Science Applied Department (ASD) Centre for Foundation Studies and Extension Education (FOSEE)
PCE 0015 Chemistry for Engineers Foundation in Engineering ONLINE NOTES
Chapter 10
ORGANIC CHEMISTRY
FOSEE , MULTIMEDIA UNIVERSITY (436821-T) MELAKA CAMPUS, JALAN AYER KEROH LAMA, 75450 MELAKA, MALAYSIA. Tel [phone] Fax [phone] URL: http://fosee.mmu.edu.my/~asd/
PCE0015
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Chapter 10
Chapter 10 Part II
10.3 CLASSES OF ORGANIC COMPOUND
A system is needed to simplify the study of organic compounds because of the many different compounds exist. If the chemical study of inorganic compound is simplified with the presence of the Periodic Table, the chemical study of organic compound is simplified with the existence of a homologue series. A homologue series is a group of organic compound that has the same functional group. Functional group is an atom or a group of atom that determine the chemical properties of the compound. According to the functional group, organic compounds are divided into a few classes, as shown in Table 13-1. CLASS 1. Alkane 2. Alkene 3. Alkyne FUNCTIONAL GROUP No EXAMPLE CH4 CH2CHCH3 HCCCH3
CC CC
4. Aromatic hydrocarbon CH3 5. Alkyl halide RX Where X - (Fl, Cl, Br, I) R - alkyl 6. Alcohol 7. Aldehyde OH hydroxyl group O CH O C CH3OH O CH3CH O CH3CCH3 CH3Br
8. Ketone
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9. Ester
O COR NH2
O CH3CO CH3 CH3NH2
10. Amine
Table 13-1: Classes of Organic compound
All organic compounds are derived from a group of compounds known as hydrocarbon (made up of only hydrogen and carbon). On the basis of structure, hydrocarbons are divided into two main classes aliphatic and aromatic.
Fig. 24.1
10.4
ALKANES AND CYCLOALKANES
10.4.1 ALKANES Alkanes have the general formula CnH2n+2, where n = 1, 2, 3, The essential characteristic of alkane molecules is that only single covalent bonds are present. The alkanes are known as saturated hydrocarbon because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms present. Table 10-2 shows the name and the molecular formula of the first 10 straight-chain alkanes.
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NUMBER OF CARBON 1 2 3 4 5 6 7 8 9 10
MOLECULAR FORMULA CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 CH3CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH3 CH3(CH2)5CH3 CH3(CH2)6CH3 CH3(CH2)7CH3 CH3(CH2)8CH3 Table 10-2
NAME
Methane
Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane
When a hydrogen is removed from an alkane, the partial structure that remains is called an alkyl group (CnH2n + 1, generally represented by R).
Isomer
Isomers are compounds that have the same numbers and kinds of atoms but differ in the way the atoms are arranged. Compounds like butane and isobutane, whose atoms are connected differently, are called costitutional isomers (or structural isomers)
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Alkane Nomenclature The nomenclature of alkanes and all other organic compounds is based on the recommendations of the International Union of Pure and Applied Chemistry (IUPAC). Four rules naming for alkanes: 1. Find the longest continuous chain of carbon atoms, and use this chain as the base name. ** when there are two longest chains of equal length, use the chain with the greatest number of substituents as the main chain. 2. Number the longest chain, beginning with the end nearest a branch. 3. Name the substituents on the longest chain (as alkyl groups). Give the location of each substituent by the number of the main-chain carbon atom to which it is attached. 4. When two or more substituents are present, list them in alphabetical order. When two or more of the same alkyl substituents are present, use the prefixes di-, tri-, tetra-, and so on (ignored in alphabetizing) to avoid having to name the alkyl group twice. (**refer textbook page 983)
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Physical Property of Alkanes The phase condition for alkanes are difference depending on the number of carbon in the long chain. Under normal condition, alkanes with one to four carbon atoms are in gas phase; alkanes with five to seventeen carbon atoms are in liquid phase; and alkanes with eighteen carbons onward are in solid phase. Generally, the boiling point and the melting point of alkane increases with the number of carbon atom. The boiling point and the melting point, however, decreases with the existence of branch for the compound with the same number of carbon atoms. The more branches it has the lesser the boiling point and the melting point.
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Chemical Property of Alkanes Alkanes are generally not considered to be very reactive substances. This is because, alkane is a saturated hydrocarbon (it already has the maximum four covalent bonds). Thus, alkane can not undergo an addition reaction. Moreover, the covalent bonds between carbon-carbon and between carbon-hydrogen in alkanes are strong and hardly broken. Thus, alkanes will not undergo a substitution reaction and elimination reaction easily. The reactions that alkanes undergo are combustion, cracking, and halogenation. Combustion is a rapid oxidation that takes place at high temperatures, converting alkanes to carbon dioxide and water. Natural gas, gasoline, and fuel oil are alkanes that undergo highly exothermic combustion reactions: CH4(g) + 2O2(g) 2C2H6(g) + 7O2(g) CO2(g) + 2H2O(l) 4CO2(g) + 6H2O(l)
These, and similar combustion reactions, have long been utilized in industrial processes and in domestic heating and cooking. Halogenation of alkanes is the replacement of one or more hydrogen atoms by halogen atoms when alkanes react with halogens (F2, Br2, Cl2, I2). Heat or light is usually needed to initiate this halogenation process. CH4(g) + Cl2(g) CH3Cl(g) + Methyl chloride HCl(g)
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If an excess of chlorine gas is present, the reaction can proceed further: CH3Cl (g) + Cl2(g) CH2Cl2 (l) + Cl2(g) CHCl3(l) + Cl2(g) CH2Cl2(l) + Methylene chloride CHCl3(l) chloroform + HCl(g) HCl(g) + HCl(g)
CCl4(g) carbon tetrachloride
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