LOGO Course lecturer : Jasmin Šutković 4th November 2015 Organic Chemistry – FALL 2015 Lecture 4 : Alkanes

Contents International University of Sarajevo 12.1 Introduction 12.2 Simple Alkanes 12.3 An Introduction to Nomenclature 12.4 Alkane Nomenclature 12.5 Cycloalkanes 12.6 FOCUS ON THE ENVIRONMENT: Fossil Fuels 12.7 Physical Properties 12.8 FOCUS ON THE ENVIRONMENT: Combustion Book chapter 12

Introduction  Alkanes are hydrocarbons having only C-C and C-H single bonds.  The carbons of an alkane can be joined together to form chains or rings of atoms.

 Alkanes that contain chains of carbon atoms but no rings are called acyclic alkanes.  An acyclic alkane has the molecular formula CnH2n + 2, where n is the number of carbons it contains.  Acyclic alkanes are also called saturated hydrocarbons because they have the maximum number of hydrogen atoms per carbon.

We will start with smaller molecules, small number of C atoms. Mehane (CH4) and Ethanne (C2H6) Simple Alkanes – Acyclic alkanes

Common fetures of Alkanes Single bonds! Have isomers...starting with Propane, Butane.... Isomer = samle molecular formula but different structures

Constitutional isomers

Cis and Trans isomerism

Alkanes having 5 or more C atoms

Example problem

The most common multiple bond between C and a heteroatom is carbon – oxygen double bond. Carbon forms 4 stable bonds with itself and other elements. Carbon atoms bind together to fotm RINGS or CHAINS

CLASSIFICATION OF Carbon atoms

Functional groups  The structural features that make it possible to classify compounds into families are called functional groups.  A functional group is a group of atoms within a molecule that has a characteristic chemical behavior

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Nomenclature

 Hydrocarbon chains where all the bonds between carbons are SINGLE bonds  Name uses the ending –ane  Examples: Methane, Propane, Butane, Octane, 2-methylpentane

Summary: IUPAC Rules for Alkane Nomenclature 1. Find and name the longest continuous carbon chain. This is called the parent chain. (Examples: methane, propane, etc.) 1. Find and name the longest continuous carbon chain. This is called the parent chain. (Examples: methane, propane, etc.) 2. Number the chain consecutively, starting at the end nearest an attached group (substituent). 2. Number the chain consecutively, starting at the end nearest an attached group (substituent). 3. Identify and name groups attached to this chain. (Examples: methyl-, bromo-, etc.) 3. Identify and name groups attached to this chain. (Examples: methyl-, bromo-, etc.) 4. Designate the location of each substituent group with the number of the carbon parent chain on which the group is attached. Place a dash between numbers and letters. (Example: 3-chloropentane) 4. Designate the location of each substituent group with the number of the carbon parent chain on which the group is attached. Place a dash between numbers and letters. (Example: 3-chloropentane) 5. Assemble the name, listing groups in alphabetical order. The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing. Place a comma between multiple numbers. (Example: 2,3-dichloropropane) 5. Assemble the name, listing groups in alphabetical order. The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing. Place a comma between multiple numbers. (Example: 2,3-dichloropropane)

Step 1. Find the parent chain.  Where is the longest continuous chain of carbons?

Prefixes for # of Carbons 1Meth6Hex 2Eth7Hept 3Prop8Oct 4But9Non 5Pent10Dec

Endings  Alkanes (all C-C single bonded parent chain) end in –ane  Methane CH 4  Ethane C 2 H 6  Propane C 3 H 8  Attached carbon groups (substituents) end in –yl  Methyl CH 3 -  Ethyl CH 3 CH 2 -  Propyl CH 3 CH 2 CH 2 – 3-ethylpentane

Step 2. Number the parent chain.  Number the parent chain so that the attached groups are on the lowest numbers Methyl is on carbon #2 of the parent chain Methyl is on carbon #4 of the parent chain GREEN is the right way for this one! Groups on 2, 3, and 5 Groups on 4, 6, and Groups on 2 and Groups on 3 and 6

Step 3. Name the attached groups.  Carbon (alkyl) groups  Methyl CH 3 -  Ethyl CH 3 CH 2 -  Propyl CH 3 CH 2 CH 2 –  Halogens  Fluoro (F-)  Chloro (Cl-)  Bromo (Br-)  Iodo (I-)

Step 4. Designate where the group is attached to the parent chain.  Use the numbers of the parent chain from step 2 to designate the location of the attached groups to the parent chain methyl

Step 5. Alphabetize the groups, combine like groups, and assemble.  The prefixes di, tri, tetra etc., used to designate several groups of the same kind  Prefixes are not considered when alphabetizing (Example: dimethyl = m for alphabetizing)  Parent chain goes LAST 1,1,1-trichloro-1- fluoromethane 1,1-dichloro-1,1- difluoromethane

CYCLOALKANES

Examples of cycloalkanes  The smallest alkane that can form a ring is cyclopropane, C 3 H 6, in which the three carbon atoms lie in the same plane.  The angle between adjacent CC bonds is only 60° as seen in the model below:

Molecular models of cycloalkanes cyclohexane cyclopropane cyclobutane cyclopentane

Naming the cycloalkanes:  Find the longest continuous loop of carbon atoms in the skeleton structure.  Name the compound as a derivative of the cycloalkane with this number of carbon atoms:3-C = cyclopropane 4-C = cyclobutane 5-C = cyclopentane

Name the following cycloalkanes: Rings (or cyclic compounds) are composed of rings of carbon and sometimes oxygen or nitrogen. For example, cyclohexane has a ring of six carbon atoms. cyclopropane cyclobutanecyclopentane cyclohexane bromocyclohexane cyclohexene cyclohexane

Examples

Give the IUPAC name

Human life – fossile fuels Alkanes are found in nature, natural gas and petroleum. Natuaral gas and petroleum represents fossile fuels and are used as energy sources Natural gas in composed minimum of 60% methane, rest is ethane, propane and butane. Petroleum is a complex mixture of compounds ( up tp 40 C atoms), giving FUELS.

Focus on environment - combustion Combustion is a form of REDOX reaction – Oxidation – Reduction

Physical properties Alkanes are used primarily as fuels, solvents, and lubricants. Natural gas, gasoline, kerosene, heating oil, lubricating oil, and paraffin “wax” are all composed primarily of alkanes, with different physical properties resulting from different ranges of molecular weights. Alkanes are hydrophobic Alkanes are good lubricants and preservatives for metals because they keep water from reaching the metal surface and causing corrosion.

Boiling point

Major uses of Alkanes

Chemical reactions Homework 2 1. Combustion 2. Halogation 3.Use of Methane 2 page essay with few examples !!!!