Acetylene is the simplest alkyne with the formula as C 2 H 2. Alkanes are non-polar compounds and insoluble in water. They have low boiling and melting points. Natural gas, camping gas, lighter gas and much of gasoline are all alkanes.
All the alkanes burn but they need a lot of air or oxygen to burn completely. Alkenes and alkynes are more reactive than alkanes.
Keep your current shopping and add the saved Cart? Remove your current shopping cart and replace with the saved cart? Add the items to your existing shopping cart? The IUPAC system requires first that we have names for simple unbranched chains, as noted above, and second that we have names for simple alkyl groups that may be attached to the chains.
Examples of some common alkyl groups are given in the following table. Note that the "ane" suffix is replaced by " yl " in naming groups. The symbol R is used to designate a generic unspecified alkyl group. Find and name the longest continuous carbon chain. Identify and name groups attached to this chain. Number the chain consecutively, starting at the end nearest a substituent group. Designate the location of each substituent group by an appropriate number and name. Assemble the name, listing groups in alphabetical order.
The prefixes di, tri, tetra etc. Halogen substituents are easily accomodated, using the names: fluoro F- , chloro Cl- , bromo Br- and iodo I-. If the halogen is bonded to a simple alkyl group an alternative "alkyl halide" name may be used. Thus, C 2 H 5 Cl may be named chloroethane no locator number is needed for a two carbon chain or ethyl chloride. For additional examples of how these rules are used in naming branched alkanes, and for some sub-rules of nomenclature Click Here.
Cycloalkanes have one or more rings of carbon atoms. The simplest examples of this class consist of a single, unsubstituted carbon ring, and these form a homologous series similar to the unbranched alkanes. The last yellow shaded column gives the general formula for a cycloalkane of any size. If a simple unbranched alkane is converted to a cycloalkane two hydrogen atoms, one from each end of the chain, must be lost. Hence the general formula for a cycloalkane composed of n carbons is C n H 2n.
Substituted cycloalkanes are named in a fashion very similar to that used for naming branched alkanes. The chief difference in the rules and procedures occurs in the numbering system. Since all the carbons of a ring are equivalent a ring has no ends like a chain does , the numbering starts at a substituted ring atom. For a monosubstituted cycloalkane the ring supplies the root name table above and the substituent group is named as usual.
A location number is unnecessary. If two different substituents are present on the ring, they are listed in alphabetical order, and the first cited substituent is assigned to carbon 1. The numbering of ring carbons then continues in a direction clockwise or counter-clockwise that affords the second substituent the lower possible location number. If several substituents are present on the ring, they are listed in alphabetical order. Location numbers are assigned to the substituents so that one of them is at carbon 1 and the other locations have the lowest possible numbers, counting in either a clockwise or counter-clockwise direction.
The name is assembled, listing groups in alphabetical order and giving each group if there are two or more a location number.
For examples of how these rules are used in naming substituted cycloalkanes Click Here. Small rings, such as three and four membered rings, have significant angle strain resulting from the distortion of the sp 3 carbon bond angles from the ideal This angle strain often enhances the chemical reactivity of such compounds, leading to ring cleavage products. It is also important to recognize that, with the exception of cyclopropane, cycloalkyl rings are not planar flat.
The three dimensional shapes assumed by the common rings especially cyclohexane and larger rings are described and discussed in the Conformational Analysis Section. Hydrocarbons having more than one ring are common, and are referred to as bicyclic two rings , tricyclic three rings and in general, polycyclic compounds. The structural relationship of rings in a polycyclic compound can vary. They may be separate and independent, or they may share one or two common atoms.
Some examples of these possible arrangements are shown in the following table. Hydrocarbons incorporating double or triple carbon-carbon bonds are called unsaturated because hydrogen can be added to the multiple bond, converting the compound to an alkane or cycloalkane. Such compounds are called alkenes and alkynes respectively. Because they are isomeric with cycloalkanes or bicycloalkanes, their names must clearly convey the presence of functional unsaturation.
