Chapters 1, 2, & 3. CHAPTER 3 *** 3-D Molecular Model Set Needed*** Saturated Hydrocarbons (AKA: Alkanes) (AKA:Paraffins)

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1 Sevada Chamras, Ph.D. Glendale Community College Chemistry 105 Exam. 1 Lecture Notes Chapters 1, 2, & 3 CAPTER 3 *** 3-D Molecular Model Set Needed*** Saturated ydrocarbons (AKA: Alkanes) (AKA:Paraffins) 1. General Formula: 2. Functional Group or Side Chain : 2. General IUPAC Nomenclature for Alkanes: C's Molecular Formula! Name Functional GroupFormula! Name 1 C 4! C 3! 2!! 3!! 4!! 5!! 6!! 7!! 8!! 9!! 10!! 11!! 12!! 1

2 ***Note: Only 4 bonds are extended from carbons, and only 1 bond is extended from hydrogens. 3. Isomerism in ydrocarbons: n-alkanes: Constitutional isomers of n-alkanes: EXAMPLE: Methane: (1) Ethane: (1) Propane: (1) Butane: (2) Pentane: (3) exane: (5) ow many isomers? Is there a predicting formula? 2

3 4. IUPAC Nomenclature Steps and Rules for Alkanes: Locate the longest continuous chain! This will be used as the name of the base compound Example: ***What if there is more than 1 longest continuous chain? Example: Number the carbons in the main chain. ***Note: There are 2 ways (from 2 ends) of numbering the chain. Choose the end as the #1 carbon that is nearest to the substituent. 3

4 Indicate the location of the substituent(s) [side chain(s)]. When there is more than one side chain, the correct way for naming should have the side-chains mentioned by alphabetical order. When two or more of the side chains are the same, use numbering prefixes like di, tri, tetra, etc., in order to avoid repetition of the names for the side chains. Numbers are separated from each other with commas. Numbers are separated from letters with dashes. Types of Carbons Based on Substitution: 1. Methyl: 2. Primary: 3. Secondary: 4. Tertiary: 4

5 Some Common Side Chains: 3 C C 2 2 C 3 C C C 3 3 C 2 C C 2 2 C 3 C 2 C C C 3 3 C C 2 C 3 C C 3 C C 3 C 3 5

6 Examples for Naming More Complex Side Chains: 3 C C 2 C 3 C C VC 3 C 2 C C C 3 3 C C 3 C 3 Physical Properties of Alkanes: a) Solubility (Polarity): b) Average Density: c) Melting Point: What appens at Melting Point? 1. The Effect of Molar Mass: 6

7 2. The Odd-Even Carbon Effect: 3. The Effect of Branching: Structure & Conformation of Alkanes: 1. ybridization and Structure of Carbons in Alkanes: ybridization! Bonds! Geometry! Ideal Bond Angle 2. What is Conformation? 3. What is Free Rotation? 4. What is Conformational Isomer? (Conformer) 7

8 5. An Initial Look at Ethane and Its Two Possible Conformations: Molecular Formula:C 2 6 Condensed Formula: 3 CC 3 3-Dimensional Structural Formula: (AKA: Wedge-Dash) Bond-Line Formula: 3 C C 3 Expanded Structural Formula: C C ***Drawing 3-Dimensional (Wedge-Dash) Structures: (Use the model set now) Drawing Tools Wedge Line Dash a) Draw the carbon skeleton in the plane of the paper, showing the carbons: Ethane Propane 8

9 b) Add in the hydrogens using the wedges, the dashes, and the straight lines: Ethane Propane 6. Two Methods for Structure Drawing to Study Conformers More Effectively: a) Newman Projection: (Viewing the molecule along the C-C bond axis) Draw two possible Wedge-Dash structure for Ethane: Structure A Structure B Convert the Wedge-Dash to Newman Projection by looking at it through the C-C bond of ethane: (Construct the model and view it along the C-C axis) Structure A Structure B 9

10 Names for Structures (conformers) A and B, based on the relative orientations of the hydrogen atoms on the carbons: Structure A: Structure B: Energetic Relation between Eclipsed and Staggered Conformers: Reason for the Energetic Trend: Dihedral Angle (! ): Definition: b) Sawhorse Projection: Start with the Newman Projection for each conformer drawn above: In your mind (or using the model set now) rotate the molecule thus tilting it enough to be able to see the C-C bond: Draw what you see: Eclipsed Staggered 10

