ic Chapter 2: Alkanes and Cycloalkanes Conformational and Geometric Isomerism
2.1- The Structures of Alkanes * Simplest alkane is methane * Additional alkanes are constructed by lengthening the carbon chain adding an appropriate number of hydrogen to complete the carbon valences. * All alkanes have a general molecular formula of CnH2n+2 * N is the number of carbon atoms * Normal alkanes * Unbranched alkanes * N- alkanes * Methylene Group * A –CH2— * Homologous series * Is a group of organic chemical compounds, usually listed in order of increasing size, that have a similar structure (and hence also similar properties) and whose structures differ only by the number of CH2 units in the main carbon chain.

2.2 Nomenclature of Organic Compounds * IUPAC * International Union of Pure and Applied Chemistry

2.3 IUPAC Rules for Naming Alkanes 1. –ane ending is used for all saturated hydrocarbons 2. Alkanes without branches are number according to the number of carbon atoms 3. Root name a. The longest continuous chain of carbon atoms 4. Substituent b. Are groups attached to the main chain of a molecule c. Alkyl group i. Saturated substituent containing only C and H ii. Taking the name of the alkane with the same number of carbon atoms and changing the –ane to -yl d. Methyl group iii. Derived from methane by removing one of the hydrogen iv. CH3 5. When two or more identical groups are attached to the main chain, prefixes such as di, tri, and tetra are used e. f. 2,3 dimethylpentane g. means there are 1 attached to carbon 2 and one attached to carbon 3 of the five carbon saturated chain 6. If two or more different types of substituents are present, except prefixes such as di- and tri- are not considered. 7. A. Hydrocarbons must be written as one word
B. Numbers are separated from each other by commas
C. Separated from letters by hyphens
D. No space between the last named substituent and the name of the parent alkane.

Summary of the Steps 1. Name the longest continuous carbon chain 2. Number the longest chain beginning at the end of the nearest the first branch point a. If two equally continuous chain, select the one with the most branches b. If there is a branch equidistant from each end, begin number nearest to third chain c. If no third chain, number the substituent nearest the name with alphabetic priority. 3. Write the name as one word, placing the substituents in alphabetic order and using proper punctuation

2.4 Alkyl and Halogen Substituents * Alkly substituents are named by changing the –ane ending of alkanes to –ly * Ethyl group * CH3CH2- or C2H5 * * Propyl group * If a terminal hydrogen is removed * CH3CH2CH2- * * Isopropyl group (or 1- methylethyl) * Hydrogen is removed from the central carbon atom * * 4 different types of butyl groups * Butyl and sec butyl groups are based on n- butane * * Butyl * CH3CH2CH2CH2— * Sec- Butyl * * Isobutyl and tert-butyl groups come from isobutene * R * General symbol for an alkyl group * R—H represents any alkane * R—CL stands for any alkyl chloride * Halogen substituents are named by changing the –ine ending of the element to –o * Ex. F— Floro-, Cl— Chloro-

2.5 Use of the IUPAC Rules

2.6 Sources of Alkanes * Petroleum and natural gas * The two most important natural sources of alkanes * Natural Gas * Consists mainly of methane (about 80%) and ethane (5% to 10%), with lesser amounts of some higher alkanes. * Liquefied to conserve space because 1 cubic meter of liquefied gas is equal to 600 m3 of gas at atmospheric pressure.

2.7 Physical Properties of Alkanes