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Phosphine

Phosphine (IUPAC name: phosphane) is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas. Pure phosphine is odourless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphine (P2H4). Phosphines are also a group of organophosphorus compounds with the formula R3P (R = organic derivative). Organophosphines are important in catalysts where they complex to various metal ions; complexes derived from a chiral phosphine can catalyze reactions to give chiral products.

History

Perhaps because of its strong association with elemental phosphorus, phosphine was once regarded as a gaseous form of the element but Lavoisier (1789) recognised it as a combination of phosphorus with hydrogen by describing it as “hydruyet of phosphorus, or phosphuret of hydrogen�.

Thénard (1845) used a cold trap to separate diphosphine from phosphine that had been generated from calcium phosphide, thereby demonstrating that P2H4 is responsible for spontaneous flammability associated with PH3, and also for the characteristic orange/brown colour that can form on surfaces, which is a polymerisation product. He considered diphosphine’s formula to be PH2, and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine. Calcium phosphide (nominally Ca3P2) produces more P2H4 than other phosphides because of the preponderance of P-P bonds in the starting material.

Structure and properties

PH3 is a trigonal pyramidal molecule with C3vmolecular symmetry. The length of the P-H bond 1.42 Å, the H-P-H bond angles are 107°. The dipole moment is 0.58 D, which increases with substitution of methyl groups in the series: CH3PH2, 1.10 D; (CH3)2PH, 1.23 D; (CH3)3P, 1.19 D. In contrast, the dipole moments of amines decrease with substitution, starting with ammonia, which has a dipole moment of 1.47 D. The low dipole moment and almost orthogonal bond angles lead to the conclusion that in PH3 the P-H bonds are almost entirely pσ(P) – sσ(H) and the lone pair contributes only a little to the molecular orbitals. The high positive chemical shift of the P atom in31P NMR spectrum accords with the conclusion that the lone pair electrons occupy the 3s orbital and so are close to the P atom (Fluck, 1973). This electronic structure leads to a lack of nucleophilicity and an inability to form hydrogen bonds.

The aqueous solubility of PH3 is slight; 0.22 mL of gas dissolve in 1 mL of water. Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P-H bonds. It acts as neither an acid nor a base in water. Proton exchange proceeds via a phosphonium (PH4+) ion in acidic solutions and via PH2− at high pH, with equilibrium constants Kb = 4 × 10−28 and Kz = 41.6 × 10−29.

Preparation and occurrence

Phosphine may be prepared in a variety of ways. Industrially it can be made by the reaction of white phosphorus with sodium hydroxide, producing sodium hypophosphite and sodium phosphite as a by-product. Alternatively the acid-catalyzed disproportioning of white phosphorus may be used, which yields phosphoric acid and phosphine. Both routes have industrial significance; the acid route is preferred method if further reaction of the phosphine to substituted phosphines is needed. The acid route requires purification and pressurizing. It can also be made (as described above) by the hydrolysis of a metal phosphide such as aluminium phosphide or calcium phosphide. Pure samples of phosphine, free from P2H4, may be prepared using the action of potassium hydroxide on phosphonium iodide (PH4I).

Phosphine is probably a constituent of the atmosphere at very low and highly variable concentrations and hence may contribute to the global phosphorus biochemical cycle. The origin(s) of atmospheric phosphine is not certain. Possible sources include bacterial reduction of phosphate in decaying organic matter and the corrosion of phosphorus-containing metals.

Phosphines

Related to a PH3 is the class of organophosphorus compounds commonly called "phosphines." These alkyl and aryl derivatives of phosphine are analogous to organic amines. Common examples include triphenylphosphine ((C6H5)3P) and BINAP, both used as chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and commercial names. They are used as flame retardants, fire extinguishants, refrigerants, propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes which contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halon.

Haloalkanes have been known for centuries. Ethyl chloride was produced synthetically in the 15th century. The systematic synthesis of such compounds developed in the 19th century in step with the development of organic chemistry and the understanding of the structure of alkanes. Methods were developed for the selective formation of C-halogen bonds. Especially versatile methods included the addition of halogens to alkenes, hydrohalogenation of alkenes, and the conversion of alcohols to alkyl halides. These methods are so reliable and so easily implemented that haloalkanes became cheaply available for use in industrial chemistry because the halide could be further replaced by other functional groups.