11 Conformational Analysis of Ethane: Study of the change in the potential energy of ethane as a function of rotation around C-C bond (change in the dihedral angle size): E 0 o 60 o 120 o 180 o Dihedral Angle ( o ) Conformational Analysis of Butane: E 0 o 60 o 120 o 180 o 240 o 300 o 360 o Dihedral Angle ( o ) New Words: Gauche Conformer: Anti Conformer: Tortional Strain (Tortional Energy): Steric Strain (Steric Energy): 11

12 General Formula: Cyclic Saturated ydrocarbons (AKA: Cycloalkanes) Naming Unsubstituted Cyclic Alkanes: Naming Substituted Cyclic Alkanes: 1. With one substituent: Similar to open-chain alkanes: Example: 2. With more than one substituent: 12

13 Number the ring carbons. The correct direction for numbering is the one that results in Example: the smallest numbers for the substituents: When the open chain contains more carbons than the ring, the open chain becomes the Example: main compound, and the ting becomes a substituent (side chain). 13

14 Conformations in Cycloalkanes: 1. Cyclopropane: An equilateral triangle (seemingly). Angles: 60 o vs. 72 o. Bent Bonds: Strengtth of the C-C bonds: 60 o Angle Strain: sp 3 angle = o, C-C-C angle in cyclopropane = 2. Cyclobutane: Flat vs. puckered ring: 3. Cyclopentane: Angle = 108 o Three conformations: Angles = 90 o o >Angles > 90 o Planar Envelope alf-chair More torsional Less Torsional Less Torsional Strain Strain Strain 14

15 4. Cyclohexane: Virtually free of torsional and angle strain. Conformations: Chair, boat, twist-boat. a) Drawing the carbon skeleton: 1. Draw 2 parallel lines as shown: Drawing the Chair Conformer 2. Draw another set of two parallel lines stemming from the end of one and the beginning of the other line: 3. Connect the two bent shapes to complete the carbon skeleton of the ring: b) Drawing in the substituents (hydrogens in case of an unsubstituted cyclohexane): 1. The axial substituents are drawn as vertical lines pointing above and below the plane of the ring in an alternating fashion. int: Start with the higher tip of the ring and have the substituent pointing above the plane of the ring. 15

16 2. The equatorial substituents are drawn as tilted straight lines pointing above and below the plane of the ring, and directed away from the body of the ring. If the axial substituent points above the plane, then the axial should point below, and vice versa. *int: To get a better, more precise idea on the exact direction of the equatorial substituents, 4 of the 6 equatorial substituents are parallel to 4 C-C bonds of the ring. The picture below illustrated the corresponding parallel pairs: Conformation Conversions in Cyclohexane: Chair 1 "! alf-chair 1 "! Twist Boat "! alf-chair 2 "! Chair 2 Energetic comparison of the conformers:.chairs:.alf-chairs:.twist Boat: E Boat 16

17 ,3-Diaxial Interaction: 5 4 Flipping Chairs! Substituted Cyclohexanes: Equilibrium between the chair forms of mono-substituted cyclohexanes: 17

18 Disubstituted Cyclohexanes: Cis & trans Substituents: Cis- Trans- 1. 1,2 substitution: 2. 1,3 substitution: 3. 1,4 substitution: Examples of disubstituted cyclohexanes and the equilibria for the chair conformers. 18

19 Bicyclic Compounds: Compounds containing 2 joined rings. Types: 1. Brigded 2. Fused EXAMPLES 3. Spirocyclic Nomenclature: Example: a) For Bridged and Fused: Locate the bridgehead. Count the number of carbons in each bridge, excluding the bridgehead carbons. Start with the prefix bicyclo Follow with the bridge count in decreasing order of carbons. List the name of the alkane matching the total number of carbons in the bicyclic compound. b) For Spirocyclics: Start with the prefix spiro Count the carbons of the two tethered portions joined at one point, excluding the spiro carbon. Follow with the tether count in decreasing order of carbons. List the name of the alkane matching the total number of carbons in the spiro compound. 19

20 Example: 20