oil, various essential oils Transgenic crops that act as insecticides began in 1996 with a genetically modified potato that produced the Cry protein, derived from the bacterium Bacillus thuringiensis, toxic to beetle larvae such as the Colorado potato beetle; the technique has been expanded to include the use of RNA interference RNAi that fatally silences crucial insect genes.
RNAi evolved as a defense against viruses. Midgut cells in many larvae help spread the signal; the technology can target only insects that have the silenced sequence, as was demonstrated when a particular RNAi affected only one of four fruit fly species. The technique is expected to replace many other insecticides, which are losing effectiveness due to the spread of pesticide resistance. Many plants exude substances to repel insects. Premier examples are substances activated by the enzyme myrosinase; this enzyme converts glucosinolates to various compounds. One product of this enzyme is the pungent ingredient in horseradish sauces; the myrosinase is released only upon crushing the flesh of horseradish. Since allyl isothiocyanate is harmful to the plant as well as the insect, it is stored in the harmless form of the glucosinolate, separate from the myrosinase enzyme. Bacillus thuringiensis is a bacterial disease that affects some other insects. Toxins produced by strains of this bacterium are used as a larvicide against caterpillars and mosquitoes.
Toxins from Saccharopolyspora spinosa are sold as Spinosad. Because these toxins have little effect on other organisms, they are considered more environmentally friendly than synthetic pesticides; the toxin from B. thuringiensis has been incorporated directly into plants through the use of genetic engineering. Other biological insecticides include products based on entomopathogenic fungi and viruses. A major emphasis of organic chemistry is the development of chemical tools to enhance agricultural productivity. Insecticides represent a major area of emphasis. Many of the major insecticides are inspired by biological analogues. Many others are alien to nature; the best known organochloride, DDT, was created by Swiss scientist Paul Müller. For this discovery, he was awarded the 1948 Nobel Prize for Medicine. DDT was introduced in 1944, it functions by opening sodium channels in
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
Glutamic acid is an α-amino acid, used by all living beings in the biosynthesis of proteins. It is non-essential in humans, it is an excitatory neurotransmitter, in fact the most abundant one, in the vertebrate nervous system. It serves as the precursor for the synthesis of the inhibitory gamma-aminobutyric acid in GABA-ergic neurons, it has a formula C5H9O4N. Its molecular structure could be idealized as HOOC-CH-2-COOH, with two carboxyl groups -COOH and one amino group -NH2. However, in the solid state and mildly acid water solutions, the molecule assumes an electrically neutral zwitterion structure −OOC-CH-2-COOH, it is encoded by the codons GAA or GAG. The acid can lose one proton from its second carboxyl group to form the conjugate base, the singly-negative anion glutamate −OOC-CH-2-COO−; this form of the compound is prevalent in neutral solutions. The glutamate neurotransmitter plays the principal role in neural activation; this anion is responsible for the savory flavor of certain foods, used in glutamate flavorings such as MSG.
In Europe it is classified as food additive E620. In alkaline solutions the doubly negative anion −OOC-CH-2-COO− prevails; the radical corresponding to glutamate is called glutamyl. When glutamic acid is dissolved in water, the amino group may gain a proton, and/or the carboxyl groups may lose protons, depending on the acidity of the medium. In sufficiently acidic environments, the amino group gains a proton and the molecule becomes a cation with a single positive charge, HOOC-CH-2-COOH. At pH values between about 2.5 and 4.1, the carboxylic acid closer to the amine loses a proton, the acid becomes the neutral zwitterion −OOC-CH-2-COOH. This is the form of the compound in the crystalline solid state; the change in protonation state is gradual. At higher pH, the other carboxylic acid group loses its proton and the acid exists entirely as the glutamate anion −OOC-CH-2-COO−, with a single negative charge overall; the change in protonation state occurs at pH 4.07. This form with both carboxylates lacking protons is dominant in the physiological pH range.
At higher pH, the amino group loses the extra proton and the prevalent species is the doubly-negative anion −OOC-CH-2-COO−. The change in protonation state occurs at pH 9.47. The carbon atom adjacent to the amino group is chiral, so glutamic acid can exist in two optical isomers, D and L; the L form is the one most occurring in nature, but the D form occurs in some special contexts, such as the cell walls of the bacteria and the liver of mammals. Although they occur in many foods, the flavor contributions made by glutamic acid and other amino acids were only scientifically identified early in the twentieth century; the substance was discovered and identified in the year 1866, by the German chemist Karl Heinrich Ritthausen who treated wheat gluten with sulfuric acid. In 1908 Japanese researcher Kikunae Ikeda of the Tokyo Imperial University identified brown crystals left behind after the evaporation of a large amount of kombu broth as glutamic acid; these crystals, when tasted, reproduced the ineffable but undeniable flavor he detected in many foods, most in seaweed.
Professor Ikeda termed this flavor umami. He patented a method of mass-producing a crystalline salt of glutamic acid, monosodium glutamate. Glutamic acid is produced on the largest scale of any amino acid, with an estimated annual production of about 1.5 million tons in 2006. Chemical synthesis was supplanted by the aerobic fermentation of sugars and ammonia in the 1950s, with the organism Corynebacterium glutamicum being the most used for production. Isolation and purification can be achieved by crystallization. Glutamate is a key compound in cellular metabolism. In humans, dietary proteins are broken down by digestion into amino acids, which serve as metabolic fuel for other functional roles in the body. A key process in amino acid degradation is transamination, in which the amino group of an amino acid is transferred to an α-ketoacid catalysed by a transaminase; the reaction can be generalised as such: R1-amino acid + R2-α-ketoacid ⇌ R1-α-ketoacid + R2-amino acidA common α-keto acid is α-ketoglutarate, an intermediate in the citric acid cycle.
