Chapter 2 Alkanes: Nomenclature and an Introduction to Synthesis

Functional Groups Functional group families are characterized by the presence of a certain arrangement of atoms called a functional group A functional group is the site of most chemical reactivity of a molecule The functional group is responsible for many of the physical properties of a molecule Alkanes do not have a functional groups Carbon-carbon single bonds and carbon-hydrogen bonds are generally very unreactive Chapter 4

Summary of Important Families of Organic Compounds Chapter 4

Summary (cont.) Chapter 4

Classification of Hydrocarbons Most organic compounds are derived from a group of compounds known as hydrocarbons because they are made up of only hydrogen and carbon. Aliphatic hydrocarbons do not contain the benzene group, or the benzene ring. aromatic hydrocarbons contain one or more benzene rings Chapter 4

1- Alkanes (paraffins) Aliphatic Hydrocarbons Alkanes –cycloalkanes - Alkene - Alkyne 1- Alkanes (paraffins) Alkanes have the general formula CnH2n+2 where n = 1,2,3,… only single covalent bonds saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms in the molecule CH4 C2H6 C3H8 methane ethane propane Chapter 4

Shapes of Alkanes “Straight-chain” alkanes have a zig-zag orientation when they are in their most straight orientation. Straight chain alkanes are also called unbranched alkanes Chapter 4

Branched alkanes have at least one carbon which is attached to more than two other carbons Chapter 4

The first 10 Unbranched Alkanes Chapter 4

Physical Properties of Alkanes and Cycloalkanes Boiling points of unbranched alkanes increase smoothly with number of carbons Melting points increase in an alternating pattern according to whether the number of carbon atoms in the chain is even or odd Chapter 4

Nomenclature of Unbranched Alkyl groups The unbranched alkyl groups are obtained by removing one hydrogen from the alkane and named by replacing the -ane of the corresponding alkane with -yl Chapter 4

Nomenclature of Branched-Chain Alkanes (IUPAC) Locate the longest continuous chain of carbons; this is the parent chain and determines the parent name. Number the longest chain beginning with the end of the chain nearer the substituent Designate the location of the substituent When two or more substituents are present, give each substituent a number corresponding to its location on the longest chain Substituents are listed alphabetically Chapter 4

When two or more substituents are identical, use the prefixes di-, tri-, tetra- etc. Commas are used to separate numbers from each other The prefixes are used in alphabetical prioritization When two chains of equal length compete to be parent, choose the chain with the greatest number of substituents When branching first occurs at an equal distance from either end of the parent chain, choose the name that gives the lower number at the first point of difference Chapter 4

Nomenclature of Branched Alkyl Chains Two alkyl groups can be derived from propane Four groups can be derived from the butane isomers Chapter 4

The neopentyl group is a common branched alkyl group Examples Chapter 4

Classification of Hydrogen Atoms Hydrogens take their classification from the carbon they are attached to Chapter 4

Constitutional isomers Constitutional isomers have the same molecular formula but different connectivity of atoms. have different physical properties (melting point, boiling point, densities etc.). Physical Contents of the Hexane Isomers Chapter 4

Number of Alkane Isomers The number of constitutional isomers possible for a given molecular formula increases rapidly with the number of carbons Number of Alkane Isomers Chapter 4

Isomerism Structural Isomerism Stereo Isomerism 1- Skeletal Isomerism 2- Positional Isomerism 3- Functional Isomerism 4- Tautomeric Isomerism Stereo Isomerism 1- Geometric Isomerism 2- Conformational Isomerism 3- Optical Isomerism Chapter 4

Structural Isomerism 1- Skeletal Isomerism Example: Skeletal Isomerism of C6H14 Chapter 4

Structural Isomerism 2- Positional Isomerism Example: Positional Isomerism of C6H14O Chapter 4

Structural Isomerism 3- Functional Isomerism Example 1: Functional Isomerism of C3H6O Ketone Aldehyde Example 2: Functional Isomerism of C2H6O alcohol ether Chapter 4

Structural Isomerism 4- Tautomeric Isomerism Example: Tutomeric Isomerism of C5H8O2 Chapter 4

Synthesis of Alkanes Hydrogenation of Alkenes and Alkynes Chapter 4

Reduction of Alkyl Halides Chapter 4

Chemical reactions of Alkanes 1- Combustion: Alkanes react with oxygen. CO2, H2O, and energy are produced. Alkane + O2 CO2 + H2O + heat CH4 + 2O2 CO2 + 2H2O + energy Chapter 4

Reactions of Alkanes Free Radicals Halogenation Chapter 4

Mechanisms of Free Radicals Halogenation Chapter 4