Chemistry- Alkanes and Alkenes

The process of naming compounds allows chemists to communicate formulae in words rather than in chemical symbols. There are, however, a few rules about naming compounds which need to be known in order to write a formula in word form or translate a compound in word form into chemical symbols. Ionic compounds If the compound is ionic, then the name of the cation (usually metal) comes first, followed by the ‘compound’ name of the anion.
To find the compound name of an anion, replace the end of the element’s name with ‘ide’. name of cation + name of anion, suffix ‘ide’ E. g. NaCl: sodium, the cation, first, followed by chlorine changed with the suffix ‘ide’ = sodium chloride If the anion is polyatomic and contains oxygen, then the suffix is ‘ate’. name of cation + name of polyatomic oxygen anion, suffix ‘ate’ E. g. Na2CO3: sodium, the cation, first, followed by a polyatomic group containing carbon and oxygen to form carbonate = sodium carbonate Note:
E. g. MgO: magnesium, the cation, first, followed by oxygen changed with the suffix ‘ide’ because oxygen is the sole ion and not part of a polyatomic group = magnesium oxide Sometimes if the compound contains hydrogen, the word ‘hydrogen’ shortens to ‘bi’ such as with NaHCO3, which is known as sodium hydrogen carbonate or sodium bicarbonate. Hydrogen compounds If the compound contains hydrogen and a metal, the metal comes first, followed by the word ‘hydride’, to denote the hydrogen component. etal + hydride E. g. NaH: sodium, the metal, first, followed by hydrogen changed with the suffix ‘ide’ = sodium hydride If the compound contains hydrogen and a non-metal and does not contain water (H2O), then the hydrogen comes first, followed by the element’s name replaced with the ‘ide’ suffix. hydrogen + non-metal, suffix ‘ide’ E. g. HF: hydrogen first, followed by fluorine changed with the suffix ‘ide’ = hydrogen fluoride If the hydrogen non-metal compound dissolves in water, it tarts with the ‘hydro’ prefix, followed by the element’s name replaced with an ‘ic’ suffix, followed by ‘acid’. hydro(name of element, suffix ‘ic’) acid E. g. HCl: hydro, then chlorine with an ‘ic’ suffix, then ‘acid’ = hydrochloric acid Oxygen compounds When naming ionic compounds that contain oxygen the basic rule is similar. If the compound contains hydrogen and an oxygen anion (oxyanion) and does not contain water, then hydrogen comes first, followed by the element name with the suffix ‘ate’. hydrogen + element, suffix ‘ate’ E. g.

HCO3: hydrogen followed by carbon with the suffix ‘ate’ = hydrogen carbonate The ‘ate’ rule is used for the most common or the only compound made with an oxyanion. Some compounds, however, form more than one type of compound with oxygen and the amount of oxygen will affect the prefixes and suffixes used. This occurs for all oxyanions, with or without hydrogen involved. Table 1. 1: Naming more than one type of oxygen compound Oxygen level| Prefix| Element| Suffix| A little oxygen| hypo-| | -ite| Some oxygen| | | -ite| More oxygen| | | -ate| A lot of oxygen| per-| | -ate|
E. g. Chlorine forms four different oxyanions named: ClO = hypochlorite ClO2 = chlorite ClO3 = chlorate ClO4 = perchlorate The oxygen level corresponds with the relative amounts in different compounds and not necessarily the specific numbers of oxygen atoms. If an element forms just two types of oxyanion compounds, then the suffixes ‘ite’ and ‘ate’ will suffice. If the hydrogen oxyanion compound is dissolved in water, it forms an acid using similar rules, only the ‘ite’ suffix changes to ‘ous’ and the ‘ate’ suffix changes to ‘ic’, followed by the word ‘acid’.
Table 1. 2: Naming more than one type of hydrogen oxyanion acid Oxygen level| Prefix| Element| Suffix| Acid| A little oxygen| hypo-| | -ous| | Some oxygen| | | -ous| | More oxygen| | | -ic| | A lot of oxygen| per-| | -ic| | E. g. The above example with chlorine and oxygen plus hydrogen: HClO = hypochlorous acid HClO2 = chlorous acid HClO3 = chloric acid HClO4 = perchloric acid Covalent compounds If a compound contains two non-metals in a covalent bond, then: * the least electronegative element is named first if the compound contains hydrogen, hydrogen is named first * the number of atoms of each element is indicated by a prefix * if the first element only has one atom the prefix is not used * the name of the element has the suffix ‘ide’ least electronegative + number prefix, most electronegative element, suffix ‘ide’ The prefixes used to number the atoms come from Greek and are as follows: 1 = mono- or mon- 2 = di- 3 = tri- 4 = tetra- 5 = penta- | 6 = hexa- 7 = hepta- 8 = octa- 9 = nona- 10 = deca-| E. g.
