9.2- Hydrocarbons |
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-Hydrocarbons are compounds containing only carbon and hydrogen atoms -Hydrocarbons are the basis for synthesizing products like fuels, plastics -Refining is the technology that separates complex mixtures into purified components -Refining could include physical processes such as crushing and treating with solvents, solvent absorption, condensation, and distillation -Fractional distillation also called fractionation, is the process in which the differences in boiling points of the compounds making up petroleum enables the separation of these compounds -In a fractionating tower, crude oil is placed and heated at the bottom of the tower. Compounds with low boiling points vaporize and rise to the top of the tower and gradually condense. Substances that have high boiling points condense in the lower, hotter parts of the tower. -At various levels in the tower, trays collect mixtures of substances as they condense, each mixture containing compounds with similar boiling points -These mixtures are called petroleum fractions. -Fractions that have low boiling points are due to the fact that small molecules have smaller electrons unlike high boiling points containing large molecules -Cracking is the process in which hydrocarbons are broken down into smaller fragments occurring the absence of air eg. C17H36 => C9H20 + C8H16 -Reforming reaction is the opposite of cracking where large molecules are formed from smaller ones eg. C5H12 + C5H12 => C10H22 + H2 -It is used to convert low-grade gasolines into higher grades -Combustion is the process in which petroleum in used as fuels to produce energy eg. 2C8H18 + 25O2 => 16CO2 + 18H20 + energy -Alkanes are hydrocarbons whose empirical formula indicate only single carbon-to-carbon bonds -Each formula in the alkane series has one more CH2 group than the one preceding it eg. CH4 – methane , C2H6 – ethane -The general formula for all alkanes is CnHn+2 -The prefixes of alkane indicate the number of carbon atoms in the molecule -A branch is any group of atoms that is not part of the main structure of the molecule -In naming alkyl branches, the prefixes are followed by a –yl suffix
H H H H | | | | H-C1-C2-C3-C4-H | | | | H H H H -Next, name the branch and their location number on the parent chain
H
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H-C-H <= methyl branch, located at #2 on parent chain
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H | H H
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H-C-C-C-C-H
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H H H H
-Write the complete IUPAC name following this format: (location of branch)-(branch name)(parent chain)
-When writing the name of the alkane, the branches could be listed in alphabetical order or in the order of complexity -Cyclic hydrocarbons are hydrocarbons with a closed ring -If all the carbon-carbon bonds in a cyclic hydrocarbon are single bonds, the compound is a cycloalkane. eg. CH2 / \ CH2-CH2 -Hydrocarbons containing double or triple bonds are valuable in the petrochemical industry because they are the basis for manufacturing many products like plastic -Organic compounds with carbon-carbon double bonds are said to be unsaturated because fewer hydrogen atoms would be attached to the carbon atoms than that if all the bonds were single -Addition reaction are when unsaturated hydrocarbons react with small diatomic molecules such as bromine and hydrogen -Adding sufficient quantity, called hydrogenation, converts unsaturated hydrocarbons to saturated ones -Alkenes are hydrocarbons with carbon-carbon double bonds -Alkenes with only one double bond features the same prefixes used in naming alkanes, together with the suffix –ene -The general formula for all alkenes are C2H2n -Alkynes is explained by the presence of a triple bond between carbon atoms -Alkynes are named like alkenes, except for the –yne suffix -The general formula for all alkynes are CnH2n-2 -In naming alkenes and alkynes, the longest or parent chain must contain the multiple bond, and the chain is numbered form the end closest to the multiple bond -Also, the name of the parent chain is preceded by a number that indicates the position of the multiple bond on the parent chain -The location of the multiple bond in an alkyne precedes over the location of the branches in numbering the carbons of the parent chain -Geometric isomers for alkenes differ from each other with respect to the position of attached groups relative to the double bond -The term cis means that two attached groups are on the same side of the double bond -The term trans means that two attached groups are across from each other
CH3 CH3 CH3 H
\ / \ /
C=C C=C
/ \ / \
H H H CH3
-Aromatic compounds are organic compounds with an aroma or odor
-Aromatics is defined as benzene C6H6, and other carbon compounds with benzene-like structures and properties -Since the properties of benzene could not be explained by the accepted theories of bonding and reactivity, creating a visual model of a molecule of benzene proved difficult -Benzene, C6H6, has a melting point of 5.5°C and boiling point of 80.1°C and its molecules are non-polar. It is very unreactive with bromine, through X-Ray diffraction it shows all carbon-carbon bonds to be of same length -Also, through chemical reactions, it indicates that all carbons in benzene are identical and each carbon is bonded to one hydrogen -In 1865, German architect and chemist August Kekule (1829-1896) proposed a cyclic structure for benzene -Aliphatic compounds are organic compounds with chain or cyclic structures of single, double, or triple bonds -In naming aromatics, if an alkyl is bonded to a benzene ring, it is named as an alkylbenzene -No number is needed of the compound benzene since all carbon atoms are identical to each other -When two hydrogen atoms of the benzene ring have been replaced by an alkyl group, use the lowest pair of numbers to indicate the location of the two alkyl groups on the benzene ring. Numbering starts at one of the substituents and goes clockwise or counterclockwise to obtain the lowest possible pair of numbers -A benzene ring could be considered a branch if placed in larger molecules -In such cases, the benzene ring is called a phenyl group -Cracking = larger molecule + catalyst/heat => smaller molecules -Reforming = small molecules + catalyst/heat => larger molecules or one with more branches -Complete combustion = compound + O2 => CO2 +H2O -Addition (Hydrogenation) = alkene or alkyne + H2 => alkane |
