Chemistry 121 Winter 17 Introduction to Organic Chemistry and Biochemistry Instructor Dr. Upali Siriwardane (Ph.D. Ohio State) E-mail: upali@latech.edu Office: 311 Carson Taylor Hall ; Phone: 318-257-4941; Contact me trough e-mail if you have questions Online Tests on Following days December 16, 2016: Test 1 (Chapters 12-13) January 23, 2017 : Test 2 (Chapters 14-16) February 10, 2017 : Test 3 (Chapters 17-19) February 22, 2017 : Test 4 (Chapters 20-22) February 23, 2017: Make Up Exam: Chapters 12-22)

GHW Questions GHW#2 CHEM 121 Winter 16

Chapter 12. Saturated Hydrocarbons 12.1 Organic and Inorganic Compounds, 341 12.2 Bonding Characteristics of the Carbon Atom, 342 12.3 Hydrocarbons and Hydrocarbon Derivatives, 342 12.4 Alkanes: Acyclic Saturated Hydrocarbons, 343 12.5 Structural Formulas, 344 12.6 Alkane Isomerism, 346 12.7 Conformations of Alkanes, 348 12.8 IUPAC Nomenclature for Alkanes, 350 12.9 Line-Angle Structural Formulas for Alkanes, 356 12.10 Classification of Carbon Atoms, 358 12.11 Branched-Chain Alkyl Groups, 359 12.12 Cycloalkanes, 361 12.13 IUPAC Nomenclature for Cycloalkanes, 362 12.14 Isomerism in Cycloalkanes, 363 12.15 Sources of Alkanes and Cycloalkanes, 365 12.16 Physical Properties of Alkanes and Cycloalkanes, 367 12.17 Chemical Properties of Alkanes and Cycloalkanes, 368 12.18 Halogenated Alkanes and Cycloalkanes, 371 CHEM 121 Winter 16

Isomerism in Organic Molecules Isomers - different compounds having the same molecular formula but different structural formulas There are two type of Isomers: Constitutional isomerism: Different connections among atoms in the Skeleton Position Functional group Stereoisomerism: Same connectivity among atoms, but these atoms differ in spatial orientation geometric conformational optical CHEM 121 Winter 16

Constitutional Isomers Skeletal (Chp. 12) Functional (Chp. 14) Positional (Chp. 12) Stereoisomers Conformational (Chp.12) Geometric (Chp. 13) Enantiomers (Optical) (Chp. 16) CHEM 121 Winter 16

Constitutional isomers in butane Constitutional isomers: compounds with the same molecular formula but a different connectivity of their atoms in the skeleton. There are two constitutional isomers with molecular formula C4H10 CHEM 121 Winter 16

Constitutional Isomers of Alkanes (CnH2n+2) Number n of carbon Atoms Isomers of CnH2n+2 1 2 3 4 5 6 7 9 8 18 35 10 75 11 159 12 355 13 802 CHEM 121 Winter 16

1. Give the number of constitutional isomers possible in following alkanes. a) CH4 _________ b) C2H6 _________ c) C3H8 _________ d) C4H10 _________ e) C5H12 _________ f) C6H14 _________ g) C7H16 _________ h) C8H18 _________ i) C9H20 _________ CHEM 121 Winter 16

a) Expanded condensed formula: b) Line-angle formula: 2. Give the IUPAC name of the following branched alkane: CH3C(CH3)2CH2CH(CH2CH3)CH2CH3 a) Expanded condensed formula:   b) Line-angle formula: c) Branched Alkyl groups and their names: d) IUPAC name of the compound: CHEM 121 Winter 16

Types of carbon atoms Carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bonded to them. CHEM 121 Winter 16

Types of carbon atoms 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the two different structures of C4H10 Primary = Secondary = Tertiary = Primary = Secondary = Tertiary = CHEM 121 Winter 16

Identify the type of carbon atoms in the following structure CHEM 121 Winter 16

GHW#1: #9 IUPAC name of the following branched alkane: CHEM 121 Winter 16

Reactions of alkanes Combustion CH4(g) + 2O2(g) CO2(g) + 2H2O(g) Many alkanes are used this way - as fuels Methane - natural gas Propane - used in gas grills Butane - lighters Gasoline - mixture of many hydrocarbons, CHEM 121 Winter 16

Reactions of alkanes Halogenation CH4(g) + Cl2(g) CH3Cl(g) + HCl(g) A reaction where a halogen replaces one or more hydrogens. CH4(g) + Cl2(g) CH3Cl(g) + HCl(g) Used to prepare many solvents Dichloromethane, methylene chloride- paint stripper Trichloromethane, Chloroform (CHCl3)- once used as anesthesia 1,2-dichloroethane - dry cleaning fluid heat or light CHEM 121 Winter 16

4. Complete combustion reaction of following alkanes. a) CH4 b) C4H10 c) C5H12 CHEM 121 Winter 16

Cycloalknes Cyclic alkanes: General molecular formula, CnH2n Structure and nomenclature named similar to noncyclic alkanes to name, prefix the name of the corresponding open-chain alkane with cyclo-, and name each substituent on the ring if only one substituent, no need to give it a number if two substituents, number from the substituent of lower alphabetical order if three or more substituents, number to give them the lowest set of numbers, and then list substituents in alphabetical order in planar cyclopentane, all C-C-C bond angles are 108°, which differ only slightly from the tetrahedral angle of 109.5°consequently there is little angle strain CHEM 121 Winter 16