CO: carbon, the least electronegative atom, first, followed by the prefix ‘mon’ to indicate one atom of oxygen, the most electronegative atom, with the suffix ‘ide’ = carbon monoxide CO2 carbon, the least electronegative atom, first, followed by the prefix ‘di’ to indicate two atoms of oxygen, the most electronegative atom, with the suffix ‘ide’ = carbon dioxide H2O the prefix ‘di’ to indicate two atoms of hydrogen, which has naming priority, followed by ‘mon’ to indicate one atom of oxygen = dihydrogen monoxide Common names There are a number of common names that chemists like to use instead of the proper scientific names.
Most common names and formulae are well-known. It is recommended that common names and formulae be written down as they are encountered so they can be memorised later. Here are a few examples: Common name | Proper name| Chemical formula| water| dihydrogen monoxide| H2O| baking soda| sodium hydrogen carbonate| NaHCO3| table salt| sodium chloride| NaCl| limestone| calcium carbonate| CaCO3| quartz| silicon dioxide| SiO2| See animation 1. What is an acid? Ancient civilisations had already identified acid as a sour-tasting substance that corroded metal, but confirmation about the exact nature of acid eluded chemists until the 20th century.
Early in the 20th century, a number of chemists developed specific chemical definitions for the term ‘acid’, although many of these definitions refer to subatomic processes, going into much greater depth than required here. The simplest, most general definition is that an acid is a substance that contains hydrogen and which can release hydrogen cations (H+) during a reaction. The strength of an acid depends on its ability to release hydrogen ions – stronger acids release hydrogen ions more readily. Some of the properties of acid are that they: * Dissolve in water to form excess hydrogen ions Are highly reactive and will corrode most metals * Conduct electricity * Have a sour taste (strong acids are dangerous and should not be taste-tested) * Produce a stinging sensation (as above, strong acids should not be handled) There are some common edible acids such as citric acid, which is found in fruits like oranges, lemons and limes, acetic acid, found in vinegar, carbonic acid, which is the ‘fizz’ in soft drinks and dairy products, which contain lactic acid. Examples of other acids include: sulphuric acid, present in batteries; and hydrochloric acid, which breaks down food in your stomach. See image 1.
Acids like vinegar are used to preserve food because many organisms cannot live in an acidic environment. Similarly, fermentation of food can also produce an acidic environment for preservation purposes – vinegar is an acetic acid formed from grapes, lactic acid comes from fermentation of milk. What is a base? Bases are substances with the opposite properties to acids, that is, a base is a substance that accepts hydrogen ions in a reaction. Strong bases will accept more hydrogen ions than weak ones. Alkalis are soluble bases that contain hydroxide ions (OH-). Some properties of bases include that they: Dissolve in water to absorb excess hydrogen ions * Neutralise the effect of acid * Denature (change the molecular structure) of proteins * Have a bitter taste (strong bases are dangerous and should not be taste-tested) * Feel soapy (as above, strong bases should not be handled) Basic substances in everyday use include sodium hydrogen carbonate, also known as sodium bicarbonate, used in baking to help bread rise, sodium carbonate, used to make soap, and magnesium hydroxide, commonly used in indigestion remedies. Because of an ability to denature proteins, basic substances break down grease and make good cleaners.
Considering that the human body is made up of proteins, this makes bases more dangerous for humans than acids. Clarification of terms Before proceeding, it is important to clarify some terms used in experiments with acids and bases. Strong substances are either acids that readily lose hydrogen cations or bases that readily gain hydrogen ions; weak substances less readily lose or gain hydrogen ions. For clarity, concentrated acids and bases are either pure or come dissolved in very little water, while dilute substances are dissolved in a lot of water.
Therefore, strong and weak refer to the chemical reactivity of an acidic/basic substance while dilute and concentrate refer to the ratio of water into which the substance dissolves. Indicators It is also important to learn about some of the ways in which to test the strength of acidic and basic substances, since it is not permitted to taste or touch chemicals in a laboratory environment. Chemical substances are classified as acidic (containing acid), basic (containing base) or neutral (containing neither acid nor base). Chemists have developed a number of methods to test the acidity or alkalinity of a substance using chemical indicators.
