1 / 43

Chapter 2 Structure and Properties of Organic Molecules

Organic Chemistry , 6 th Edition L. G. Wade, Jr. Chapter 2 Structure and Properties of Organic Molecules. Jo Blackburn Richland College, Dallas, TX Dallas County Community College District ã 2006, Prentice Hall. =>. Wave Properties of Electrons. Standing wave vibrates in fixed location.

landen
Download Presentation

Chapter 2 Structure and Properties of Organic Molecules

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Organic Chemistry, 6th EditionL. G. Wade, Jr. Chapter 2Structure and Propertiesof Organic Molecules Jo Blackburn Richland College, Dallas, TX Dallas County Community College District ã 2006,Prentice Hall

  2. => Wave Properties of Electrons • Standing wave vibrates in fixed location. • Wave function, , mathematical description of size, shape, orientation. • Amplitude may be positive or negative. • Node: amplitude is zero. Chapter 2

  3. Wave Interactions • Linear combination of atomic orbitals • on different atoms produce molecular orbitals • on the same atom give hybrid orbitals. • Conservation of orbitals. • Waves that are in phase add together.Amplitude increases. • Waves that are out of phase cancel out. => Chapter 2

  4. => Bonding Region • Electrons are close to both nuclei. Chapter 2

  5. Sigma Bonding • Electron density lies between the nuclei. • A bond may be formed by s-s, p-p, s-p, or hybridized orbital overlaps. • The bonding MO is lower in energy than the original atomic orbitals. • The antibonding MO is higher in energy than the atomic orbitals. => Chapter 2

  6. Bonding Molecular Orbital Two hydrogens, 1s constructive overlap => Chapter 2

  7. Anti-Bonding Molecular Orbital Two hydrogens, destructive overlap. => Chapter 2

  8. H2: s-s overlap => Chapter 2

  9. Cl2: p-p overlap Constructive overlap along the same axis forms a sigma bond. => Chapter 2

  10. => HCl: s-p overlap Question: What is the predicted shape for the bonding MO and the antibonding MO of the HCl molecule? Chapter 2

  11. => Pi Bonding • Pi bonds form after sigma bonds. • Sideways overlap of parallel p orbitals. Chapter 2

  12. => Multiple Bonds • A double bond (2 pairs of shared electrons) consists of a sigma bond and a pi bond. • A triple bond (3 pairs of shared electrons) consists of a sigma bond and two pi bonds. Chapter 2

  13. Molecular Shapes • Bond angles cannot be explained with simple s and p orbitals. Use VSEPR theory. • Hybridized orbitals are lower in energy because electron pairs are farther apart. • Hybridization is LCAO within one atom, just prior to bonding. => Chapter 2

  14. => sp Hybrid Orbitals • 2 VSEPR pairs • Linear electron pair geometry • 180° bond angle Chapter 2

  15. => sp2 Hybrid Orbitals • 3 VSEPR pairs • Trigonal planar e- pair geometry • 120° bond angle Chapter 2

  16. => sp3 Hybrid Orbitals • 4 VSEPR pairs • Tetrahedral e- pair geometry • 109.5° bond angle Chapter 2

  17. => Sample Problems • Predict the hybridization, geometry,and bond angle for each atom in the following molecules: • Caution! You must start with a good Lewis structure! • NH2NH2 • CH3-CC-CHO Chapter 2

  18. => Rotation around Bonds • Single bonds freely rotate. • Double bonds cannot rotate unless the bond is broken. Chapter 2

  19. Isomerism • Same molecular formula, but different arrangement of atoms: isomers. • Constitutional (or structural) isomers differ in their bonding sequence. • Stereoisomers differ only in the arrangement of the atoms in space. => Chapter 2

  20. => Structural Isomers Chapter 2

  21. Trans - across Cis - same side No cis-trans isomers possible => Stereoisomers Cis-trans isomers are also called geometric isomers. There must be two different groups on the sp2 carbon. Chapter 2

  22. are due to differences in electronegativity. depend on the amount of charge and distance of separation. In debyes,  = 4.8 x (electron charge) x d(angstroms) => Bond Dipole Moments Chapter 2

  23. => Molecular Dipole Moments • Depend on bond polarity and bond angles. • Vector sum of the bond dipole moments. Chapter 2

  24. Effect of Lone Pairs Lone pairs of electrons contribute to the dipole moment. => Chapter 2

  25. Intermolecular Forces • Strength of attractions between molecules influence m.p., b.p., and solubility, esp. for solids and liquids. • Classification depends on structure. • Dipole-dipole interactions • London dispersions • Hydrogen bonding => Chapter 2

  26. Dipole-Dipole Forces • Between polar molecules. • Positive end of one molecule aligns with negative end of another molecule. • Lower energy than repulsions, so net force is attractive. • Larger dipoles cause higher boiling points and higher heats of vaporization. => Chapter 2

  27. Dipole-Dipole => Chapter 2

  28. => London Dispersions • Between nonpolar molecules • Temporary dipole-dipole interactions • Larger atoms are more polarizable. • Branching lowers b.p. because of decreased surface contact between molecules. Chapter 2

  29. Dispersions => Chapter 2

  30. Hydrogen Bonding • Strong dipole-dipole attraction. • Organic molecule must have N-H or O-H. • The hydrogen from one molecule is strongly attracted to a lone pair of electrons on the other molecule. • O-H more polar than N-H, so stronger hydrogen bonding. => Chapter 2

  31. H Bonds => Chapter 2

  32. ethanol, b.p. = 78° C ethyl amine, b.p. = 17 ° C Boiling Points and Intermolecular Forces Chapter 2

  33. Solubility • Like dissolves like. • Polar solutes dissolve in polar solvents. • Nonpolar solutes dissolve in nonpolar solvents. • Molecules with similar intermolecular forces will mix freely. => Chapter 2

  34. Ionic Solute with Polar Solvent Hydration releases energy. Entropy increases. => Chapter 2

  35. Ionic Solute withNonpolar Solvent => Chapter 2

  36. Nonpolar Solute withNonpolar Solvent => Chapter 2

  37. Nonpolar Solute with Polar Solvent => Chapter 2

  38. Classes of Compounds • Classification based on functional group. • Three broad classes • Hydrocarbons • Compounds containing oxygen • Compounds containing nitrogen. => Chapter 2

  39. Hydrocarbons • Alkane: single bonds, sp3 carbons • Cycloalkane: carbons form a ring • Alkene: double bond, sp2 carbons • Cycloalkene: double bond in ring • Alkyne: triple bond, sp carbons • Aromatic: contains a benzene ring => Chapter 2

  40. => Compounds Containing Oxygen • Alcohol: R-OH • Ether: R-O-R' • Aldehyde: RCHO • Ketone: RCOR' Chapter 2

  41. => Carboxylic Acids and Their Derivatives • Carboxylic Acid: RCOOH • Acid Chloride: RCOCl • Ester: RCOOR' • Amide: RCONH2 Chapter 2

  42. => Compounds Containing Nitrogen • Amines: RNH2, RNHR', or R3N • Amides: RCONH2, RCONHR, RCONR2 • Nitrile: RCN Chapter 2

  43. End of Chapter 2 Chapter 2

More Related