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Chapter 10 Organic Chemistry Copyright McGraw-Hill 2009 1 10.1 Why Carbon Is Different • Electron configuration: [He]2s22p2 effectively prohibits ion formation • Small atomic radius gives rise to short, strong CC bonds and stable compounds • Hybridized atoms (sp- and sp2-) can form strong p bonds with unhybridzed p orbitals • Catenation to form chains and rings containing single, double and triple bonds. Copyright McGraw-Hill 2009 2 Examples of Single and Multiple Bonds Copyright McGraw-Hill 2009 3 Carbon’s lack of d electrons enhances stability Copyright McGraw-Hill 2009 4 Examples of catenation Copyright McGraw-Hill 2009 5 10.2 Classes of Organic Compounds The seemingly limitless variety of organic compounds results from: • Carbon’s ability to form chains by bonding to itself • Presence of elements other than carbon and hydrogen • Functional groups – a group of atoms that determines many of a molecule’s properties • Multiple bonds Copyright McGraw-Hill 2009 6 Copyright McGraw-Hill 2009 7 How are Organic Compounds Named? Alkanes • Identify the longest continuous carbon chain to get the parent name. • Number the carbons in the continuous chain, beginning at the end closest to the substituent. • Identify the substituent and use a number and a prefix to specify location and identity, respectively. Copyright McGraw-Hill 2009 8 Name the compound shown below. H H C H H H H H H H C C C C C C H H H H H H H C H H Copyright McGraw-Hill 2009 9 H H C H H H H H H H C C C C C C H H H H H H H C H H 3,3-dimethylhexane Copyright McGraw-Hill 2009 10 Copyright McGraw-Hill 2009 11 Examples of functional groups Copyright McGraw-Hill 2009 12 Examples of alcohols Copyright McGraw-Hill 2009 13 Electrostatic maps of selected functional groups Copyright McGraw-Hill 2009 14 Naming Specific Functional Groups Alcohols • Identify the longest chain that includes the –OH group. • Change the –e ending to -ol. • Number to give the –OH the lowest number. • When the chain also contains an alkyl substituent, give the –OH the lowest number. Copyright McGraw-Hill 2009 15 Carboxylic Acids • Identify the longest chain that includes the carboxyl group. • Change the –e ending to –oic acid. • Number starting with the carbonyl (C=O) carbon. • Use numbers and prefixes to indicate the position and identity of any substituents. Esters • Name as derivatives of carboxylic acids by replacing the –ic acid ending with -oate. Copyright McGraw-Hill 2009 16 Aldehydes • Identify the longest chain that includes the carbonyl group. • Change the –e ending to -al. • Number starting with the carbonyl (C=O) carbon. • Use numbers and prefixes to indicate the position and identity of any substituents. Copyright McGraw-Hill 2009 17 Ketones • Identify the longest chain that includes the carbonyl group. • Change the –e ending to -one. • Number to give the carbonyl group the lowest possible number. • Use numbers and prefixes to indicate the position and identity of any substituents. Copyright McGraw-Hill 2009 18 Primary Amines • Identify the longest chain that includes the – NH2 group. • Change the –e ending to -amine. • Number starting with the carbon to which the –NH2 group is bonded. • Use numbers and prefixes to indicate the position and identity of any substituents. Primary Amides • Can be named as derivatives of carboxylic acids. • Or, by replacing the –e ending with –amide. Copyright McGraw-Hill 2009 19 Compounds with More Than One Substituent • Prefixes of di, tri, tetra, penta and so forth are used to denote the number of substituents. • Substituent names are alphabetized. • Numbers are used to indicate position of the alphabetized substituents. • Prefixes are not used in alphabetization. Copyright McGraw-Hill 2009 20 Name the following compounds. O CH3 CH3 CH2 CH2 CH3 O CH C CH2 C CH3 OH Copyright McGraw-Hill 2009 21 O CH3 CH2 CH2 C CH3 2-pentanone CH3 CH3 O CH C CH2 OH 3-methylbutanoic acid Copyright McGraw-Hill 2009 22 Identify the functional groups in the following compound. NH2 O C CH3 O O C OH Copyright McGraw-Hill 2009 23 ester O CH3 C amine NH2 O O C OH carboxylic acid Copyright McGraw-Hill 2009 24 10.3 Representing Organic Molecules • Condensed structural formula (Condensed Structure): shows the same information as a structural formula but in condensed form. CH3(CH2)6CH3 • Kekulé structures: similar to Lewis structure but without showing lone pairs H H H C C O H H H Copyright McGraw-Hill 2009 25 • Skeletal Structures: – Consist of straight lines that represent carboncarbon bonds. – Heteroatoms (atoms other than carbon or hydrogen) are shown explicitly NH2 • Resonance: repositioning of electrons shown by curved arrows Copyright McGraw-Hill 2009 26 Copyright McGraw-Hill 2009 27 Copyright McGraw-Hill 2009 28 Write the molecular formula and a structural formula for the following. O Copyright McGraw-Hill 2009 29 O CH3COCH2CH3 C 4H 8O Copyright McGraw-Hill 2009 30 Draw the resonance structures for ozone. O3 O O O O Copyright