These indicators use the pH scale, with measurements from one to 14 based on the activity of hydrogen ions in the solution. Substances with a low pH are acidic. Substances with a reading of seven are neutral while basic solutions will elicit a higher reading. Developed by Danish scientist Soren Sorensen, the pH scale may have come from the German word ‘potenz’ (meaning power or potency) and ‘H’, the chemical symbol for hydrogen. It is also possible the term is derived from the Latin ‘pondus hydrogenii’, which translates to ‘weight of hydrogen’. See animation 1.
Many plants are excellent indicators of pH as they need optimum acidity/alkalinity in the soil to grow. Hydrangeas produce white or blue flowers in acidic soil or pink flowers in basic soil. Blue or red litmus paper, made from a fungal/bacterial growth called lichen, turns red in acid or blue in a base but will not change colour in a neutral solution. A synthetic indicator, bromothymol blue, starts blue and then changes yellow in acid. If placed in a basic or neutral substance it will remain blue. Another indicator would be needed to find out if the substance were neutral or basic.
This demonstrates that when using an indicator it is necessary to observe a change in colour to define whether a substance is acidic, basic or neutral. Most indicators have only two colours. The universal indicator is an instrument that mixes several types of indicators and colours in order to show whether a substance is acidic, basic or neutral. Universal indicators have a colour scale that corresponds to the numbered pH scale. After testing, the colour of the paper is matched to a number on the scale for a more exact reading of acidity or alkalinity. See image 2. Reactions
Since acids and bases are more or less opposite substances, they tend to cancel each other out in a process called neutralisation. This reaction produces a salt and water. acid + base salt + water Neutralisation is commonly used in a number of remedies, such as the treatment of bites and stings. Bluebottles inject a basic substance when they sting, so a weak acid like vinegar (acetic acid) will neutralise a bluebottle sting. Conversely, bee stings are slightly acidic, so a bee sting would be neutralised with a weak base, such as sodium bicarbonate. Seafood gives off an odour due to the basic amines it contains.
An acidic acid substance such as lemon juice is squeezed over it to neutralise the smell. Excess acid in the stomach causes indigestion, so it can be neutralised with a weak base called an antacid. An example of an equation using this format is when hydrochloric acid meets sodium hydroxide to form sodium chloride and water: HCl + NaOH NaCl + H2O Adding an acid to a base does not necessarily mean that the product is automatically neutralised. The strength of each of the reactants must be matched so that all the ions released by the acid find a place with the base.
A strong acid with a weak base will result in an acidic salt, a weak acid with a strong base will result in a basic salt, while acids and bases of the same strength will neutralise completely. Both acidic and metallic substances are highly reactive, which is why acid reacts aggressively in the presence of metal, corroding the metal much faster than moisture and air. The combination of an acid and a metal produces a metallic salt and hydrogen gas in an equation represented like this: acid + metal metallic salt + hydrogen The hydrogen ions are easily lost and replaced by the metallic ions, forming a metallic salt.
The hydrogen then forms molecules with itself, resulting in hydrogen gas. An example of this is sulphuric acid and magnesium producing magnesium sulphate salt and hydrogen gas: H2SO4 + Mg MgSO4 + H2 No Flash, No Problem Highlight to reveal names Formula| Names| N2F6| Dinitrogen Hexafluoride| CO2| Carbon Dioxide| SiF4| Silicon Tetrafluoride| CBr4| Carbon Tetrabromide| NCl3| Nitrogen Trichloride| P2S3| Diphosphorous Trisulfide| CO| Carbon Monoxide| NO2| Nitrogen Dioxide| SF2| Sulfur Difluoride| PF5| Phosphorous Pentafluoride| SO2| Sulfur Dioxide| NO| Nitrogen Monoxide| CCl4| carbon tetrachloride|
P2O5| diphosphorus pentoxide| | | Rules 1. The first element is named first, using the elements name. 2. Second element is named as an Anion (suffix “-ide”) 3. Prefixes are used to denote the number of atoms 4. “Mono” is not used to name the first element Note: when the addition of the Greek prefix places two vowels adjacent to one another, the “a” (or the “o”) at the end of the Greek prefix is usually dropped; e. g. , “nonaoxide” would be written as “nonoxide”, and “monooxide” would be written as “monoxide”. The “i” at the end of the prefixes “di-” and “tri-” are never dropped. Prefix| number indicated| | mono-| 1| | di-| 2| | tri-| 3| | tetra-| 4| | penta-| 5| | hexa-| 6| | hepta-| 7| | octa-| 8| | nona-| 9| | deca-| 10| Carbon Allotropes by siebo— last modified April 20, 2007 – 11:54 The allotropes of carbon are the different molecular configurations (allotropes) that pure carbon can take. Following is a list of the allotropes of carbon, ordered by notability, and extent of industrial use. Diamond Main article: Diamond Diamond is one of the best known allotropes of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewelry.