This is done by changing the ane suffix in the name of an alkane to ene for a double bond, or yne for a triple bond, as illustrated by the following examples.
The location of a multiple bond in a chain is designated by a number, just as is done for substituents on a chain. A complete treatment of alkene and alkyne nomenclature is presented below. Alkenes and alkynes are hydrocarbons which respectively have carbon-carbon double bond and carbon-carbon triple bond functional groups.
The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups:. As noted earlier in the Analysis of Molecular Formulas section, the molecular formula of a hydrocarbon provides information about the possible structural types it may represent.
For example, consider compounds having the formula C 5 H 8. The formula of the five-carbon alkane pentane is C 5 H 12 so the difference in hydrogen content is 4. This difference suggests such compounds may have a triple bond, two double bonds, a ring plus a double bond, or two rings. Some examples were shown above, and there are at least fourteen others! The ene suffix ending indicates an alkene or cycloalkene. The longest chain chosen for the root name must include both carbon atoms of the double bond.
The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent term, indicating the number of double bonds. Each double bond is assigned a locator number.
In cycloalkenes the double bond carbons are assigned ring locations 1 and 2. Which of the two is 1 may be determined by the nearest substituent rule. Identifying isomers from Lewis structures is not as easy as it looks. Lewis structures that look different may actually represent the same isomers.
They are identical because each contains an unbranched chain of four carbon atoms. The International Union of Pure and Applied Chemistry IUPAC has devised a system of nomenclature that begins with the names of the alkanes and can be adjusted from there to account for more complicated structures.
The nomenclature for alkanes is based on two rules:. When more than one substituent is present, either on the same carbon atom or on different carbon atoms, the substituents are listed alphabetically. Because the carbon atom numbering begins at the end closest to a substituent, the longest chain of carbon atoms is numbered in such a way as to produce the lowest number for the substituents. The ending -o replaces -ide at the end of the name of an electronegative substituent in ionic compounds, the negatively charged ion ends with -ide like chloride; in organic compounds, such atoms are treated as substituents and the -o ending is used.
The number of substituents of the same type is indicated by the prefixes di- two , tri- three , tetra- four , and so on for example, difluoro- indicates two fluoride substituents.
The four-carbon chain is numbered from the end with the chlorine atom. This puts the substituents on positions 1 and 2 numbering from the other end would put the substituents on positions 3 and 4.
Four carbon atoms means that the base name of this compound will be butane. The bromine at position 2 will be described by adding 2-bromo-; this will come at the beginning of the name, since bromo- comes before chloro- alphabetically.
The chlorine at position 1 will be described by adding 1-chloro-, resulting in the name of the molecule being 2-bromochlorobutane. We call a substituent that contains one less hydrogen than the corresponding alkane an alkyl group. The name of an alkyl group is obtained by dropping the suffix -ane of the alkane name and adding -yl :.
The open bonds in the methyl and ethyl groups indicate that these alkyl groups are bonded to another atom. Naming Substituted Alkanes Name the molecule whose structure is shown here:. The longest carbon chain runs horizontally across the page and contains six carbon atoms this makes the base of the name hexane, but we will also need to incorporate the name of the branch. In this case, we want to number from right to left as shown by the red numbers so the branch is connected to carbon 3 imagine the numbers from left to right—this would put the branch on carbon 4, violating our rules.
The branch attached to position 3 of our chain contains two carbon atoms numbered in blue —so we take our name for two carbons eth- and attach -yl at the end to signify we are describing a branch. Putting all the pieces together, this molecule is 3-ethylhexane. This diversity of possible alkyl groups can be identified in the following way: The four hydrogen atoms in a methane molecule are equivalent; they all have the same environment.