Cycloalkanes :saturated hydrocarbons with a carbon ring Have C-C single bonds in a ring structure. General formula CnH2n cyclobutane cyclopropane CHEM 121 Winter 16

Naming Cycloalkanes Have the carbons connected in a ring. These compounds are known collectively as To name a cycloalkane, use the prefix cyclo- with the parent. If there is only one substituent, a number is not needed. CHEM 121 Winter 16

Cycloalkanes Cycloalkanes have molecular formula CnH2n and contain carbon atoms arranged in a ring. Simple cycloalkanes are named by adding the prefix cyclo- to the name of the acyclic alkane having the same number of carbons. CHEM 121 Winter 16

Naming simple of cycloalkanes: cyclopropane cyclobutane cyclopentane cyclohexane cycloheptane cyclooctane CHEM 121 Winter 16

Ring strain in cycloalkane The stability of cycloalkanes depends on their ability to relieve ring strain when the bond angles are less than 109.5˚. Most stable Least stable CHEM 121 Winter 16

Naming branched cycloalkanes Commonly written as line-angle formulas examples: CHEM 121 Winter 16

IUPAC name of the following substituted cycloakane CHEM 121 Winter 16

Cis and trans Geometrical isomers of Cycloalkanes two groups are said to be located cis to each other if they lie on the same side of a plane. If they are on opposite sides, their relative position is described as trans. CHEM 121 Winter 16

Disubstituted Cycloalkanes There are two different 1,2-dimethylcyclopentanes—one having two CH3 groups on the same side of the ring and one having them on opposite sides of the ring. A and B are isomers. Specifically, they are stereoisomers. CHEM 121 Winter 16

Haloalkanes An alkane in which one or more H atoms is replaced with a halogen (F, Cl, Br, or I) CH3Br 1-bromomethane Br (methyl bromide) CH3CH2CHCH3 2-bromobutane Cl chlorocyclobutane CHEM 121 Winter 16

_________________ _________________ b) CHCl3 c) CCl3F e) CCl2F2 6. Give the common/IUPAC names of following substituted alkanes: Common IUPAC a) CH2Cl2 _________________ _________________ b) CHCl3 c) CCl3F e) CCl2F2 CHEM 121 Winter 16

_________________ _________________ b) CHCl3 c) CCl3F e) CCl2F2 6. Give the common/IUPAC names of following substituted alkanes: Common IUPAC a) CH2Cl2 _________________ _________________ b) CHCl3 c) CCl3F e) CCl2F2 CHEM 121 Winter 16

7. Define following types of terms used in describing isomerism: a) Isomers: An example:   b) Constitutional isomers: An example: CHEM 121 Winter 16

Conformers of Alkanes Structures resulting from the free rotation of a C-C single bond May differ in energy. The lowest-energy conformer is most prevalent. Molecules constantly rotate through all the possible conformations. CHEM 121 Winter 16

Ethane Conformers Staggered conformer has lowest energy. Dihedral angle = 60 degrees H Newman projection Ball & Stick model Dihedral angle H sawhorse H H H H H Staggered Conformation CHEM 121 Winter 16

Ethane Conformers (2) Eclipsed conformer has highest energy Dihedral angle = 0 degrees => Eclipsed Eclipsed Staggered CHEM 121 Winter 16

Conformational Analysis Torsional strain: resistance to rotation. For ethane, only 12.6 kJ/mol => eclipsed staggered eclipsed staggered CHEM 121 Winter 16

Conformational Analysis Butane anti gauche CHEM 121 Winter 16

Conformational Analysis Butane CHEM 121 Winter 15

Stereoisomers c) Conformational stereroisomers: d) Geometric stereoisomers:   e) Optical stereoisomers (d and l Enantiomers): CHEM 121 Winter 16

Geometrical Isomers There are two different 1,2-dimethylcyclopentanes—one having two CH3 groups on the same side of the ring (or double bond) and one having them on opposite sides of the ring (or double bond) . A and B are isomers. Specifically, they are stereoisomers. CHEM 121 Winter 16

Optical Isomers-Enantiomers Dextrorotation and levorotation (refer to the properties of rotating plane polarized light. If the light rotates clockwise (d) as it approaches an observer or light with a anticlockwise rotation (l) CHEM 121 Winter 16

8) Describe the conformational isomerism in following alkanes: a) Butane, C4H10:   b) Cyclopenatane, C5H10: c) Cyclohexane C6H12: CHEM 121 Winter 16

Units of Unsaturation Units of Unsaturation is the number of double (p) bonds and/or rings in the molecule. Each ring or multiple bond replaces 2 H's in the alkane formula CnH2n+2 It relates molecular formula to possible structures CHEM 121 Winter 16

9. Calculate the units of unsaturation in following hydrocarbons a) Butane, C4H10:   b) Cyclopenatane, C5H10: c) Ethene (ethylene), C2H4: d) Cyclohexa-1,3,5-triene (Benzene), C6H6: CHEM 121 Winter 16

Chemical Reactivity of Cycloalkanes Ring strain in cyclopropane and cyclobutane cause them to under go addition reaction like double bond Cycloalkanes with C >4 reacts like akanes undergoing combustion and halogenation CHEM 121 Winter 15