Diamond is the hardest known natural mineral, making it an excellent abrasive and also means a diamond holds its polish extremely well and retains luster. The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually), unsuitable for use as gemstones and known as bort, are destined for industrial use.
In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 400 million carats (80,000 kg) of synthetic diamonds are produced annually for industrial use—nearly four times the mass of natural diamonds mined over the same period. The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use.
Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil), high-performance bearings, and limited use in specialized windows. With the continuing advances being made in the production ofsynthetic diamond, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as asemiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics.
Significant research efforts in Japan, Europe, and the United Statesare under way to capitalize on the potential offered by diamond’s unique material properties, combined with increased quality and quantity of supply starting to become available from synthetic diamond manufacturers. Each carbon atom in diamond is covalently bonded to four othercarbons in a tetrahedron. These tetrahedrons together form a 3-dimensional network of puckered six-membered rings of atoms. This stable network of covalent bonds and the three dimensional arrangement of bonds that diamond is so strong. Graphite
Main article: Graphite Graphite (named by Abraham Gottlob Werner in 1789, from the Greek ??????? : “to draw/write”, for its use in pencils) is oneof the most common allotropes of carbon. Unlike diamond, graphite is a conductor, and can be used, for instance, as the material in the electrodes of an electrical arc lamp. Graphite holds the distinction ofbeing the most stable form of solid carbon ever discovered. Graphite is able to conduct electricity due to the unpaired fourth electron in each carbon atom. This unpaired 4th electron forms delocalisedplanes above and below the planes of the carbon atoms.
These electrons are free to move, so are able to conduct electricity. However, the electricity is only conducted within the plane of the layers. Graphite powder is used as a dry lubricant. Although it might be thought that this industrially important property is due entirely to the loose interlamellar coupling between sheets in the structure, in fact in a vacuum environment (such as in technologies for use in space), graphite was found to be a very poor lubricant. This fact lead to the discovery that graphite’s lubricity is due to adsorbed air and water between the layers, unlike other layered dry lubricants such as molybdenum disulfide.
Recent studies suggest that an effect called superlubricity can also account for this effect. When a large number of crystallographic defects bind these planes together, graphite loses its lubrication properties and becomes what is known as pyrolytic carbon, a useful material in blood-contacting implants such as prosthetic heart valves. Natural and crystalline graphites are not often used in pure form as structural materials due to their shear-planes, brittleness and inconsistent mechanical properties.
In its pure glassy (isotropic) synthetic forms, pyrolytic graphite and carbon fiber graphite is an extremely strong, heat-resistant (to 3000 °C) material, used in reentry shields for missile nosecones, solid rocket engines, high temperature reactors, brake shoes and electric motor brushes. Intumescent or expandable graphites are used in fire seals, fitted around the perimeter of a fire door. During a fire the graphite intumesces (expands and chars) to resist fire penetration and prevent the spread of fumes. A typical start expansion temperature (SET) is between 150 and 300 degrees Celsius.
Amorphous carbon Main article: Amorphous carbon Amorphous carbon is the name used for carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. While entirely amorphous carbon can be made, most of the material described as “amorphous” actually contains crystallites of graphite [1] or diamond [2]with varying amounts of amorphous carbon holding them together, making them technically polycrystalline or nanocrystalline materials.
Commercial carbon also usually contains significant quantities of other elements, which may form crystalline impurities. Coal and soot are both informally called amorphous carbon. However, both are products of pyrolysis, which does not produce true amorphous carbon under normal conditions. The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount ofimpurities. The highest grade, anthracite, is about 90 percent carbon and 10% other elements. Bituminous coal is about 75-90 percent carbon, and lignite is the name for coal that is around 55 percent carbon.
