Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio; these spectra are used to determine the elemental or isotopic signature of a sample, the masses of particles and of molecules, to elucidate the chemical structures of molecules and other chemical compounds. In a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons; this may cause some of the sample's molecules to break into charged fragments. These ions are separated according to their mass-to-charge ratio by accelerating them and subjecting them to an electric or magnetic field: ions of the same mass-to-charge ratio will undergo the same amount of deflection.
The ions are detected by a mechanism capable of detecting charged particles, such as an electron multiplier. Results are displayed as spectra of the relative abundance of detected ions as a function of the mass-to-charge ratio; the atoms or molecules in the sample can be identified by correlating known masses to the identified masses or through a characteristic fragmentation pattern. In 1886, Eugen Goldstein observed rays in gas discharges under low pressure that traveled away from the anode and through channels in a perforated cathode, opposite to the direction of negatively charged cathode rays. Goldstein called these positively charged anode rays "Kanalstrahlen". Wilhelm Wien found that strong electric or magnetic fields deflected the canal rays and, in 1899, constructed a device with perpendicular electric and magnetic fields that separated the positive rays according to their charge-to-mass ratio. Wien found. English scientist J. J. Thomson improved on the work of Wien by reducing the pressure to create the mass spectrograph.
The word spectrograph had become part of the international scientific vocabulary by 1884. Early spectrometry devices that measured the mass-to-charge ratio of ions were called mass spectrographs which consisted of instruments that recorded a spectrum of mass values on a photographic plate. A mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen. A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be observed. Once the instrument was properly adjusted, a photographic plate was exposed; the term mass spectroscope continued to be used though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope. The use of the term mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy. Mass spectrometry is abbreviated as mass-spec or as MS. Modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F.
W. Aston in 1918 and 1919 respectively. Sector mass spectrometers known as calutrons were developed by Ernest O. Lawrence and used for separating the isotopes of uranium during the Manhattan Project. Calutron mass spectrometers were used for uranium enrichment at the Oak Ridge, Tennessee Y-12 plant established during World War II. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt and Wolfgang Paul for the development of the ion trap technique in the 1950s and 1960s. In 2002, the Nobel Prize in Chemistry was awarded to John Bennett Fenn for the development of electrospray ionization and Koichi Tanaka for the development of soft laser desorption and their application to the ionization of biological macromolecules proteins. A mass spectrometer consists of three components: an ion source, a mass analyzer, a detector; the ionizer converts a portion of the sample into ions. There is a wide variety of ionization techniques, depending on the phase of the sample and the efficiency of various ionization mechanisms for the unknown species.
An extraction system removes ions from the sample, which are targeted through the mass analyzer and into the detector. The differences in masses of the fragments allows the mass analyzer to sort the ions by their mass-to-charge ratio; the detector measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present. Some detectors give spatial information, e.g. a multichannel plate. The following example describes the operation of a spectrometer mass analyzer, of the sector type. Consider a sample of sodium chloride. In the ion source, the sample is ionized into sodium and chloride ions. Sodium atoms and ions are monoisotopic, with a mass of about 23 u. Chloride atoms and ions come in two isotopes with masses of 35 u and 37 u; the analyzer part of the spectrometer contains electric and magnetic fields, which exert forces on ions traveling through these fields. The speed of a charged particle may be increased or decreased while passing through the electric field, its direction may be altered by the magnetic field.
The magnitude of the deflection of the moving ion's trajectory depends on its mass-to-charge ratio. L
The angstrom or ångström is a unit of length equal to 10−10 m. Its symbol is a letter of the Swedish alphabet; the angstrom is not a part of the SI system of units, but it can be considered part of the metric system. While deprecated by the IBWM and the NIST, the unit is still used in the natural sciences and technology to express sizes of atoms, microscopic biological structures, lengths of chemical bonds, arrangement of atoms in crystals, wavelengths of electromagnetic radiation, dimensions of integrated circuit parts; the atomic radii of phosphorus and chlorine are about 1 angstrom, while that of hydrogen is about 0.5 angstrom. Visible light has wavelengths in the range of 4000–7000 Å; the unit is named after the nineteenth-century Swedish physicist Anders Jonas Ångström. The IBWM and the NIST spell it as ångström; the symbol should always be "Å". The angstrom is used extensively in crystallography, solid-state physics and chemistry as a unit for d-spacings, cell parameters, inter-atomic distances and x-ray wavelengths, as these values are in the 1–10 Å range.
