Deduce a possible structure for the compound with the IR absorptions below. C3H5N: 3000, 2250 cm-1 * Deduce a possible structure for the compound with the IR absorptions below. C5H8O: 3000, 1750 cm-1 * Physical Properties Chemical Shape and Bonding September 7, 2010 Chapters 1 and 2 * * Alkanes are hydrocarbons containing only single bonds General formula: CnH2n+2 * * The greater the attractive forces between molecules, the higher is the boiling point of the compound. Attractive Forces van der Waals force Dipole?dipole interaction Hydrogen bonds * van der Waals Forces The boiling point of a compound increases with the increase in van der Waals force * Dipole?Dipole Interaction Dipole?dipole interactions are stronger than van der Waals force but weaker than ionic or covalent bonds * A Polar Bond Has a Dipole Moment A polar bond has a negative end and a positive end dipole moment (D) = m = e x d (e) : magnitude of the charge on the atom (d) : distance between the two charges * The vector sum of the magnitude and the direction of the individual bond dipole determines the overall dipole moment of a molecule Molecular Dipole Moment * * Hydrogen bonds are stronger than other dipole-dipole interactions and van der Waals force * Which of the compounds below will form hydrogen bonds between its molecules? A) CH3CH2CH2F B) CH3CH2CH2CH3 C) (CH3)3N D) CH3CH2OCH3 E) CH3NHCH2CH3 * * Both van der Waals and dipole-dipole interactions must be overcome for an alkyl halide to boil Which of the following will have the lowest boiling point? A) CH3Cl B) CH4 C) CH2Cl2 D) CHCl3 E) CCl4 * Which of the molecules below has the higher boiling point? CH3CH2CH2OH or CH3CH2OCH3 * * The melting point is influenced by the packing of the molecules in the crystal lattice * Like Dissolves Like Polar compound dissolves in polar solvent Nonpolar compound dissolves in nonpolar solvent * ?Like Dissolves Like? Concept Important in Drug Action Crossing the Blood-Brain Barrier requires a fat-soluble drug. THC and Barbiturates possess hydrocarbon tails to facilitate crossing this barrier. Hydrocarbon substituents are termed ?lipophilic? or fat-loving. Substituents that possess hydrogen-bonding capability are termed ?hydrophilic?or water-loving. Which of the following has the greatest solubility in CH3CH2CH2CH3? A) CH3OH B) CH3O- Na+ C) CH3NH2 D) CH3OCH3 E) (CH3)3CH * Which of the following is the most soluble in H2O? A) CH3OCH3 B) CH3CH2OH C) CH3CH2Cl D) CH3CH2CH3 E) CH3CHO * Chemical Shape and Bonding * * Molecular Orbitals Molecular orbitals belong to the whole molecule. s bond: formed by overlapping of two s orbitals. Bond strength/bond dissociation: energy required to break a bond or energy released to form a bond. * * In-phase overlap forms a bonding MO; out-of-phase overlap forms an antibonding MO: * Sigma bond (s) is formed by end-on overlap of two p orbitals: A s bond is stronger than a p bond * Pi bond (p) is formed by sideways overlap of two parallel p orbitals: What kind of molecular orbital (?, ?*, ?, or ?*) results when the two atomic orbitals shown below interact in the manner indicated? * What kind of molecular orbital (?, ?*, ?, or ?*) results when the two atomic orbitals shown below interact in the manner indicated? * * Bonding in Methane * Hybridization of One s and Three p Orbitals * The orbitals used in bond formation determine the bond angles Tetrahedral bond angle: 109.5° Electron pairs spread themselves into space as far from each other as possible * The Bonds in Ethane * Hybrid Orbitals of Ethane Choose the correct hybridization for the atom indicated in the molecule below CH3CH2CH2CH3 ? A) sp B) sp2 C) sp3 D) none of the above *
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