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Alkanes: Structure and Conformation. Compounds Contain Only C, H General Formula: C n H 2n+2 (Saturated) Common Source of Alkanes: Petroleum Separation Technique: Fractional Distillation Boiling Point (Size) Method of Separating Basic Building Block of More Complex Organics.

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alkanes structure and conformation
Alkanes: Structure and Conformation
  • Compounds Contain Only C, H
    • General Formula: CnH2n+2 (Saturated)
  • Common Source of Alkanes: Petroleum
  • Separation Technique: Fractional Distillation
  • Boiling Point (Size) Method of Separating
  • Basic Building Block of More Complex Organics
alkane shape straight chains
Alkane Shape: Straight Chains
  • “Straight Chain” Better Termed “Unbranched”
  • Actually Zig-Zag Structures (Tetrahedral Carbon Atoms)
  • All Carbons sp3 Hybridized
branched alkanes simple
Branched Alkanes: Simple
  • Constitutional Isomers: Same Formula; Different Connectivity
    • Butane and Isobutane: C4H10
    • Pentane, Isopentane, Neopentane: C5H12
    • Different Properties: BP, MP, Density, Refractive Index etc.
    • Number of Constitutional Isomers Increases w/ # of Carbons
alkyl group nomenclature
Alkyl Group Nomenclature

Unbranched Alkyl Groups

branched alkanes
Branched Alkanes
  • Locate Longest Continuous Chain (Parent Name)
  • Number Carbons in Chain; Begin @ End Nearest Substituent
  • Use Number of C on Parent Chain; Locate Substituents
  • Assign C Number to Each Substituent
  • Use Same C Number If Multiple Substituents
  • If Substituents Identical, Use Di-, Tri-, Tetra- Designations
  • Equal Length Chains Compete, Parent Chain Most Substituted
  • First Branches Equivalent; Choose Lowest Possible # Set
branched alkanes examples8
Branched Alkanes: Examples
  • Once Long Chain Found; Simplify w/ Alkyl Abbreviations
branched alkyl groups
Branched Alkyl Groups
  • Can Name as Simple Alkane w/ “yl” Ending Replacing “ane”
alkyl halides
Alkyl Halides
  • Alkyl Halides Named as “Halo”-Alkane
    • “Halo” = Fluoro, Chloro, Bromo, Iodo
alcohols
Alcohols
  • Note the “-ol” Ending
  • Use Same Di-, Tri-, Tetra- to Indicate Multiple
  • We’ll Designate Alcohols as Priority Groups (Give Low #)
monocyclic alkanes alcohols
Monocyclic Alkanes/Alcohols

Lowest Number

Set

  • “Cyclo” Added  Indicates Cyclic Structure
terminal alkenes
Terminal Alkenes

Feature an “ene” Ending

properties of alkanes
Properties of Alkanes
  • Boiling Point Increases Regularly for Unbranched
  • Branching Lowers Boiling Points (Van der Waals, SA)
  • Melting Point in Unbranched Increases Regularly Within
  • ODD or EVEN Numbered Series (Not Both)
  • Density Less Than 1.0 g/mL (Less Than H2O)
  • Solubility: Quite Insoluble in H2O; Less Dense  Float
    • Non Polar (Like Dissolves Like)
    • No Hydrogen Bonding
sigma bonds in hydrocarbons
Sigma Bonds in Hydrocarbons
  • Alkane Sigma (s) Bonds Formed From sp3 Hybridized C
  • These Bonds Can Freely Rotate
  • Temporary Shapes Adapted via Rotation: CONFORMERS
  • Conformers can have Different Energies
  • Need to Have a System for Depicting Various Conformations
    • Newman Projections
    • Sawhorse Formulas
newman projections sawhorse formula
Newman Projections/Sawhorse Formula
  • R Groups 180° Apart (Anti Conformation)
  • 4 Atom Angle (3 Bond Angle) is a Dihedral (Torsional) Angle
  • Having Large Groups Anti is Low in Energy
newman projections sawhorse formula20
Newman Projections/Sawhorse Formula
  • When R Groups 0° Apart (Ecclipsed Conformation)
  • Having Large Groups Anti is High in Energy
  • Can Adapt any Range of Conformations in Between
conformational analysis butane
Conformational Analysis: Butane

Energy

  • Can Plot these Points and Connect w/ Curve: PES
cyclohexane conformation
Cyclohexane Conformation
  • Cyclohexanes Adapt Chair Conformations (Boats and Others)
  • Ax: Axial (Straight up and Down on Chair)
  • Eq: Equatorial (Parallel to Next Bonds over in Chair)
cyclohexane conformation cis
Cyclohexane Conformation: Cis
  • Methyls are Cis (Same); Two Energy Equivalent Chairs
  • Ring Flips Interchange Chair Conformations
cyclohexane conformation trans
Cyclohexane Conformation: Trans
  • Methyls are Cis (Same); Two Energy Inequivalent Chairs
  • Diequatorial Much More Stable than Diaxial Conformation
cyclohexane conformation notes
Cyclohexane Conformation: Notes
  • With Multiple Same Substituents; More Equatorial = Better
  • Larger Groups Tend to Adopt Equatorial Positions
  • tert-butyl Groups Nearly Always Equatorial
    • Conformation Setters (Lock Ring)
    • Set Other Groups Relative to tert-butyl
  • Fused Rings (Decalin, for Example) Can be Drawn as Chairs
reactions hydrogenation
Reactions: Hydrogenation
  • Addition of Hydrogen (H2) Across a Multiple (p) Bond
  • Ethanol (CH3CH2OH) is a Common Solvent
reactions alkyl halide reducation
Reactions: Alkyl Halide Reducation
  • Zn Transfers Electrons to C of Alkyl Halide
  • Alkyl Halide is Reduced (Reduction = Gains Electrons)
  • Zn: Good Two Electron Donor (Reductant, Reducing Agent)
reactions alkylation of terminal alkynes
Reactions: Alkylation of Terminal Alkynes
  • NaNH2 (-NH2) to Deprotonate Alkyne (Acid/Base Reaction)
  • Anion Reacts with Alkyl Halide (Bromide); Displaces Halide
  • Alkyl Group Added to Alkyne
  • Alkyl Halide Must be 1° or Me; No Branching at 2nd (b) Carbon
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