Chapter 2 Structure and Properties of Organic Molecules Organic Chemistry, 5 th Edition L. G. Wade, Jr. Jo Blackburn Richland College, Dallas, TX Dallas County Community College District 2003, Prentice Hall
Chapter 22 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 23 Wave Interactions Linear combination of atomic orbitals between different atoms is bond formation on the same atom is hybridization. Conservation of orbitals Waves that are in phase add together. Amplitude increases. Waves that are out of phase cancel out. =>
Chapter 24 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 25 H 2 : s-s overlap =>
Chapter 26 Cl 2 : p-p overlap => Constructive overlap along the same axis forms a sigma bond.
Chapter 27 HCl: s-p overlap Question: Draw the predicted shape for the bonding molecular orbital and the antibonding molecular orbital of the HCl molecule. Answer: See bottom of page 42 in your text. =>
Chapter 28 Pi Bonding Pi bonds form after sigma bonds. Sideways overlap of parallel p orbitals. =>
Chapter 29 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 210 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 211 sp Hybrid Orbitals 2 VSEPR pairs Linear electron pair geometry 180° bond angle =>
Chapter 212 sp 2 Hybrid Orbitals 3 VSEPR pairs Trigonal planar e - pair geometry 120° bond angle =>
Chapter 213 sp 3 Hybrid Orbitals 4 VSEPR pairs Tetrahedral e - pair geometry 109.5° bond angle =>
Chapter 214 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! NH 2 CH 3 -C C-CHO =>
Chapter 215 Rotation around Bonds Single bonds freely rotate. Double bonds cannot rotate unless the bond is broken. =>
Chapter 216 Isomerism Molecules which have the same molecular formula, but differ in the arrangement of their atoms, are called isomers. Constitutional (or structural) isomers differ in their bonding sequence. Stereoisomers differ only in the arrangement of the atoms in space. =>
Chapter 217 Structural Isomers =>
Chapter 218 Stereoisomers Cis - same side Trans - across Cis-trans isomers are also called geometric isomers. There must be two different groups on the sp 2 carbon. No cis-trans isomers possible =>
Chapter 219 Bond Dipole Moments are due to differences in electronegativity. depend on the amount of charge and distance of separation. In debyes, x (electron charge) x d(angstroms) =>
Chapter 220 Molecular Dipole Moments Depend on bond polarity and bond angles. Vector sum of the bond dipole moments. Lone pairs of electrons contribute to the dipole moment. =>
Chapter 221 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 222 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 223 Dipole-Dipole =>
Chapter 224 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 225 Dispersions =>
Chapter 226 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 227 H Bonds =>
Chapter 228 Boiling Points and Intermolecular Forces =>
Chapter 229 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 230 Ionic Solute with Polar Solvent Hydration releases energy. Entropy increases. =>
Chapter 231 Ionic Solute with Nonpolar Solvent =>
Chapter 232 Nonpolar Solute with Nonpolar Solvent =>
Chapter 233 Nonpolar Solute with Polar Solvent =>
Chapter 234 Classes of Compounds Classification based on functional group Three broad classes Hydrocarbons Compounds containing oxygen Compounds containing nitrogen =>
Chapter 235 Hydrocarbons Alkane: single bonds, sp 3 carbons Cycloalkane: carbons form a ring Alkene: double bond, sp 2 carbons Cycloalkene: double bond in ring Alkyne: triple bond, sp carbons Aromatic: contains a benzene ring =>
Chapter 236 Compounds Containing Oxygen Alcohol: R-OH Ether: R-O-R ' Aldehyde: RCHO Ketone: RCOR ' =>
Chapter 237 Carboxylic Acids and Their Derivatives Carboxylic Acid: RCOOH Acid Chloride: RCOCl Ester: RCOOR ' Amide: RCONH 2 =>
Chapter 238 Compounds Containing Nitrogen Amines: RNH 2, RNHR ', or R 3 N Amides: RCONH 2, RCONHR, RCONR 2 Nitrile: RCN =>
Chapter 239 End of Chapter 2