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Chemistry 121(001) Winter 2016

This course provides an introduction to the fundamental concepts of organic chemistry and biochemistry. Topics covered include isomerism, functional groups, stereochemistry, reactions of alkanes and cycloalkanes. The course also covers the nomenclature and properties of organic compounds.

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Chemistry 121(001) Winter 2016

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  1. Introduction to Organic Chemistry and Biochemistry Instructor Dr. UpaliSiriwardane (Ph.D. Ohio State) E-mail: upali@latech.edu Office: 311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours: MTW 8:00 - 10:00 am; ThF9:00 - 10:00 am 1:00 - 2:00 pm. Chemistry 121(001) Winter 2016 December 18, 2015: Test 1 (Chapters 12-13) January 25, 2016:Test 2 (Chapters 14-16) February 17,2016:Test 3 (Chapters 17-19) February 29, 2016:Test 4 (Chapters 20-22) March 1, 2016: Make Up Exam: Chapters 12-22) Bring Scantron Sheet 882-E

  2. GHW Questions GHW#2

  3. Chapter 12. Saturated Hydrocarbons

  4. 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

  5. ConstitutionalIsomers Skeletal (Chp. 12) Functional (Chp. 14) Positional(Chp. 12) Stereoisomers Geometric (Chp. 13) Conformational (Chp.12) Enantiomers (Optical)(Chp. 16)

  6. 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

  7. Constitutional Isomers of Alkanes (CnH2n+2)

  8. 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 _________

  9. 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:

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

  11. 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 =

  12. Identify the type of carbon atoms • in the following structure

  13. GHW#1: #9 IUPAC name of the following branched alkane:

  14. 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,

  15. Reactions of alkanes Halogenation • 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

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

  17. 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

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

  19. 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.

  20. 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.

  21. Naming simple of cycloalkanes:

  22. 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

  23. Naming branched cycloalkanes Commonly written as line-angle formulas examples:

  24. IUPAC name of the following • substituted cycloakane

  25. 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.

  26. 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.

  27. 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

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

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

  30. 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.

  31. H H H H H Newman projection sawhorse H model Ethane Conformers Staggered conformer has lowest energy. Dihedral angle = 60 degrees Dihedral angle

  32. => Ethane Conformers (2) Eclipsed conformer has highest energy Dihedral angle = 0 degrees

  33. => Conformational Analysis • Torsional strain: resistance to rotation. • For ethane, only 12.6 kJ/mol eclipsed staggered

  34. Conformational Analysis Butane

  35. Conformational Analysis Butane

  36. Stereoisomers c) Conformational stereroisomers: d) Geometric stereoisomers: e) Optical stereoisomers (d and l Enantiomers):

  37. 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.

  38. 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)

  39. 8) Describe the conformational isomerism in following alkanes: a) Butane, C4H10: b) Cyclopenatane, C5H10: c) Cyclohexane C6H12:

  40. 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

  41. 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:

  42. 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

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