imported>Milton Beychok |
imported>D. Matt Innis |
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| '''Hydrocarbons''' are a class of [[molecule]]s that contain only [[carbon]] and [[hydrogen]] atoms. Some of them make very good fuels. Gasoline contains a mixture of hydrocarbons. Unsaturated hydrocarbons, which contain one or more double bonds, are useful chemicals for many reactions. | | An '''alkane''' is an organic molecule composed of only carbon and hydrogen, arranged in a straight chain with only single carbon-carbon bonds. Their empirical formula, derived from the number of carbon atoms, n, is C<sub>n</sub>H<sub>2n+2</sub>. |
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| == Linear saturated hydrocarbons ==
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| The simplest hydrocarbons are linear molecules in which each carbon atoms is bonded to two other carbons atoms, in a linear fashion, except for the carbon atoms at the ends, which are only bonded to one other carbon atom. Saturated hydrocarbon names generally end with the suffix "ane" which distinguishes them from unsaturated hydrocarbons, which end with the suffix "ene".
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| Linear saturated hydrocarbons are referred to as '''paraffins''' or '''alkanes'''. Their general formula is C<sub>n</sub>H<sub>n+2</sub>.
| | Names for the first four alkanes are historic, while the names for those with six or more carbons are derived from the Greek prefix for the number of carbon atoms in the molecule. |
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| {| class = "wikitable" | | {| class="wikitable" |
| |+ Some example alkanes <ref name=56thHndbk>{{cite book|author=Robert C. Weast (Editor)|title=Handbook of Chemistry and Physics|edition=56th Edition|publisher=CRC Press|year=1975|id=ISBN 0-87819-455-X}}</ref>
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| ! Name!!Formula!!C<sub>n</sub>H<sub>2n+2</sub>
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| | [[Methane]]|| CH<sub>4</sub>||CH<sub>4</sub>
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| | [[Ethane]] || CH<sub>3</sub>–CH<sub>3</sub>||C<sub>2</sub>H<sub>6</sub>
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| | [[Propane]]|| CH<sub>3</sub>–CH<sub>2</sub>–CH<sub>3</sub>||C<sub>3</sub>H<sub>8</sub>
| | ! IUPAC name |
| | ! Carbons |
| | ! Column 3 Header |
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| | [[Butane]]|| CH<sub>3</sub>–(CH<sub>2</sub>)<sub>2</sub>–CH<sub>3</sub>||C<sub>4</sub>H<sub>10</sub> | | | Methane |
| | | 1 |
| | | CH<sub>4</sub> |
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| | [[Pentane]]|| CH<sub>3</sub>–(CH<sub>2</sub>)<sub>3</sub>–CH<sub>3</sub>||C<sub>5</sub>H<sub>12</sub> | | | Ethane |
| | | 2 |
| | | CH<sub>3</sub>CH<sub>3</sub> |
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| | [[Hexane]]|| CH<sub>3</sub>–(CH<sub>2</sub>)<sub>4</sub>–CH<sub>3</sub>||C<sub>6</sub>H<sub>14</sub> | | | Propane |
| | | 3 |
| | | CH<sub>3</sub>CH<sub>2</sub>CH<sub>3</sub> |
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| | [[Heptane]]||CH<sub>3</sub>–(CH<sub>2</sub>)<sub>5</sub>–CH<sub>3</sub>||C<sub>7</sub>H<sub>16</sub> | | | Butane |
| | | 4 |
| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>CH<sub>3</sub> |
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| | [[Octane]]||CH<sub>3</sub>–(CH<sub>2</sub>)<sub>6</sub>–CH<sub>3</sub>||C<sub>8</sub>H<sub>18</sub> | | | Pentane |
| | | 5 |
| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>CH<sub>3</sub> |
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| | [[Nonane]]||CH<sub>3</sub>–(CH<sub>2</sub>)<sub>7</sub>–CH<sub>3</sub>||C<sub>9</sub>H<sub>20</sub> | | | Hexane |
| | | 6 |
| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>CH<sub>3</sub> |
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| | [[Decane]]||CH<sub>3</sub>–(CH<sub>2</sub>)<sub>8</sub>–CH<sub>3</sub>||C<sub>10</sub>H<sub>22</sub> | | | Heptane |
| |} | | | 7 |
| | | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>5</sub>CH<sub>3</sub> |
| == Linear unsaturated hydrocarbons ==
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| | | | Octane |
| Unsaturated hydrocarbons are useful precursor molecules for many reactions. Because they contain one or more double bonds, a large variety of chemical transformations are possible. Unsaturated hydrocarbons generally end with the "ene" suffix, although common names are sometimes used instead of the IUPAC designation. In addition, a numerical prefix is used to indicate the position of the double bond(s).
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| | | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>CH<sub>3</sub> |
| Linear unsaturated hydrocarbons containing a single double bond are referred to as '''olefins''' or '''alkenes'''. Their general formula is C<sub>n</sub>H<sub>2n</sub>.