While most haloalkanes are human-produced, non-artificial-source haloalkanes do occur on Earth, mostly through enzyme-mediated synthesis by bacteria, fungi, and especially sea macroalgae (seaweeds). More than 1600 halogenated organics have been identified, with bromoalkanes being the most common haloalkanes. Brominated organics in biology range from biologically-produced methyl bromide to non-alkane aromatics and unsaturates (indoles, terpenes, acetogenins, and phenols). Halogenated alkanes in land plants are more rare, but do occur, as for example the fluoroacetate produced as a toxin by at least 40 species of known plants. Specific dehalogenase enzymes in bacteria which remove halogens from haloalkanes, are also known.

Classes of haloalkanes

From the structural perspective, haloalkanes can be classified according to the connectivity of the carbon atom to which the halogen is attached. In primary (1°) haloalkanes, the carbon that carries the halogen atom is only attached to one other alkyl group. An example is chloroethane (CH3CH2Cl). In secondary (2°) haloalkanes, the carbon that carries the halogen atom has two C-C bonds. In tertiary (3°) haloalkanes, the carbon that carries the halogen atom has three C-C bonds.

Haloalkanes can also be classified according to the type of halogen. Haloalkanes containing carbon bonded to fluorine, chlorine, bromine, and iodine results in organofluorine, organochlorine, organobromine and organoiodine compounds, respectively. Compounds containing more than one kind of halogen are also possible. Several classes of widely used haloalkanes are classified in this way Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These abbreviations are particularly common in discussions of the environmental impact of haloalkanes.

Properties

Haloalkanes generally resemble the parent alkanes in being colorless, relatively odorless, and hydrophobic. Their boiling points are higher than the corresponding alkanes and scale with the atomic weight and number of halides. This is due to the increased strength of the intermolecular forces—from London dispersion to dipole-dipole interaction because of the increased polarity. Thus carbon tetraiodide (CI4) is a solid whereas carbon tetrafluoride (CF4) is a gas. As they contain fewer C-H bonds, halocarbons are less flammable than alkanes, and some are used in fire extinguishers. Haloalkanes are better solvents than the corresponding alkanes because of their increased polarity. Haloalkanes containing halogens other than fluorine are more reactive than the parent alkanes - it is this reactivity that is the basis of most controversies. Many are alkylating agents, with primary haloalkanes and those containing heavier halogens being the most active (fluoroalkanes do not act as alkylating agents under normal conditions). The ozone-depleting abilities of the CFC's arises from the photolability of the C-Cl bond.

Occurrence

Haloalkanes are of wide interest because they are widespread and have diverse beneficial and detrimental impacts. The oceans are estimated to release 1-2 million tons of bromomethane annually.

A large number of pharmaceuticals contain halogens, especially fl

Diamagnetism

Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the magnetic dipole moment. According to Lenz's law, this opposes the external field. Diamagnets are materials with a magnetic permeability less than \mu_0 (a relative permeability less than 1).

Consequently, diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. It is generally quite a weak effect in most materials, although superconductors exhibit a strong effect.

Diamagnetic materials cause lines of magnetic flux to curve away from the material, and superconductors can exclude them completely (except for a very thin layer at the surface).

History

In 1778 S. J. Bergman was the first individual to observe that bismuth and antimony were repelled by magnetic fields. However, the term "diamagnetism" was coined by Michael Faraday in September 1845, when he realized that all materials in nature possessed some form of diamagnetic response to an applied magnetic field.

Diamagnetic materials

Diamagnetism is a very general phenomenon, because all electrons, including the electrons of an atom, will always make a weak contribution to the material's response. However, for materials that show some other form of magnetism (such as ferromagnetism or paramagnetism), the diamagnetism is completely overpowered. Substances that mostly display diamagnetic behaviour are termed diamagnetic materials, or diamagnets. Materials that are said to be diamagnetic are those that are usually considered by non-physicists to be "non-magnetic", and include water, wood, most organic compounds such as petroleum and some plastics, and many metals including copper, particularly the heavy ones with many core electrons, such as mercury, gold and bismuth. The diamagnetism of various molecular fragments are called Pascal's constants.

