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3 3-1 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic Chemistry 2 ed William H. Brown

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3 3-2 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Chapter 3 Alkanes and and Cycloalkanes Cycloalkanes

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3 3-3 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Structure Hydrocarbon Hydrocarbon: a compound composed only of carbon and hydrogen Saturated hydrocarbon Saturated hydrocarbon: a hydrocarbon containing only single bonds Alkane Alkane: a satuated hydrocarbon whose carbons are arranged in a chain Aliphatic hydrocarbon Aliphatic hydrocarbon: another name for an alkane

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3 3-4 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Structure Shape tetrahedral about carbon all bond angles are approximately 109.5

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3 3-5 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Constitutional Isomerism Constitutional isomers Constitutional isomers: compounds with the same molecular formula but a different connectivity (order of attachment of their atoms) example: C 4 H 10

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3 3-6 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Constitutional Isomerism World population is about 6,000,000,000

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3 3-7 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature Alkanes have the general formula C n H 2n+2

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3 3-8 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature

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3 3-9 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature International Union of Pure and Applied Chemistry (IUPAC) Prefix tells the number of carbon atoms ane Suffix -ane specifies an alkane

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3 3-10 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature IUPAC system

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3 3-11 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature Alkyl groups

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3 3-12 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature Alkyl groups

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3 3-13 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature 1. The general name of an open-chain saturated hydrocarbon is alkane 2.. For a branched-chain hydrocarbon, the alkane corresponding to the longest chain is taken as the parent chain and its name is the root name 3. Groups attached to the parent chain are called substituents each is given a name and a number

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3 3-14 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature 4. If there is one substituent, number from the end of the chain that gives it the lower number

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3 3-15 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature 5. If the same substituent occurs more than once, the number of each carbon of the parent chain on which it occurs is given and the number of times it occurs is shown by di-, tri-, tetra-, etc. 6. If there are two identical substituents, number the chain to give the lower number to the substituent encountered first

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3 3-16 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature 7. If there are two or more different substituents, list them in alphabetical order, and number from the end of the chain that gives the substituent encountered first the lower number

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3 3-17 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature 8. The prefixes di-, tri-, tetra- etc. are not included in alphabetization 9. Neither are hyphenated prefixes such as sec- and tert-. The prefix iso- is not hyphenated, and is included in alphabetization.

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3 3-18 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Classification of C & H Primary (1) C Primary (1) C: a carbon bonded to one other carbon 1 H: a hydrogen bonded to a 1 carbon Secondary (2) C Secondary (2) C: a carbon bonded to two other carbons 2 H: a hydrogen bonded to a 2 carbon Tertiary (3) C Tertiary (3) C: a carbon bonded to three other carbons 3 H: a hydrogen bonded to a 3 carbon Quaternary (4) C Quaternary (4) C: a carbon bonded to four other carbons

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3 3-19 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cycloalkanes General formula C n H 2n Ring sizes from 3 to 30 and more are known five- and six-membered rings are the most common

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3 3-20 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cycloalkanes Line-angle drawings each line represents a C-C bond each angle represents a C

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3 3-21 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. IUPAC - General prefix-infix-suffix prefix prefix shows the number of carbon atoms in the parent infix infix shows the nature of the carbon-carbon bonds in the parent

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3 3-22 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. IUPAC - General suffix suffix shows the class of compound

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3 3-23 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. IUPAC - General prop-en-e = propene eth-an-ol = ethanol but-an-one = butanone but-an-al = butanal pent-an-oic acid = pentanoic acid cyclohex-an-ol = cyclohexanol eth-yn-e = ethyne

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3 3-24 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Conformations Conformation Conformation: any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond staggered conformation staggered conformation: a conformation about a carbon-carbon single bond where the atoms on one carbon are as far apart as possible from atoms on the adjacent carbon