Fullerenes Main article: Fullerene The fullerenes are recently-discovered allotropes of carbon named after the scientist and architect Richard Buckminster Fuller, but were discovered in 1985 by a team of scientists from Rice University and the University of Sussex, three of whom were awarded the 1996 Nobel Prize in Chemistry. They are molecules composed entirely of carbon, which take the form ofa hollow sphere, ellipsoid, or tube. Spherical fullerenes are sometimes called buckyballs, while cylindrical fullerenes are called buckytubes or nanotubes.
As of the early twenty-first century, the chemical and physical properties of fullerenes are still under heavy study, in both pure and applied research labs. In April 2003, fullerenes were under study for potential medicinal use — binding specific antibiotics to the structure to target resistant bacteria and even target certain cancer cells such as melanoma. Fullerenes are similar in structure to graphite, which is composedof a sheet of linked hexagonal rings, but they contain pentagonal (or sometimes heptagonal) rings that prevent the sheet from being planar. Carbon nanotubes Main article: Carbon nanotube
Carbon nanotubes are cylindrical carbon molecules with novel properties that make them potentially useful in a wide variety of applications (e. g. , nano-electronics, optics, materials applications, etc. ). They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Inorganic nanotubes have also been synthesized. A nanotube (also known as a buckytube) is a member of the fullerene structural family, which also includes buckyballs. Whereas buckyballs are spherical in shape, a nanotube is cylindrical, with at least one end typically capped with a hemisphere of the buckyball structure.
Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers(approximately 50,000 times smaller than the width of a human hair), while they can be up to several centimeters in length. There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Aggregated diamond nanorods Main article: Aggregated diamond nanorods Aggregated diamond nanorods, or ADNRs, are an allotrope of carbon believed to be the least compressible material known to humankind, as measured by its sothermal bulk modulus; aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), while a conventional diamondhas a modulus of 442 GPa. ADNRs are also 0. 3% denser than regular diamond. The ADNR material is also harder than type IIa diamond and ultrahard fullerite. Glassy carbon Main article: Glassy carbon Glassy carbon is a class of non-graphitizing carbon which is widely used as an electrode material in electrochemistry, as well as for high temperature crucibles and as a component of some prosthetic devices.
It was first produced by workers at the laboratories of The General Electric Company, UK, in the early 1960s, using cellulose as the starting material. A short time later, Japanese workers produced a similar material from phenolic resin. The preparation of glassy carbon involves subjecting the organic precursors to a series of heat treatments at temperatures up to 3000oC. Unlike many non-graphitizing carbons, they are impermeable to gases and are chemically extremely inert, especially those which have been prepared at very high temperatures.
It has been demonstrated that the rates of oxidation of certain glassy carbons in oxygen, carbon dioxide or water vapour are lower than those of any other carbon. They are also highly resistant to attack by acids. Thus, while normal graphiteis reduced to a powder by a mixture of concentrated sulphuric and nitric acids at room temperature, glassy carbon is unaffected by such treatment, even after several months. Carbon nanofoam Main article: Carbon nanofoam Carbon nanofoam is the fifth known allotrope of carbon discovered in 1997 by Andrei V.
Rode and co-workers at the Australian National University in Canberra. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web. Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite-like sheets that are given negative curvature by the inclusion of heptagons among the regular hexagonal pattern. This is the opposite of what happens in the case of buckminsterfullerenes, in which carbon sheets are given positive curvature by the inclusion of pentagons.
The large-scale structure of carbon nanofoam is similar to that of an aerogel, but with 1% of the density of previously produced carbon aerogels – only a few times the density of air at sea level. Unlike carbon aerogels, carbon nanofoam is a poor electrical conductor. Lonsdaleite Main article: Lonsdaleite Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond, believed to form when meteoric graphite falls to Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite’s hexagonal crystal lattice.
Lonsdaleite was first identified from the Canyon Diablo meteorite at Barringer Crater (also known as Meteor Crater) in Arizona. It was first discovered in 1967. Lonsdaleite occurs as microscopic crystals associated with diamond in the Canyon Diablo meteorite; Kenna meteorite, New Mexico; and Allan Hills (ALH) 77283, Victoria Land, Antarctica meteorite. It has also been reported from the Tunguska impact site, Russia. Chaoite Main article: Chaoite Chaoite is a mineral believed to have been formed in meteorite impacts.