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| {| class = "wikitable"
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| |+ Some example alkenes <ref name=56thHndbk/> | |
| ! Name!!Formula!!C<sub>n</sub>H<sub>2n</sub>
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| | [[Ethene]]|| CH<sub>2</sub>=CH<sub>2</sub>||C<sub>2</sub>H<sub>4</sub>
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| | [[Propene]] || CH<sub>2</sub>=CH–CH<sub>3</sub>||C<sub>3</sub>H<sub>6</sub>
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| | [[1-Butene]]|| CH<sub>2</sub>=CH–CH<sub>2</sub>–CH<sub>3</sub>||C<sub>4</sub>H<sub>8</sub> | | | Nonane |
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| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>CH<sub>3</sub> |
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| | [[2-Butene]]|| CH<sub>3</sub>–CH<sub></sub>=CH<sub></sub>–CH<sub>3</sub> ||C<sub>4</sub>H<sub>8</sub> | | | Decane |
| | | 10 |
| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>CH<sub>3</sub> |
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| | [[1-Pentene]]|| CH<sub>2</sub>=CH–(CH<sub>2</sub>)<sub>2</sub>–CH<sub>3</sub>||C<sub>5</sub>H<sub>10</sub> | | | Undecane |
| | | 11 |
| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>9</sub>CH<sub>3</sub> |
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| | [[1-Hexene]]|| CH<sub>2</sub>=CH–(CH<sub>2</sub>)<sub>3</sub>–CH<sub>3</sub>||C<sub>6</sub>H<sub>12</sub> | | | Dodecane |
| | | 12 |
| | | CH<sub>3</sub>(CH<sub>2</sub>)<sub>10</sub>CH<sub>3</sub> |
| |} | | |} |
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| Linear unsaturated hydrocarbons containing two double bonds are referred to as '''dienes''', '''diolefins''' or '''alkadienes'''. Their general formula is C<sub>n</sub>H<sub>2(n-1)</sub> and some example dienes are:<ref name=56thHndbk/>
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| * [[1,2-Butadiene]]: CH<sub>2</sub>=C=CH–CH<sub>3</sub> or C<sub>4</sub>H<sub>6</sub>
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| * [[1,2-Pentadiene]]: CH<sub>2</sub>=C=CH–CH<sub>2</sub>–CH<sub>3</sub> or C<sub>5</sub>H<sub>8</sub>
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| Linear unsaturated hydrocarbons containing a triple bond are referred to as '''alkynes'''. The simplest example is [[ethyne]] ([[acetylene]]): H–C≡C–H or C<sub>2</sub>H<sub>2</sub>
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| == Cyclic saturated hydrocarbons ==
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| {{Image|Example Cycloalkanes.png|right|285px|Example cycloalkanes.<ref name=56thHndbk/>}}
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| Cyclic saturated hydrocarbons have a closed ring of carbon atoms in a polygon configuration having the same number of vertices as the number of carbon atoms, with each carbon atom being bonded to two hydrogen atoms and to two other carbon atoms. They are referred to as '''cycloalkanes''', '''cycloparaffins''' or '''naphthenes'''.
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| Cycloalkanes with a single ring of carbon atoms have a general formula of C<sub>n</sub>H<sub>2n</sub>. The adjacent image depicts two such single ring cycloalkanes, namely [[cyclopentane]] (C<sub>5</sub>H<sub>10</sub>) and [[cyclohexane]] (C<sub>6</sub>H<sub>12</sub>).
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| Cycloalkanes may also have two fused (i.e., conjoined) rings. For example, two cyclohexane rings may be fused, so that two of the carbon atoms are shared by each of the two rings, to form [[decalin]] (C<sub>10</sub>H<sub>18</sub>) which is referred to as a '''bicycloalkane'''.
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| The general formula for cycloalkanes is C<sub>n</sub>H<sub>2(n+1-g)</sub> where g is the number of rings.
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| == Cyclic unsaturated hydrocarbons ==
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| {{Image|Example Cycloalkenes.png|right|278px|Example cycloalkenes.<ref name=56thHndbk/>}}
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| Cyclic unsaturated hydrocarbons have a closed ring of carbon atoms in a polygon configuration having the same number of vertices as the number of carbon atoms. If the hydrocarbons have a ring containing a single double bond between two of the carbons, the hydrocarbons are referred to as '''cycloalkenes''' or '''cycloolefins'''. The adjacent image depicts two such cycloalkenes with single double bonds, namely [[cyclopentene]] (C<sub>5</sub>H<sub>8</sub>) and [[cyclohexene]] (C<sub>6</sub>H<sub>10</sub>).
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| The general formula for single-ring cycloalkenes with a single double bond is C<sub>n</sub>H<sub>2n-2</sub>.
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| If single-ring alkenes have two double bonds, they are referred to as '''cyclodienes''' or '''cyclodiolefins'''. An example is [[cyclopentadiene]] (C<sub>5</sub>H<sub>6</sub>), and the general formula for single-ring cycloalkenes with two double bonds is C<sub>n</sub>H<sub>2n-4</sub>.
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| == Aromatic hydrocarbons ==
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| {{Image|Example Aromatics.png|right|396px|Example aromatics.<ref name=56thHndbk/>}}
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| Aromatic hydrocarbons have a closed ring of 6 carbon atoms in the shape of a hexagon with 3 of the carbon atoms having a double bond with one connected carbon atom and a single bond with another connnected carbon. The are generally referred to as '''aromatics''' or '''aryl compounds'''.
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| The adjacent image depicts three of the most common aromatics, namely [[benzene]] (C<sub>6</sub>H<sub>6</sub>), [[toluene]] (C<sub>7</sub>H<sub>8</sub> and [[o-xylene]] (C<sub>8</sub>H<sub>10</sub>). There are three possible [[xylene]]s referred to as ortho-xylene (o-xylene), meta-xylene ([[m-xylene]]) and para-xylene ([[p-xylene]]).
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| Aromatics may have two or more rings, either in fused or other configurations, and may have many different side groups or side chains (such as the methyl side group in toluene). There are quite literally hundreds (if not thousands) of various aromatic hydrocarbons.
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| == References ==
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| {{reflist}}
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