1 Organic Chemistry, Third Edition Janice Gorzynski Smith University of Hawai’i Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 4 Lecture Outline Prepared by Layne A. Morsch The University of Illinois - Springfield

2 1. Alkanes (only C-C and C-H  bonds). 1) Acyclic alkanes (saturated hydrocarbons): C n H 2n+2 linear and branched chains. 2) Cyclic, Cycloalkanes: one or more rings. C n H 2n, Acyclic Alkanes and Cycloalkanes 2. sp 3 hybridized (tetrahedral geometry, 109.5°).

3 1. Molecular formula C 3 H 8. Propane (C 3 ) 2. Equivalent representation of propane: horizontal row or bend

4 1. Constitutional isomers (structural isomers) — 1) Different compounds with the same molecular formula. 2) Different connectivity. Ex) C 4 H 10, butane & isobutane. Constitutional Isomers

5 Primary (1 o ) C & H Secondary (2 o ) C & H Tertiary (3 o ) C & H Quaternary (4 o ) C & H Classification of Carbon & Hydrogen

6 The suffix “-ane” : alkanes. Naming Alkanes

7 C n H 2n adding the prefix cyclo- to the name of the acyclic alkane Cycloalkanes

Nomenclature 1.Common name: traditionally given long ago 2.Systematic name: IUPAC system 3.Others 1) Generic name: officially approved name for drug 2) Trade name: assigned by company or manufacturer 8

9 1.The parent name: the longest continuous carbon chain (main chain). 2.The suffix: functional group. 3.The prefix: the identity, location, and number of substituents. Nomenclature

10 Carbon substituents bonded to the main chain. Naming an alkyl group: –ane  –yl. ex) methane (CH 4 )  methyl (CH 3 -) ethane (CH 3 CH 3 )  ethyl (CH 3 CH 2 -). Alkyl Groups (R-)

11 Propane (C3) has both 1° and 2° H atoms, 1) removal of 1° atom  propyl. 2) removal of 2° atom  isopropyl Naming C 3 Alkyl Groups

12 Step [1] Find the parent chain (main chain). straight or bend ? The IUPAC System

13 The main chain has the greater number of substituents. Structures with Chains of Equal Length

14 Step [2] with Substituents 1) the lowest possible number for the substituents.

15 2) Substituents in alphabetical order. Alphabetize, by ignoring all prefixes except iso (isopropyl & isobutyl).

16 Step [3] two or more identical substituents. use prefixes : di-, tri-, tetra-.

17 Step [4] Substituent number & name + parent + suffix. Completing Structure Names

18 Add the prefix cyclo- to the parent. Step [1] Find the parent cycloalkane. Naming Cycloalkanes Using the IUPAC System

19 Step [2] For rings with two or more substituent, give the lowest substituent number & alphabetical order. Numbering Substituents in Cycloalkanes

20 Naming Alkanes vs. Cycloalkanes C # in the ring ≥ C # in the chain: named as cycloalkane. C # in the ring < C # in the chain: named as alkane.

21 Figure 4.3 Examples of Naming Cycloalkanes

22 Some are identified using common names (not IUPAC system). Named long ago before the IUPAC system. Some are descriptive of shape and structure. Common Names of Polycyclic Molecules

23 Natural gas: largely C 1, with lesser amounts of C 2 ~ C 4. Petroleum: C 1 ~ C 40. Alkanes in Fossil Fuels

24 Refining crude petroleum. (a) An oil refinery. (b) Schematic of a refinery tower. Refining of Oil Distilling crude petroleum (refining). gasoline: C 5 H 12 —C 12 H 26 kerosene: C 12 H 26 —C 16 H 34 diesel fuel: C 15 H 32 —C 18 H 38

Physical Properties of Alkanes Alkanes: only van der Walls force 1) Phase: C1 ~ C4 : gas C5 ~ C18 : liquid C19 ~ : solid 2) bp: cycle- > n-alkane > branched alkane (packing effect & surface area) 3) mp: C 2n > C 2n+1 (symmetry  packing effect) 4) Density & solubility: the lowest density in all org. compds. soluble in non-polar solvents 25

