Chemistry 121(01) Winter 2014 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; Office Hours: MTW 9:00 am - 11:00 am; TR 9:00-10:00 am & 1:00-2:00 pm. December 20, Test 1 (Chapters 12-13) January 24 Test 2 (Chapters 14-16) February 14 Test 3 (Chapters 17-19) February 26, Test 4 (Chapters 20-22) February 27, 2014, Make Up Exam: Bring Scantron Sheet 882-E 1
GHW Questions GHW#2
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
Isomerism 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
Constitutional Isomers CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 3 Positional (Chp. 12) CH 3 CH 2 CH 2 CH 3 CH CH 3 Br Br Stereoisomers Geometric (Chp. 13) H H C C Br Br H Br C C Br H H Skeletal (Chp. 12) CO 2 H C OH CH 3 H H Functional (Chp. 14) CH 3 CH 2 OH CH 3 OCH 3 Conformational (Chp.12) CH 3 CH 3 H H HH H O CH 3 CH 3 HH Enantiomers (Optical) (Chp. 16) CO 2 H C H CH 3
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 C 4 H 10 CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 3 Butane 2-Methylpropane (bp -0.5 C) (bp -11.6 C)
Isomers of Alkanes (C n H 2n+2 ) Number n of carbon Atoms Isomers of C n H 2n+2 1 1 2 1 3 1 4 2 5 3 6 5 7 9 8 18 9 35 10 75 11 159 12 355 13 802
1. Give the number of constitutional isomers possible in following alkanes. a) CH 4 b) C 2 H 6 c) C 3 H 8 d) C 4 H 10 e) C 5 H 12 f) C 6 H 14 g) C 7 H 16 h) C 8 H 18 i) C 9 H 20
2. Give the IUPAC name of the following branched alkane: CH 3 C(CH 3 ) 2 CH 2 CH(CH 2 CH 3 )CH 2 CH 3 a) Expanded condensed formula: b) Line-angle formula: c) Branched Alkyl groups and their names: d) IUPAC name of the compound:
Types of carbon atoms Carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bonded to them. 10
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 C 4 H 10 H H H H H C C C C H H H H H H H C H H H C C H C H H H H Butane, C 4 H 10 Primary =? Secondary = Tertiary = Isobutane, C 4 H 10 Primary = Secondary = Tertiary =
3. Identify the type of carbon atoms in the following structure
GHW#1: #9 IUPAC name of the following branched alkane:
Reactions of alkanes Combustion CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) Many alkanes are used this way - as fuels Methane - natural gas Propane - used in gas grills Butane - lighters Gasoline - mixture of many hydrocarbons,
Halogenation Reactions of alkanes A reaction where a halogen replaces one or more hydrogens. CH 4 (g) + Cl 2 (g) Used to prepare many solvents dichloromethane - paint stripper chloroform heat or light CH 3 Cl(g) + HCl(g) - once used as anesthesia 1,2-dichloroethane - dry cleaning fluid
4. Complete combustion reaction of following alkanes. a) CH 4 b) C 4 H 10 c) C 5 H 12
Cycloalknes Cyclic alkanes: General molecular formula, C n H 2n 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
Cycloalkanes :saturated hydrocarbons with a carbon ring Have C-C single bonds in a ring structure. General formula C n H 2n cyclopropane cyclobutane
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.
Cycloalkanes Cycloalkanes have molecular formula C n H 2n 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. 20
Naming simple of cycloalkanes: cyclopropane cyclobutane cyclopentane cyclohexane cycloheptane cyclooctane
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. 60º 90º 108º 109.5º Least stable Most stable
Naming branched cycloalkanes Commonly written as line-angle formulas examples: Isopropylcyclopentan e 1-tert -Bu tyl-4-methylcycloh exane 1-Isobutyl-2-meth ylcyclohexan e 1-Ethyl-1-methylcyclopropane
5. IUPAC name of the following substituted cycloakane
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.
Disubstituted Cycloalkanes There are two different 1,2-dimethylcyclopentanes one having two CH 3 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. 26
Haloalkanes An alkane in which one or more H atoms is replaced with a halogen (F, Cl, Br, or I) CH 3 Br Br 1-bromomethane (methyl bromide) CH 3 CH 2 CHCH 3 2-bromobutane Cl chlorocyclobutane Timberlake LecturePLUS 1999 27
6. Give the common/iupac names of following substituted alkanes: Common IUPAC a) CH 2 Cl 2 b) CHCl 3 c) CCl 3 F e) CCl 2 F 2
7. Define following types of terms used in describing isomerism: a) Isomers: An example: b) Constitutional isomers: An example:
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.
Ethane Conformers Staggered conformer has lowest energy. Dihedral angle = 60 degrees H H Dihedral angle H H H H model Newman projection sawhorse
Ethane Conformers (2) Eclipsed conformer has highest energy Dihedral angle = 0 degrees =>
Conformational Analysis Torsional strain: resistance to rotation. For ethane, only 12.6 kj/mol =>
Stereoisomers c) Conformational stereroisomers: d) Geometric stereoisomers: e) Optical stereoisomers (d and l Enantiomers):
8) Describe the conformational isomerism in following alknes: a) Butane, C 4 H 10 : b) Cyclopenatane, C 5 H 10 : c) Cyclohexane C 6 H 12 :
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 C n H 2n+2 It relates molecular formula to possible structures
9. Calculate the units of unsaturation in following hydrocarbons a) Butane, C 4 H 10 : b) Cyclopenatane, C 5 H 10 : c) Ethene (ethylene), C 2 H 4 : d) Cyclohexa-1,3,5-triene (Benzene), C 6 H 6 :