For example, the Inorganic Crystal Structure Database presents all these values using the angstrom. Anders Jonas Ångström was a pioneer in the field of spectroscopy, he is well known for his studies of astrophysics, heat transfer, terrestrial magnetism, the aurora borealis. In 1852, Ångström formulated in Optiska undersökningar, a law of absorption modified somewhat and known as Kirchhoff's law of thermal radiation. In 1868, Ångström created a chart of the spectrum of sunlight, in which he expressed the wavelengths of electromagnetic radiation in the electromagnetic spectrum in multiples of one ten-millionth of a millimetre Because the human eye is sensitive to wavelengths from about 4000 to 7000 Å, that choice of unit supported sufficiently accurate measurements of visible wavelengths without resorting to fractional numbers. Ångström's chart and table of wavelengths in the solar spectrum became used in solar physics, which adopted the unit and named it after him. It subsequently spread to the rest of astronomical spectroscopy, atomic spectroscopy, subsequently to other sciences that deal with atomic-scale structures.
Though intended to correspond to 10−10 metres, for precise spectral analysis, the angstrom had to be defined more than the metre, which until 1960 was still defined based on the length of a bar of metal held in Paris. The use of metal bars had been involved in an early error in the value of the angstrom of about one part in 6000. Ångström took the precaution of having the standard bar he used checked against a standard in Paris, but the metrologist Henri Tresca reported it to be so much shorter than it was that Ångström's corrected results were more in error than the uncorrected ones. In 1892–1895, Albert A. Michelson defined the angstrom so that the red line of cadmium was equal to 6438.47 angstroms. "In 1907, the International Union for Cooperation in Solar Research defined the international angstrom by declaring the wavelength of the red line of cadmium equal to 6438.4696 international angstroms, this definition was endorsed by the International Bureau of Weights and Measures in 1927. From 1927 to 1960, the angstrom remained a secondary unit of length for use in spectroscopy, defined separately from the metre.
In 1960, the metre itself was redefined in spectroscopic terms, which allowed the angstrom to be redefined as being 0.1 nanometres. The angstrom is internationally recognized, but is not a formal part of the International System of Units; the closest SI unit is the nanometre. The International Committee for Weights and Measures discourages its use, it is not included in the European Union's catalogue of units of measure that may be used within its internal market. For compatibility reasons, Unicode includes the formal symbol at U+212B Å ANGSTROM SIGN. However, the angstrom sign is normalized into U+00C5 Å LATIN CAPITAL LETTER A WITH RING ABOVE The Unicode consortium recommends to use the regular letter. Before digital typesetting, the angstrom was sometimes written as "A. U.". This use is evident in Bragg's paper on the structure of ice, which gives the c- and a-axis lattice constants as 4.52 A. U. and 7.34 A. U. respectively. Nowadays the atomic unit of length stands for bohrs, not angstroms. 100 picometres X unit Conversion of units
In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula −C4H9, derived from either of the two isomers of butane. The isomer n-butane can connect in two ways, giving rise to two "-butyl" groups: If it connects at one of the two terminal carbon atoms, it is normal butyl or n-butyl: CH3−CH2−CH2−CH2− If it connects at one of the non-terminal carbon atoms, it is secondary butyl or sec-butyl: CH3−CH2−CH− The second isomer of butane, can connect in two ways, giving rise to two additional groups: If it connects at one of the three terminal carbons, it is isobutyl: 2CH−CH2− If it connects at the central carbon, it is tertiary butyl, tert-butyl or t-butyl: 3C− According to IUPAC nomenclature, "isobutyl", "sec-butyl", "tert-butyl" used to be allowed retained names; the latest guidance changed that: only tert-butyl is kept as preferred prefix, all other butyl-names are removed. In the convention of skeletal formulas, every line ending and line intersection specifies a carbon atom saturated with single-linked hydrogen atoms.
