Chapter 2: Structure and Properties of Organic Molecules, continued

Chapter 2: Structure and Properties of Organic Molecules, continued PowerPoint PPT Presentation

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Chapter 2: Structure and Properties of Organic Molecules, continued

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1. Chapter 2: Structure and Properties of Organic Molecules, continued Molecular polarity Intermolecular forces and physical properties Isomerism Functional groups

2. Bond Dipole Moments Due to differences in electronegativity

3. Molecular Dipole Moment Overall electron distribution within a molecule Depends on bond polarity and bond angles Vector sum of the bond dipole moments Lone pairs of electrons contribute to the dipole moment Consider both magnitude and direction of individual bond dipole moments Symmetrical molecules with polar bonds = nonpolar

4. Intermolecular Forces Strength of attractions between molecules Influence physical properties (bp, solubility) Classification depends on structure Molecular polarity Dipole-dipole interactions Hydrogen bonding London dispersions (van der Waals)

5. Dipole-Dipole Forces Between polar molecules Positive end of one molecule aligns with negative end of another molecule Lower energy than repulsions Larger dipoles cause higher boiling points

6. Hydrogen Bonding Strongest dipole-dipole attraction H-bonded molecules have higher boiling points 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

7. London Dispersion Forces van der Waals forces Between all molecules important with nonpolar compounds Temporary dipole-dipole interactions Molecules with more surface area have stronger dispersion forces and higher boiling points Larger molecules Unbranched molecules

8. Boiling Points and Intermolecular Forces

9. Solubility and Intermolecular Forces Like dissolves like Polar solutes dissolve in polar solvents Nonpolar solutes dissolve in nonpolar solvents Molecules with similar intermolecular forces will mix freely

10. Ionic Solute with Polar Solvent

11. Ionic Solute with Nonpolar Solvent

12. Nonpolar Solute with Nonpolar Solvent

13. Nonpolar Solute with Polar Solvent

14. Isomers Molecules with the same molecular formula, but different arrangements of atoms Constitutional (structural) isomers Differ in their connectivity Stereoisomers Differ only in the spatial arrangement/orientation of their atoms

15. Structural Isomers

16. Stereoisomers Cis-trans isomers are also called geometric isomers There must be two different groups on the sp2 carbon

17. Classes of Compounds Classification based on functional group Collection of atoms at a site within a molecule with a common bonding pattern Reacts in a typical way, generally independent of the rest of the molecule Three broad classes Hydrocarbons Compounds containing oxygen Compounds containing nitrogen

18. 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

19. Compounds Containing Oxygen Alcohol: R-OH Ether: R-O-R' Aldehyde: RCHO Ketone: RCOR'

20. Carboxylic Acids and Their Derivatives Carboxylic Acid: RCOOH Acid Chloride: RCOCl Ester: RCOOR' Amide: RCONH2

21. Compounds Containing Nitrogen Amines: RNH2, RNHR', or R3N Amides: RCONH2, RCONHR, RCONR2 Nitrile: RCN

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