They are equivalent because each is bonded to a carbon atom the same carbon atom that is bonded to three hydrogen atoms. Removal of any one of the four hydrogen atoms from methane forms a methyl group. Likewise, the six hydrogen atoms in ethane are equivalent and removing any one of these hydrogen atoms produces an ethyl group. Each of the six hydrogen atoms is bonded to a carbon atom that is bonded to two other hydrogen atoms and a carbon atom.
However, in both propane and 2—methylpropane, there are hydrogen atoms in two different environments, distinguished by the adjacent atoms or groups of atoms:. Each of the six equivalent hydrogen atoms of the first type in propane and each of the nine equivalent hydrogen atoms of that type in 2-methylpropane all shown in black are bonded to a carbon atom that is bonded to only one other carbon atom.
The two purple hydrogen atoms in propane are of a second type. They differ from the six hydrogen atoms of the first type in that they are bonded to a carbon atom bonded to two other carbon atoms. The green hydrogen atom in 2-methylpropane differs from the other nine hydrogen atoms in that molecule and from the purple hydrogen atoms in propane.
The green hydrogen atom in 2-methylpropane is bonded to a carbon atom bonded to three other carbon atoms. Two different alkyl groups can be formed from each of these molecules, depending on which hydrogen atom is removed. Note that alkyl groups do not exist as stable independent entities. They are always a part of some larger molecule. The location of an alkyl group on a hydrocarbon chain is indicated in the same way as any other substituent:.
Alkanes are relatively stable molecules, but heat or light will activate reactions that involve the breaking of C—H or C—C single bonds. Combustion is one such reaction:. Alkanes burn in the presence of oxygen, a highly exothermic oxidation-reduction reaction that produces carbon dioxide and water.
As a consequence, alkanes are excellent fuels. For example, methane, CH 4 , is the principal component of natural gas. Butane, C 4 H 10 , used in camping stoves and lighters is an alkane. Gasoline is a liquid mixture of continuous- and branched-chain alkanes, each containing from five to nine carbon atoms, plus various additives to improve its performance as a fuel. Kerosene, diesel oil, and fuel oil are primarily mixtures of alkanes with higher molecular masses. The main source of these liquid alkane fuels is crude oil, a complex mixture that is separated by fractional distillation.
You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids. The vapors rise through bubble caps in a series of trays in the tower. As the vapors gradually cool, fractions of higher, then of lower, boiling points condense to liquids and are drawn off.
No carbon-carbon bonds are broken in these reactions, and the hybridization of the carbon atoms does not change. For example, the reaction between ethane and molecular chlorine depicted here is a substitution reaction:. The C—Cl portion of the chloroethane molecule is an example of a functional group , the part or moiety of a molecule that imparts a specific chemical reactivity.
The types of functional groups present in an organic molecule are major determinants of its chemical properties and are used as a means of classifying organic compounds as detailed in the remaining sections of this chapter. Organic compounds that contain one or more double or triple bonds between carbon atoms are described as unsaturated.
You have likely heard of unsaturated fats. These are complex organic molecules with long chains of carbon atoms, which contain at least one double bond between carbon atoms. Unsaturated hydrocarbon molecules that contain one or more double bonds are called alkenes. Double and triple bonds give rise to a different geometry around the carbon atom that participates in them, leading to important differences in molecular shape and properties.
The differing geometries are responsible for the different properties of unsaturated versus saturated fats. Ethene, C 2 H 4 , is the simplest alkene. Each carbon atom in ethene, commonly called ethylene, has a trigonal planar structure.
Four carbon atoms in the chain of butene allows for the formation of isomers based on the position of the double bond, as well as a new form of isomerism. Ethylene the common industrial name for ethene is a basic raw material in the production of polyethylene and other important compounds. Over million tons of ethylene were produced worldwide in for use in the polymer, petrochemical, and plastic industries. Ethylene is produced industrially in a process called cracking, in which the long hydrocarbon chains in a petroleum mixture are broken into smaller molecules.
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