The "R" symbol indicates any other non-specific functional group. Butyl is the largest substituent for which trivial names are used for all isomers; the butyl group's carbon, connected to the rest of the molecule is called the RI or R-prime carbon. The prefixes sec and tert refer to the number of additional side chains connected to the first butyl carbon; the prefix "iso" means "equal" while the prefix'n-' stands for "normal". The four isomers of "butyl acetate" demonstrate these four isomeric configurations. Here, the acetate radical appears in each of the positions where the "R" symbol is used in the chart above: Alkyl radicals are considered as a series, a progression sequenced by the number of carbon atoms involved. In that progression, Butyl is the fourth, the last to be named for its history; the word "butyl" is derived from butyric acid, a four-carbon carboxylic acid found in rancid butter. The name "butyric acid" comes from butter. Subsequent alkyl radicals in the series are named from the Greek number that indicates the number of carbon atoms in the group: pentyl, heptyl, etc.
The tert-butyl substituent is bulky and is used in chemistry for kinetic stabilization, as are other bulky groups such as the related trimethylsilyl group. The effect of the tert-butyl group on the progress of a chemical reaction is called the tert-butyl effect, illustrated in the Diels-Alder reaction below. Compared to a hydrogen substituent, the tert-butyl substituent accelerates the reaction rate by a factor of 240; the tert-butyl effect is an example of steric hindrance
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
In chemistry, a radical is an atom, molecule, or ion that has an unpaired valence electron. With some exceptions, these unpaired electrons make radicals chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes. A notable example of a radical is the hydroxyl radical, a molecule that has one unpaired electron on the oxygen atom. Two other examples are triplet triplet carbene which have two unpaired electrons. Radicals may be generated in a number of ways. Ionizing radiation, electrical discharges, electrolysis are known to produce radicals. Radicals are intermediates in many chemical reactions, more so than is apparent from the balanced equations. Radicals are important in combustion, atmospheric chemistry, plasma chemistry and many other chemical processes. A large fraction of natural products is generated by radical-generating enzymes. In living organisms, the radicals superoxide and nitric oxide and their reaction products regulate many processes, such as control of vascular tone and thus blood pressure.
They play a key role in the intermediary metabolism of various biological compounds. Such radicals can be messengers in a process dubbed redox signaling. A radical may be otherwise bound. In chemical equations, radicals are denoted by a dot placed to the right of the atomic symbol or molecular formula as follows: C l 2 → U V 2 C l ⋅ Radical reaction mechanisms use single-headed arrows to depict the movement of single electrons: The homolytic cleavage of the breaking bond is drawn with a'fish-hook' arrow to distinguish from the usual movement of two electrons depicted by a standard curly arrow; the second electron of the breaking bond moves to pair up with the attacking radical electron. Radicals take part in radical addition and radical substitution as reactive intermediates. Chain reactions involving radicals can be divided into three distinct processes; these are initiation and termination. Initiation reactions are those, they may involve the formation of radicals from stable species as in Reaction 1 above or they may involve reactions of radicals with stable species to form more radicals.
Propagation reactions are those reactions involving radicals in which the total number of radicals remains the same. Termination reactions are those reactions resulting in a net decrease in the number of radicals. Two radicals combine to form a more stable species, for example: 2Cl·→ Cl2 Radicals can form by breaking of covalent bonds by homolysis; the homolytic bond dissociation energies abbreviated as "ΔH °" are a measure of bond strength. Splitting H2 into 2H•, for example, requires a ΔH ° of +435 kJ·mol-1, while splitting Cl2 into 2Cl• requires a ΔH ° of +243 kJ·mol-1. For weak bonds, homolysis can be induced thermally. Strong bonds require high energy photons or flames to induce homolysis. Radicals or charged species add to non-radicals to give new radicals; this process is the basis of the radical chain reaction. Being prevalent and a diradical, O2 reacts with many organic compounds to generate radicals together with the hydroperoxide radical; this process is related to rancidification of unsaturated fats.