Diamagnetic materials have a relative magnetic permeability that is less than 1, thus a magnetic susceptibility which is less than 0, and are therefore repelled by magnetic fields. However, since diamagnetism is such a weak property its effects are not observable in every-day life. For example, the magnetic susceptibility of diamagnets such as water is \ \chi_{v} = −9.05×10−6 (SI units). The most strongly diamagnetic material is bismuth, \ \chi_{v} = −1.66×10−4 , although pyrolytic carbon may have a susceptibility of \ \chi_{v} = −4.00×10−4 in one plane. Nevertheless, these values are orders of magnitudes smaller than the magnetism exhibited by paramagnets and ferromagnets.

Superconductors may be considered to be perfect diamagnets (\ \chi_{v} = −1), since they expel all fields (except in a thin surface layer) due to the Meissner effect. However this effect is not due to eddy currents, as in ordinary diamagnetic materials (see the article on superconductivity).

Additionally, all conductors exhibit an effective diamagnetism when they experience a changing magnetic field. The Lorentz force on electrons causes them to circulate around forming eddy currents. The eddy currents then produce an induced magnetic field which opposes the applied field, resisting the conductor's motion.

Demonstrations of diamagnetism

Curving water surfaces

If a powerful magnet (such as a supermagnet) is covered with a layer of water (that is thin compared to the diameter of the magnet) then the field of the magnet significantly repels the water. This causes a slight dimple in the water's surface that may be seen by its reflection.

Diamagnetic levitation

Diamagnets may be levitated in stable equilibrium in a magnetic field, with no power consumption. Earnshaw's theorem seems to preclude the possibility of static magnetic levitation. However, Earnshaw's theorem only applies to objects with positive moments, such as ferromagnets (which have a permanent positive moment) and paramagnets (which induce a positive moment). These are attracted to field maxima, which do not exist in free space. Diamagnets (which induce a negative moment) are attracted to field minima, and there can be a field minimum in free space.

A thin slice of pyrolytic graphite, which is an unusually strong diamagnetic material, can be stably floated in a magnetic field, such as that from rare earth permanent magnets. This can be done with all components at room temperature, making a visually effective demonstration of diamagnetism.

The Radboud University Nijmegen, the Netherlands, has conducted experiments where water and other substances were successfully levitated. Most spectacularly, a live frog (see figure) was levitated.

In September 2009, NASA's Jet Propulsion Laboratory in Pasadena, Ca

Acetonitrile

Acetonitrile is the chemical compound with formula CH3CN. This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture. It is mainly used as a polar aprotic solvent in purification of butadiene.

In the laboratory, it is used as a medium-polarity solvent that is miscible with water and has a convenient liquid range. With a dipole moment of 3.84 D, acetonitrile dissolves a wide range of ionic and nonpolar compounds and is useful as a mobile phase in HPLC and LCMS.

Acetonitrile shortage in 2008-2009

Starting in October 2008, the worldwide supply of acetonitrile was low because Chinese production was shut down for the Olympics. Furthermore, a U.S. factory was damaged in Texas during Hurricane Ike. Owing to the global economic slowdown, the production of acrylonitrile that is used in acrylic fibers and acrylonitrile-butadiene-styrene (ABS) resins decreased. Because acetonitrile is a byproduct in the production of acrylonitrile, its production has also decreased. The global shortage of acetonitrile continued through early 2009.

Applications

Acetonitrile is used mainly as a solvent in the purification of butadiene in refineries.

It is widely used in battery applications because of its relatively high dielectric constant and ability to dissolve electrolytes. For similar reasons it is a popular solvent in cyclic voltammetry. Its low viscosity and low chemical reactivity make it a popular choice for liquid chromatography. Acetonitrile plays a significant role as the dominant solvent used in the manufacture of DNA oligonucleotides from monomers. Industrially, it is used as a solvent for the manufacture of pharmaceuticals and photographic film.