McGraw-Hill 2009 O O 31 10.4 Isomerism • Constitutional (structural) isomerism occurs when the same atoms can be connected in two or more different ways. • Stereisomerism occurs when atoms are bonded in identical ways but differ in the orientation of those bonds in space. – Geometrical Isomers – Optical Isomers Copyright McGraw-Hill 2009 32 Copyright McGraw-Hill 2009 33 • Geometrical isomers occur in compounds that have restricted rotation around a bond. – cis (same side) – trans (opposite side) Copyright McGraw-Hill 2009 34 • Optical Isomers are nonsuperimposable mirror images of one another. – Such molecules are termed chiral. – A pair of such mirror-image molecules are called enantiomers. – An equimolar mixture of the enantiomers is called a racemic mixture. Copyright McGraw-Hill 2009 35 Copyright McGraw-Hill 2009 36 Bond designations to indicate stereochemistry Copyright McGraw-Hill 2009 37 Measurement of Optical Activity Dextrorotatory – plane of polarization is rotated to the right. Levorotatory – plane of polarization is rotated to the left. Copyright McGraw-Hill 2009 38 10.5 Organic Reactions Important terms • Electrophile – a species with a region of positive or partial positive charge – electron-poor • Nucleophile – a species with a region of negative or partial negative charge – electron-rich Copyright McGraw-Hill 2009 39 Addition Reactions • Reaction involving the addition of a molecule or an ion to another molecule • Electrophilic addition – adding species is an electrophile • Nucleophilic addition – adding species is a nucleophile Copyright McGraw-Hill 2009 40 • Example: electrophilic addition Copyright McGraw-Hill 2009 41 Text Figure 1038 Copyright McGraw-Hill 2009 42 Copyright McGraw-Hill 2009 43 • Example: nucleophilic addition Copyright McGraw-Hill 2009 44 Comparison of electrophilic and nucleophilic addition Copyright McGraw-Hill 2009 45 Substitution Reactions • Reaction when one group is replaced by another. • Electrophilic substitution – an electrophile attacks an aromatic molecule and replaces a hydrogen atom • Nucleophilic substitution – a nucleophile replaces another group on a carbon atom Copyright McGraw-Hill 2009 46 Electrophilic Substitution Reaction Copyright McGraw-Hill 2009 47 Copyright McGraw-Hill 2009 48 Nucleophilic Substitution Reaction Copyright McGraw-Hill 2009 49 Comparison of electrophillic and nucleophillic substitution Copyright McGraw-Hill 2009 50 Other Types of Organic Reactions • Elimination – reaction in which a double bond forms and small molecule is removed • Oxidation-reduction – involve the loss and gain of electrons • Isomerization – one isomer is converted to another Copyright McGraw-Hill 2009 51 • Examples – Elimination – Oxidation-reduction Copyright McGraw-Hill 2009 52 – Isomerization Copyright McGraw-Hill 2009 53 Draw the mechanism for the nucleophilic addition of CN to CH3CHO. Copyright McGraw-Hill 2009 54 Draw the mechanism for the nucleophilic addition of CN to CH3CHO. O H3C C H O + C N H3C C H C N Copyright McGraw-Hill 2009 55 10.6 Organic Polymers • Polymers – molecular compounds made up of many repeating units called monomers • Types – Addition polymers form when monomers join end to end – Condensation polymers form when two different functional groups combine in an elimination reaction • Often are copolymers which are made of two or more different monomers Copyright McGraw-Hill 2009 56 • Addition polymerization Copyright McGraw-Hill 2009 57 Copyright McGraw-Hill 2009 58 • Condensation polymerization Copyright McGraw-Hill 2009 59 • Ester and Ether Formation by Condensation Copyright McGraw-Hill 2009 60 Biological Polymers Naturally occurring polymers include • Proteins – polymers of amino acids • Polysaccharides – polymers of sugars • Nucleic acids – polymers of nucleotides – DNA (deoxyribonucleic acid) – RNA (ribonucleic acid) Copyright McGraw-Hill 2009 61 • Protein formation − Peptide bonds are also called amide linkages since they contain an amide functional group. − Very long chains are called proteins while shorter chains are called polypeptides. Copyright McGraw-Hill 2009 62 Copyright McGraw-Hill 2009 63 Copyright McGraw-Hill 2009 64 • Carbohydrates with different linkages b linkage a linkage Copyright McGraw-Hill 2009 65 • Structure of a nucleotide (found in DNA) Copyright McGraw-Hill 2009 66 Copyright McGraw-Hill 2009 67 Key Points • • • • Unique features of carbon Classes of organic compounds Naming organic compounds Isomerism – Constitutional isomerism – Stereoisomerism • Geometrical isomers • Optical isomers Copyright McGraw-Hill 2009 68 Key Points • Organic reactions – Addition reactions • Electrophilic addition • Nucleophilic addition – Substitution reactions • Electrophilic substitution • Nucleophilic substitution – Elimination reactions – Oxidation-reduction reactions – Isomerization reactions Copyright McGraw-Hill 2009 69 Key Points • Polymers – Addition – Condensation – Biological • Proteins • Carbohydrates • Nucleic Acids Copyright McGraw-Hill 2009 70