It has been described as slightly harder than graphite with a reflection colour of grey to white. However, the existence of carbyne phases is disputed – see the entry on chaoite for details. Variability of carbon The system of carbon allotropes ps an astounding range ofextremes, considering that they are all merely structural formations ofthe same element. Between diamond and graphite * Diamond is hardest mineral known to man (10 on Mohs scale), but graphite is one of the softest (1 – 2 on Mohs scale). * Diamond is the ultimate abrasive, but graphite is a very good lubricant. Diamond is an excellent electrical insulator, but graphite is a conductor of electricity. * Diamond is usually transparent, but graphite is opaque. * Diamond crystallizes in the isometric system but graphite crystallizes in the hexagonal system. Between amorphous carbon and nanotubes * Amorphous carbon is among the easiest materials to synthesize, but carbon nanotubes are extremely expensive to make. * Amorphous carbon is completely isotropic, but carbon nanotubes are among the most anisotropic materials ever produced. ALKENE NAMES Root names give the number of carbons in the longest continuous chain.
Alkene names are formed by dropping the “ane” and replacing it with “ene”The following list gives samples:Example: root = propane – drop “ane” = “prop” alkene = “prop” + alkene ending = “ene” = propene | No. of Carbons| Root Name| Formula CnH2n| Structure| 2| ethene| C2H4| CH2=CH2| 3| propene| C3H6| CH2=CHCH3| 4| 1-butene| C4H8| CH2=CHCH2CH3| 5| 1-pentene| C5H10| CH2=CHCH2CH2CH3| Following is a list of alkanes showing their chemical formulas, their names, the number of isomers, and the melting and the boiling point. Please note that, except for the first four alkanes (n=1.. ), their chemical names can be derived from the number of C atoms by using Greek numerical prefixes denoting the number of carbons and the suffix “-ane”. Formula| Name(s)| No. of Isomers| m. p. [°C]| b. p. [°C]| CH4| methane (natural gas)| 1| -183| -162| C2H6| ethane| 1| -172| -89| C3H8| propane; dimethyl methane| 1| -188| -42| C4H10| n-butane; methylethyl methane| 2| -138| 0| C5H12| n-pentane| 3| -130| 36| C6H14| n-hexane| 5| -95| 69| C7H16| n-heptane| 9| -91| 98| C8H18| n-octane| 18| -57| 126| C9H20| n-nonane| 35| -54| 151| C10H22| n-decane| 75| -30| 174|
The simplest organic compounds are hydrocarbons. Hydrocarbons contain only two elements, hydrogen and carbon. A saturated hydrocarbon or alkane is a hydrocarbon in which all of the carbon-carbon bonds are single bonds. Each carbon atom forms four bonds and each hydrogen forms a single bond to a carbon. The bonding around each carbon atom is tetrahedral, so all bond angles are 109. 5°. As a result, the carbon atoms in higher alkanes are arranged in zig-zag rather than linear patterns. Straight Chain Alkanes The general formula for an alkane is CnH2n+2 where n is the number of carbon atoms in the molecule.