Radicals may be formed by single-electron oxidation or reduction of an atom or molecule. These redox reactions occur in electrochemical cells and in ionization chambers of mass spectrometers. Although radicals are short-lived due to their reactivity, there are long-lived radicals; these are categorized as follows: The prime example of a stable radical is molecular dioxygen. Another common example is nitric oxide. Organic radicals can be long lived if they occur in a conjugated π system, such as the radical derived from α-tocopherol. There are hundreds of examples of thiazyl radicals, which show low reactivity and remarkable thermodynamic stability with only a limited extent of π resonance stabilization. Persistent radical compounds are those whose longevity is due to steric crowding around the radical center, which makes it physically difficult for the radical to react with another molecule. Examples of these include Gomberg's triphenylmethyl radical, Fremy's salt, such as TEMPO, TEMPOL, nitronyl nitroxides, azephenylenyls and radicals derived from PTM and TTM.
Persistent radicals are generated in great quantity during combustion, "may be responsible for the oxidative stress resulting in cardiopulmonary disease and cancer, attributed to exposure to airborne fine particles". Gomberg's free radical can be generated by following reaction in lab - 3C-Cl + Ag === 3C• + AgCl The reason for persistivity of free radicals is either the delocalisation of unpaired electron or the unavailability of unpaired electron to other species due to the screening of neighbouring atoms/groups. Diradicals are molecules containing two radical centers. Multiple radical centers can exist in a molecule. Atmospheric oxygen exists as a diradical in its ground state as triplet oxygen; the low reactivity of atmospheric oxygen is due to its diradical state. Non-radical states of dioxygen are less stable tha
Silicones known as polysiloxanes, are polymers that include any synthetic compound made up of repeating units of siloxane, a chain of alternating silicon atoms and oxygen atoms, combined with carbon and sometimes other elements. They are heat-resistant and either liquid or rubber-like, are used in sealants, lubricants, cooking utensils, thermal and electrical insulation; some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, silicone caulk. More called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms; these silicon atoms are tetravalent. So, silicones are polymers constructed from inorganic-organic monomers. Silicones have in general the chemical formula n, where R is an organic group such as an alkyl or phenyl group. In some cases, organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, crosslinking, silicones can be synthesized with a wide variety of properties and compositions.
They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is a silicone oil; the second largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes. F. S. Kipping coined the word silicone in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone, Ph2CO. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO and Ph2CO had different chemistry; the discovery of the structural differences between Kipping's molecules and the ketones means that silicone is no longer the correct term and that the term siloxanes is correct according to the nomenclature of modern chemistry. Silicone is confused with silicon, but they are distinct substances. Silicon is a chemical element, a hard dark-grey semiconducting metalloid which in its crystalline form is used to make integrated circuits and solar cells.
Silicones are compounds that contain silicon, hydrogen and other kinds of atoms as well, have different physical and chemical properties. Compounds containing silicon-oxygen double bonds, now called silanones but which could deserve the name "silicone", have long been identified as intermediates in gas-phase processes such as chemical vapor deposition in microelectronics production, in the formation of ceramics by combustion; however they have a strong tendency to polymerize into siloxanes. The first stable silanone was obtained in 2014 by others. Most common are materials based on polydimethylsiloxane, derived by hydrolysis of dimethyldichlorosilane; this dichloride reacts with water as follows: n Si2Cl2 + n H2O → n + 2n HClThe polymerization produces linear chains capped with Si-Cl or Si-OH groups. Under different conditions the polymer is a cyclic, not a chain. For consumer applications such as caulks silyl acetates are used instead of silyl chlorides; the hydrolysis of the acetates produce the less dangerous acetic acid as the reaction product of a much slower curing process.