Organic synthesis

Acetonitrile is a common two-carbon building block in organic synthesis of many useful chemicals, including acetophene, thiamine, acetamidine, and α-napthaleneacetic acid. Its reaction with cyanogen chloride affords malononitrile.

Ligand in coordination chemistry

In inorganic chemistry, acetonitrile is employed as a solvent and often an easily displaceable ligand. For example, PdCl2(CH3CN)2 is prepared by heating a suspension of (polymeric) palladium chloride in acetonitrile:

PdCl2 + 2 CH3CN → PdCl2(CH3CN)2

The CH3CN groups undergo rapid displacement by many other ligands.

Production

Acetonitrile is a by-product from the manufacture of acrylonitrile. Production trends for acetonitrile thus generally follow those of acrylonitrile. Acetonitrile can also be produced by many other methods, but these are of no commercial importance as of 2002. Illustrative routes are by dehydration of acetamide or by hydrogenation of mixtures of carbon monoxide and ammonia. The main distributors of acetonitrile in the world are: INEOS, Purification Technologies Inc, BioSolve BV, Carlo Erba Reagents, Panreac, J.T. Baker Chemical, VWR, Sigma Aldrich, and Petrolchem Trading Ltd. In , 32.3 million pounds (14,700 t) of acetonitrile were produced in the US.

Safety

Toxicity

Acetonitrile has only a modest toxicity in small doses. It can be metabolised to produce hydrogen cyanide, which is the source of the observed toxic effects. Generally the onset of toxic effects is delayed, due to the time required for the body to metabolize acetonitrile to cyanide (generally about 2–12 hours).

Cases of acetonitrile poisoning in humans (or, to be more specific, of cyanide poisoning after exposure to acetonitrile) are rare but not unknown, by inhalation, ingestion and (possibly) by skin absorption. The symptoms, which do not usually appear for several hours after the exposure, include breathing difficulties, slow pulse rate, nausea, and vomiting: Convulsions and coma can occur in serious cases, followed by death from respiratory failure. The treatment is as for cyanide poisoning, with oxygen, sodium nitrite, and sodium thiosulfate among the most commonly-used remedies.

It has been used in formulations for nail polish remover, despite its low but significant toxicity. Acetone and ethyl acetate are often preferred as safer for domestic use, and acetonitrile has been banned in cosmetic products in the


From Yahoo Answers

Question:The 2 OH molecules in hydroquinone are attached at the opposite ends of the benzene ring and their dipole moments should cancel each other out, resulting in the net dipole moment = 0. But this is not observed. There is some value of dipole moment present in hydroquinone. Why ??

Answers:These molecules are associated through hydrogen bonding with each other and the dipole moments of para hydroxy groups never cancel each other. They form a linear chain of molecules.

Question:I can't remember how i test for polarity, so can anyone tell me which of these is polar covalent bond? Thanks a million!! 1) NCl3 2) C2H4 3) ZnS 4) Lil 5) AgCl

Answers:1) NCl3 is polar covalent. Polar, because of the difference in electronegativity between N and Cl and covalent because the compound is not a salt (not ionic). Btw, answer 2 is also covalent but is not polar due to symmetry (no molecular dipole moment exists)... Hope this helps!!!

Question:Which of the following statements about boiling points of molecular substances are correct ? a) SO2(l) has a higher boiling point than H2O(l) b) For the boiling points of hydrogen compounds of Group 16 H2Te > H2Se > H2S > H2O c) For the boiling points of hydrogen compounds of Group 17 HF > HI > HBr > HCl d) For the boiling points of hydrogen compounds of Group 14 CH4 > SnH4 > GeH4 > SiH4

Answers:Its either b or c. (A) CaCl2 is is an ionic compound. It is composed of Ca+ ions and Cl- ions in a crystal lattices. The binding force is ionic attraction. (B) LiBr is a solid in a crystal lattice. The ions are bound very tightly together (as it is in the solid phase). The HCl, on the other hand is a gas. There is very little binding force between those molecules, so they bounce around as a gas. (D) CO2 doesn't have a dipole moment. If you draw the molecular structure, you will see that CO2 is linear and symmetric. It basically consists of 2 C-O bonds that, while polar, are opposed and cancel each other out. (E) Hydrogen bonding usually occurs between a species with an -OH and another species with with a =O. But to disprove this statement, just look at Methane. It contains more than 1 H atom but does not experience Hydrogen bonding. Hope that helps!