There are two ways of writing a condensed structural formula. For example, butane may be written as CH3CH2CH2CH3 or CH3(CH2)2CH3. Rules for Naming Alkanes * The parent name of the molecule is determined by the number of carbons in the longest chain. * In the case where two chains have the same number of carbons, the parent is the chain with the most substituents. * The carbons in the chain are numbered starting from the end nearest the first substituent. * In the case where there are substituents having the same number of carbons from both ends, numbering starts from the end nearest the next substituent. When more than one of a given substituent is present, a prefix is applied to indicate the number of substituents. Use di- for two, tri- for three, tetra- for four, etc. and use the number assigned to the carbon to indicate the position of each substituent. Branched Alkanes * Branched substituents are numbered starting from the carbon of the substituent attached to the parent chain. From this carbon, count the number of carbons in the longest chain of the substituent. The substituent is named as an alkyl group based on the number of carbons in this chain. Numbering of the substituent chain starts from the carbon attached to the parent chain. * The entire name of the branched substituent is placed in parentheses, preceded by a number indicating which parent-chain carbon it joins. * Substituents are listed in alphabetical order. To alphabetize, ignore numerical (di-, tri-, tetra-) prefixes (e. g. , ethyl would come before dimethyl), but don’t ignore don’t ignore positional prefixes such as iso and tert (e. g. , triethyl comes before tertbutyl). Cyclic Alkanes * The parent name is determined by the number of carbons in the largest ring (e. g. , cycloalkane such as cyclohexane). In the case where the ring is attached to a chain containing additional carbons, the ring is considered to be a substituent on the chain. A substituted ring that is a substituent on something else is named using the rules for branched alkanes. * When two rings are attached to each other, the larger ring is the parent and the smaller is a cycloalkyl substituent. * The carbons of the ring are numbered such that the substituents are given the lowest possible numbers. Straight Chain Alkanes # Carbon| Name| Molecular Formula| Structural Formula| 1 | Methane | CH4 | CH4 | 2 | Ethane | C2H6 | CH3CH3 | | Propane | C3H8 | CH3CH2CH3 | 4 | Butane | C4H10 | CH3CH2CH2CH3 | 5 | Pentane | C5H12 | CH3CH2CH2CH2CH3 | 6 | Hexane | C6H14 | CH3(CH2)4CH3 | 7 | Heptane | C7H16 | CH3(CH2)5CH3 | 8 | Octane | C8H18 | CH3(CH2)6CH3 | 9 | Nonane | C9H20 | CH3(CH2)7CH3 | 10 | Decane | C10H22 | CH3(CH2)8CH3 | Alkenes contain carbon-carbon double bonds. They are also called unsaturated hydrocarbons. The molecular formular is CnH2n. This is the same molecular formula as a cycloalkane. Structure of Alkenes 1. The two carbon atoms of a double bond and the four atoms attached to them lie in a plane, with bond angles of approximately 120° . A double bond consists of one sigma bond formed by overlap of sp2 hybrid orbitals and one pi bond formed by overlap of parallel 2 P orbitals Here is a chart containing the systemic name for the first twenty straight chain alkenes. Name| Molecular formula| Ethene| C2H4| Propene| C3H6| Butene| C4H8| Pentene| C5H10| Hexene| C6H12| Heptene| C7H14| Octene| C8H16| Nonene| C9H18| Decene| C10H20| Undecene| C11H22| Dodecene| C12H24| Tridecene| C13H26| Tetradecene| C14H28| Pentadecene| C15H30| Hexadecene| C16H32| Heptadecene| C17H34| Octadecene| C18H36| Nonadecene| C19H38|
Eicosene| C20H40| Did you notice how there is no methene? Because it is impossible for a Carbon to have a double bond with nothing. The Basic Rules: A. For straight chain alkenes, it is the same basic rules as nomenclature of alkanes except change the suffix to “-ene. ” i. Find the Longest Carbon Chain that Contains the Carbon Carbon double bond. (If you have two ties for longest Carbon chain, and both chains contain a Carbon Carbon double bond, then look for most substituted chain. ) ii. Give the lowest possible number to the Carbon Carbon double bond. 1.
Do not need to number cycloalkenes because it is understood that the double bond is in the one position. 2. Alkenes that have the same molecular formula but the location of the doble bonds are different means they are constitutional isomers. 3. Functional Groups with higher priority: iii. Add substituents and their position to the alkene as prefixes. Of course remember to give the lowest numbers possible. And remember to name them in alphabetical order when writting them. iv. Next is identifying stereoisomers. when there are only two non hydrogen attachments to the alkene then use cis and trans to name the molecule.
In this diagram this is a cis conformation. It has both the substituents going upward. (This molecule would be called (cis) 5-chloro-3-heptene. ) Trans would look like this v. On the other hand if there are 3 or 4 non-hydrogen different atoms attached to the alkene then use the E, Z system. E (entgegen) means the higher priority groups are opposite one another relative to the double bond. Z (zusammen) means the higher priority groups are on the same side relative to the double bond. (You could think of Z as Zame Zide to help memorize it. ) In this example it is E-4-chloro-3-heptene.
It is E because the Chlorine and the CH2CH3 are the two higher priorities and they are on opposite sides. vi. A hydroxyl group gets precedence over th double bond. Therefore alkenes containing alchol groups are called alkenols. And the prefix becomes –enol. And this means that now the alcohol gets lowest priority over the alkene. vii. Lastly remember that alkene substituents are called alkenyl. Suffix –enyl. B. For common names i. remove the -ane suffix and add -ylene. There are a couple of unique ones like ethenyl’s common name is vinyl and 2-propenyl’s common name is allyl.