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3 3-25 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Conformations eclipsed conformation: a conformation about a carbon- carbon single bond where atoms on one carbon are as close as possible to the atoms on the adjacent carbon

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3 3-26 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Intramolecular Strain Intramolecular strain Intramolecular strain: strain present in a molecule because of nonbonded interaction strain and angle strain nonbonded interaction strain nonbonded interaction strain: arises when atoms not bonded to each other are forced abnormally close to each other; e.g., eclipsed hydrogens in ethane angle strain angle strain: arises from creation of abnormal bond angles

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3 3-27 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Conformations We see nonbonded interaction strain in the eclipsed conformation of ethane at room temperature, approximately 99% of ethane molecules are in the lower-energy staggered conformation and 1% or less are in the higher- energy eclipsed conformation

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3 3-28 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cyclopentane bond angles in planar cyclopentane are 108, which differs only slightly from 109.5. But there are 10 sets of eclipsed hydrogens the ring puckers to an envelope conformation, with average C-C-C bond angles of 105. Puckering increases angle strain, but reduces the nonbonded interaction strain of eclipsed hydrogens.

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3 3-29 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cyclohexane Chair conformation Chair conformation: the most stable puckered conformation of a cyclohexane ring all bond angles are approx. 109.5 all bonds on adjacent carbons are staggered

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3 3-30 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cyclohexane - chair Six H are equatorial and six are axial

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3 3-31 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cyclohexane Boat conformation Boat conformation: a puckered conformation of a cyclohexane ring in which carbons 1 and 4 are bent toward each other less stable than the chair conformation by +7 kcal/mol

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3 3-32 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cyclohexane There are two equivalent chair conformations all C-H bonds equatorial in one chair are axial in the other, and vice versa

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3 3-33 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Methylcyclohexane Equatorial and axial methyl conformations

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3 3-34 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Example 3.8 Label all axial-axial interactions in this chair conformation

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3 3-35 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Tetrodotoxin Produced in the liver and ovaries of the puffer fish

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3 3-36 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cis-Trans Isomerism Cis-trans isomers have the same molecular formula the same connectivity an arrangement of atoms in space that cannot be interconverted by rotation about single bonds under ordinary conditions

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3 3-37 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cis-trans Isomerism 1,2-dimethylcyclopentane

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3 3-38 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cis-trans Isomerism 1,4-Dimethylcyclohexane planar hexagon representations

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3 3-39 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cis-trans Isomerism trans-1,4-dimethylcyclohexane

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3 3-40 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Cis-trans Isomerism cis-1,4-dimethylcyclohexane

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3 3-41 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Physical Properties Low-molecular-weight alkanes (methane....butane) are gases at room temperature Higher-molecular weight alkanes (pentane, decane, gasoline, kerosene) are liquids at room temperature High-molecular weight alkanes (paraffin wax) are semisolids or solids at room temperature

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3 3-42 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Physical properties Constitutional isomers have different physical properties

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3 3-43 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Oxidation of alkanes Oxidation - the basis for their use as energy sources for heat: natural gas, liquefied natural gas (LPG), fuel oil power: gasoline, diesel, and aviation fuel

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3 3-44 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Sources of alkanes Natural gas 90-95% methane Petroleum gases gasoline, kerosene fuel oil lubricating oils asphalt Coal

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3 3-45 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Gasoline Octane rating Octane rating: the percent 2,2,4-trimethylpentane (isooctane) in a mixture of isooctane and heptane that has equivalent antiknock properties

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3 3-46 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Synthesis gas A mixture of carbon monoxide and hydrogen in varying proportions depending on the means by which it is manufactured

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3 3-47 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. Synthesis Gas Synthesis gas is a feedstock for the industrial production of methanol and acetic acid it is likely that industrial routes to other organic chemicals from coal via methanol will also be developed

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3 3-48 Copyright 2000 by John Wiley & Sons, Inc. All rights reserved. AlkanesandCycloalkanes End Chapter 3