Question:1. Which of the following compounds would you expect to be ionic? A) H2O B) CO2 C) SrCl2 D) SO2 E) H2S 2. Which of the following would have to gain two electrons in order to achieve a noble gas electron configuration __________? O Sr Na Se Br A) Br B) Sr C) Na D) O, Se E) Sr, O, Se 3. How many hydrogen atoms must bond to silicon to give it an octet of valence electrons? A) 1 B) 2 C) 3 D) 4 E) 5 4. The electron configuration of a Co3+ ion is ____. A) [Ar]3d5 B) [Ar]4s13d5 C) [Ar]4s23d4 D) [Ar]3d6 E) [Ar]4s23d9 5. A polar covalent bond would form between which one of the following pairs of atoms? A) Cl-Cl B) Si-Si C) Ca-Cl D) Cr-Br E) P-Cl 6. The bond between which one of the following pairs of atoms would be the most polar? A) B C B) C N C) C O D) Si O E) C C 7. Which of the following is a useful guideline for the application of formal charges? For neutral molecules: A) a Lewis structure in which there are no formal charges is preferred. B) Lewis structures with large formal charges (+2,+3 and/or -2,-3) are preferred. C) the preferred Lewis structure is one in which positive formal charges are on the most electronegative atoms. 8. A charge of 2+ is most likely to occur for an ion formed from an atom whose electron configuration is 1s22s22p63s23p4. A) True B) False 9. The Si-Cl bond has less ionic character than the C-Cl bond. A) True B) False 10. What is the expected number of valence electrons for an atom of a group 6A element? A) 0 B) 1 C) 2 D) 4 E) 6 11. Which of the following species will have a Lewis structure most like that of the hydronium ion, H3O+? A) NO3- B) NH3 C) SO3 D) CO32- E) H2CO 12. Below are some elements with their number of valence electrons. Which is incorrect? A) Be - 2 B) Br - 5 C) Li - 1 D) Al - 3 E) C - 4 13. The Lewis structure for the carbonate ion, CO32-, shows __________ doubles bond(s), __________ single bond(s) and __________ lone pair(s) on the central atom. A) 3, 1, 2 B) 1, 2, 0 C) 2, 2, 1 D) 2, 1, 1 E) 2, 1, 2 14. Draw the dot formula for acetylene, C2H2. The two carbon atoms are bonded together and each carbon is bonded to one hydrogen. Each carbon-hydrogen bond is a __________ bond and each carbon-carbon bond is a __________ bond. A) single, single B) single, double C) single, triple D) double, single E) double, double 15. Which molecule exhibits resonance? A) BeI2 B) O3 C) H2S D) PF3 E) CO2 16. Which one of the compounds below has the bonds that are the most polar? Electronegativities: H = 2.1, S = 2.5, P = 2.1, As = 2.1, Cl = 3.0, Si = 1.8, Sb = 1.9 A) H2S B) PH3 C) AsCl3 D) SiH4 E) SbCl3 17. Which one of the following molecules contains bonds that are the most polar? Electronegativities: H = 2.1, Be = 1.5, B = 2.0, N = 3.0, F = 4.0, S = 2.5, Br = 2.8, I = 2.5) A) SF6 B) BI3 C) BeBr2 D) NH3 E) NF3 18. Which one of the following molecules has a dipole moment? A) Cl2 B) H2 C) I2 D) BrCl E) N2 19. Which one of the following molecules does not have a dipole moment? A) BrCl B) ClF C) BrF D) O2 E) ICl 20. Which of the following molecules has the most ionic bond character? A) NCl3 B) F2 C) HF D) ClF E) HCl Need help on this. Chem Study guide.

Answers:ok dude, you dont need help, your just being lazy.. i know your gonna be like "ooo just shut up and give me the answers" so im not gonna waste time 1.C 2.B 3.D 4.C or D idk 10. E 12.B do the rest