This chemistry is used in many consumer applications, such as adhesives. Branches or cross-links in the polymer chain can be introduced by using organosilicone precursors with fewer alkyl groups, such as methyltrichlorosilane and methyltrimethoxysilane. Ideally, each molecule of such a compound becomes a branch point; this process can be used to produce hard silicone resins. Precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain; when silicone is burned in air or oxygen, it forms solid silica as a white powder and various gases. The dispersed powder is sometimes called silica fume. Silicones exhibit many useful characteristics, including: Low thermal conductivity Low chemical reactivity Low toxicity Thermal stability; the ability to repel water and form watertight seals. Does not stick to many substrates, but adheres well to others, e.g. glass. Does not support microbiological growth.
Resistance to oxygen and ultraviolet light. This property has led to widespread use of silicones in the construction industry and the automotive industry. Electrical insulation properties; because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications. High gas permeability: at room temperature, the permeability of silicone rubber for such gases as oxygen is 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Conversely, silicone rubbers can not be used. Silicone can be developed into rubber sheeting, where it has other properties, such as being FDA compliant; this extends the uses of silicone sheeting to industries that demand hygiene, for example and beverage and pharmaceutical. Silicones are used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical, elec
A silanol is a functional group in silicon chemistry with the connectivity Si–O–H. It is related to the hydroxy functional group found in all alcohols. Silanols are invoked as intermediates in organosilicon chemistry and silicate mineralogy. If a silanol contains one or more organic residue, it is an organosilanol; the first isolated example of a silanol was Et3SiOH, reported in 1871 by Albert Ladenburg. He prepared the “silicol” by hydrolysis of Et3SiOEt. Silanols are synthesized by hydrolysis of halosilanes, alkoxysilanes, or aminosilanes. Chlorosilanes are the most common reactants: R3Si–Cl + H2O → R3Si–OH + HClThe hydrolysis of fluorosilanes requires more forcing reagents, i.e. alkali. The alkoxysilanes of the type R3Si are slow to hydrolyze. Compared to the silyl ethers, silyl acetates are faster to hydrolyze, with the advantage that the released acetic acid is less aggressive. For this reason silyl acetates are sometimes recommended for applications. An alternative route involves oxidation of hydrosilanes.
A wide range of oxidants have been employed including air, peracids and potassium permanganate. In the presence of metal catalysts, silanes undergo hydrolysis: R3Si–H + H2O → R3Si–OH + H2 The Si–O bond distance is about 1.65 Å. In the solid state, silanols engage in hydrogen-bonding. Most silanols have only one OH group, e.g. trimethylsilanol. Known are some silanediols, e.g. diphenylsilanediol. For sterically bulky substituents silanetriols have been prepared. Silanols are more acidic than the corresponding alcohols; this trend contrasts with the fact. For Et3SiOH, the pKa is estimated at 13.6 vs. 19 for tert-butyl alcohol. The pKa of Si2OH is 11; because of their greater acidity, silanols can be deprotonated in aqueous solution the arylsilanols. The conjugate base is called a silanolate. Despite the disparity in acidity, the basicities of the two series are similar. Silanols condense to give disiloxanes: 2 R3SiOH → R3Si-O-SiR3 + H2OThe conversions of silyl halides and ethers to siloxanes proceed via silanols.
The sol-gel process, which entails the conversion of, for example, Si4 into hydrated SiO2, proceeds via silanol intermediates. Silanols exist not only as chemical compounds, but are pervasive on the surface of silica and related silicates, their presence is responsible for the absorption properties of silica gel. In chromatography, derivitization of accessible silanol groups in a bonded stationary phase with trimethylsilyl groups is referred to as endcapping. Organosilanols occur as intermediates in industrial processes such as the manufacturing of silicones. Moreover, organosilanols occur as metabolites in the biodegration of small ring silicones in mammals; some silanediols and silanetriols inhibit hydrolytic enzymes such as thermolysin, acetycholinesterase. Silanol refers to a single compound with the formula H3SiOH; the family SiH4−nn are unstable and are of interest to theoretical chemists. The perhydroxylated silanol, sometimes called orthosilicic acid, is discussed in vague terms, but has not been well characterized