26 Alkane Boiling Points

27 Alkane Melting Points

28 Conformations: different spatial arrahgement (  bond rotation), interconvertible. cf) Configuration: different bond connectivity. Conformations of Acyclic Alkanes

29 Eclipsed conformation: the C-H bonds are aligned. Staggered conformation: the C-H bonds staggered Conformational Analysis: Eclipsed and Staggered Conformations

30 Rotation of a bond by 60° : eclipsed conformation staggered conformation. For ethane, the dihedral angle for the staggered conformation is 60°; for eclipsed is 0°. Conformations and Dihedral Angle

31 Newman projection: End-on representations for conformations. Step [1] Look directly down the C-C bond (end-on). HOW TO Draw a Newman Projection Step 2. Draw in the bonds. Step 3. Add the atoms on each bond.

32 Figure 4.6 Newman Projections - Ethane

33 The eclipsed conformations are less stable (higher in energy)  Electron-electron repulsion Conformations of Ethane

34 Torsional energy: The energy difference between staggered and eclipsed conformers 1) ~3 kcal/mol of ethane 2) each eclipsed C-H bond  1 kcal/mol. Torsional Energy of Ethane

35 Newman Projections - Propane Newman Projections - Butane 6 conformations of butane

36 1) Anti: A staggered conformation with two larger groups 180°. 2) Gauche : A staggered conformation with two larger groups 60° Anti and Gauche Conformations Conformational strains in alkane: 1) Tortional strain: instability due to the eclipsed conformation 2) Steric strain: Repulsice van der Waals force (too closeness of groups).

37 Figure 4.10 Conformation and Energy of Butane

38 The energy difference between the lowest and highest energy conformations is called barrier to rotation. Barrier to Rotation The lowest energy conformation  Zigzag Structure

Strains in Cycloalkanes Ring Strains 1 ) Tortional strain 2) Steric strain 3) Angle strain : Compression of internal bond angle in C-C bond.  distort their shapes to reduce angle and tortional strain. 39

40 Figure 4.11 Angle strain of Cycloalkanes (C 3 -C 10 ) Distortion of shapes to reduce angle and torsional strain.

41 Cyclohexane adopts a puckered “chair” conformation: No angle strain & torsional strain. Conformation of Cyclohexane

42 Drawing Cyclohexanes

43 Drawing Hydrogens on Cyclohexanes

44 Cyclohexane undergoes a conformational change called “ring- flipping.” Conformational Change – Ring-Flipping The equatorial position has more room than the axial position

45 The boat form : unstable by 7 kcal/mol than the chair form: 1) torsional strain (eclipsed conf.). 2) “flag pole” interaction of hydrogens (too close to each other). Boat Conformation of Cyclohexane

46 Drawing Substituted Cyclohexanes Larger group in equatorial position

47 Preference of Equatorial Position in Substituted Cyclohexanes Larger axial substituents create destabilizing (and thus unfavorable) 1,3- diaxial interactions.

48 Ex) a very large substituent like tert-butyl [(CH 3 ) 3 C-]  equatorial. Preference of Equatorial Position in Substituted Cyclohexanes

49 1,2-dimethylcyclopentane: 2 different orientations in space. Cis and Trans Stereoisomers of Disubstituted Cycloalkanes

50 Ex) trans- & cis-1,4-dimethylcyclo-hexane Disubstituted Cycloalkanes Ex) trans-1,4-dimethylcyclo-hexane

51 Ex) cis-1,4-dimethylcyclo-hexane  axial & equatorial.

52 An oxidation-reduction reaction. Combustion of Alkanes

53 1. Oxidation: Increase in C-Z bonds or decrease in C-H bonds. 2. Reduction: Decrease in C-Z bonds or increase in C-H bonds. Oxidation and Reduction Reactions

54 Lipids: Soluble in organic solvents and insoluble in water. Nonpolar C-H and C-C bonds & polar functional groups. Figure 4.20 Three representative lipid molecules Lipids

55 A steroid family 1) Insoluble in H 2 O 2) Embedded in a lipid bilayer of a cell membrane Cholesterol