Transamination of α-ketoglutarate gives glutamate. The resulting α-ketoacid product is a useful one as well, which can contribute as fuel or as a substrate for further metabolism processes. Examples are as follows: Alanine + α-ketoglutarate ⇌ pyruvate + glutamateAspartate + α-ketoglutarate ⇌ oxaloacetate + glutamateBoth pyruvate and oxaloacetate are key components of cellular metabolism, contributing as substrates or intermediates in fundamental processes such as glycolysis and the citric acid cycle. Glutamate plays an important role in the body's disposal of excess or waste nitrogen. Glutamate undergoes deamination, an oxidative reaction catalysed by glutamate dehydrogenase, as follows: glutamate + H2O + NADP+ → α-ketoglutarate + NADPH + NH3 + H+Ammonia is excreted predominantly as urea, synthesised in the liver. Transamination can thus be linked to deamination allowing nitrogen from the amine groups of amino acids to be removed, via glutamate as an intermediate, excreted from the body in the form of urea.
Glutamate is a
In chemistry, an alcohol is any organic compound in which the hydroxyl functional group is bound to a carbon. The term alcohol referred to the primary alcohol ethanol, used as a drug and is the main alcohol present in alcoholic beverages. An important class of alcohols, of which methanol and ethanol are the simplest members, includes all compounds for which the general formula is CnH2n+1OH, it is these simple monoalcohols. The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; when a higher priority group is present in the compound, the prefix hydroxy- is used in its IUPAC name. The suffix -ol in non-IUPAC names typically indicates that the substance is an alcohol. However, many substances that contain hydroxyl functional groups have names which include neither the suffix -ol, nor the prefix hydroxy-. Alcohol distillation originated in India. During 2000 BCE, people of India used. Alcohol distillation was known to Islamic chemists as early as the eighth century.
The Arab chemist, al-Kindi, unambiguously described the distillation of wine in a treatise titled as "The Book of the chemistry of Perfume and Distillations". The Persian physician, alchemist and philosopher Rhazes is credited with the discovery of ethanol; the word "alcohol" is from a powder used as an eyeliner. Al- is the Arabic definite article, equivalent to the in English. Alcohol was used for the fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide Sb2S3, it was considered to be the essence or "spirit" of this mineral. It was used as an antiseptic and cosmetic; the meaning of alcohol was extended to distilled substances in general, narrowed to ethanol, when "spirits" was a synonym for hard liquor. Bartholomew Traheron, in his 1543 translation of John of Vigo, introduces the word as a term used by "barbarous" authors for "fine powder." Vigo wrote: "the barbarous auctours use alcohol, or alcofoll, for moost fine poudre."The 1657 Lexicon Chymicum, by William Johnson glosses the word as "antimonium sive stibium."
By extension, the word came to refer to any fluid obtained by distillation, including "alcohol of wine," the distilled essence of wine. Libavius in Alchymia refers to "vini alcohol vel vinum alcalisatum". Johnson glosses alcohol vini as "quando omnis superfluitas vini a vino separatur, ita ut accensum ardeat donec totum consumatur, nihilque fæcum aut phlegmatis in fundo remaneat." The word's meaning became restricted to "spirit of wine" in the 18th century and was extended to the class of substances so-called as "alcohols" in modern chemistry after 1850. The term ethanol was invented 1892, combining the word ethane with the "-ol" ending of "alcohol". IUPAC nomenclature is used in scientific publications and where precise identification of the substance is important in cases where the relative complexity of the molecule does not make such a systematic name unwieldy. In naming simple alcohols, the name of the alkane chain loses the terminal e and adds the suffix -ol, e.g. as in "ethanol" from the alkane chain name "ethane".
When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the -ol: propan-1-ol for CH3CH2CH2OH, propan-2-ol for CH3CHCH3. If a higher priority group is present the prefix hydroxy-is used, e.g. as in 1-hydroxy-2-propanone. In cases where the OH functional group is bonded to an sp2 carbon on an aromatic ring the molecule is known as a phenol, is named using the IUPAC rules for naming phenols. In other less formal contexts, an alcohol is called with the name of the corresponding alkyl group followed by the word "alcohol", e.g. methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane chain; as described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is indicated using the "hydroxy-" prefix. Alcohols are classified into primary and tertiary, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group.
The primary alcohols have general formulas RCH2OH. The simplest primary alcohol is methanol, for which R=H, the next is ethanol, for which R=CH3, the methyl group. Secondary alcohols are those of the form RR'CHOH, the simplest of, 2-propanol. For the tertiary alcohols the general form is RR'R"COH; the simplest example is tert-butanol, for which each of R, R', R" is CH3. In these shorthands, R, R', R" represent substituents, alkyl or other attached organic groups. In archaic nomenclature, alcohols can be named as derivatives of methanol using "-carbinol" as the ending. For instance, 3COH can be named trimethylcarbinol. Alcohols have a long history of myriad uses. For simple mono-alcohols, the focus on this article, the following are most important industrial alcohols: methanol for the production of formaldehyde and as a fuel additive ethanol for alcoholic beverages, fuel additive, solvent 1-propanol, 1-butanol, isobutyl alcohol for use as a solvent a