Unit 1 – Organic Chemistry

1. Unit 1 – Organic Chemistry The properties and characteristics of organic compounds

2. Intermolecular forces • The physical and chemical properties are determined by the bonds and forces between atoms and molecules. • Intramolecular forces occur between atoms in molecules and determine a substance’s chemical properties. • Intermolecular forces occur between molecules and affect a substance’s physical properties.

3. Intermolecular forces • The physical properties of organic compounds are affected by the intermolecular forces of attraction and repulsion between molecules • Larger forces of intermolecular attraction result in high boiling & melting points. • Weak intermolecular forces result in low boiling & melting points producing gas states.

4. Intermolecular forces • The foundation for these intermolecular forces lies in the types of bonds that form between atoms in molecules. • The bonding continuum ranges from non-polar to ionic, however organic molecules are predominantly covalent molecules and lie in the polar to non-polar range. • Polar and non-polar regions affect solubility

5. Non-polar Polar Ionic 0 0.4 1.7 3.3 Organic compounds Intermolecular forces • The polarity of a bond is determined by the electronegativity difference. Electronegativity Difference (DE)

7. Intermolecular forces • The intermolecular forces are attractive and repulsive forces between molecules determined by factors such as: • The bond types within the molecules. • Polar vs. Non-polar • The size of the molecules. • The shape of the molecules.

8. Intermolecular forces • Johannes van der Waals (1837-1923) studied these forces and they are often referred to by his name. • We will focus on the three main types: • Dispersion (London) forces • Dipole-dipole forces • Hydrogen bonding

9. Intermolecular forces • Dispersion (London) forces • The constant vibration of electrons in covalent bonds generates temporary regions of charge distribution and polar regions which result in weak forces of attraction between all covalent molecules. • The overall strength of these forces is proportional to; • The number of electrons in the molecule • The size and shape of the molecule

10. Intermolecular forces • Dipole-Dipole Forces • Polar molecules orient themselves so that electrostatic attraction occurs between the different charged regions of the molecules. • These forces are generally stronger than the dispersion (London) forces. • Their strength depends upon the; • Nature (i.e. DE difference) of the polar bonds • Number and placement of the polar bonds • Size of the molecules

11. Intermolecular forces • Hydrogen bonding • A strong form of dipole-dipole attraction between a hydrogen atom and oxygen, nitrogen or fluorine in a polar covalent molecule. • The high electronegative difference results in a strong polar bond and distinct regions of charge distribution. • Hydrogen bonding is responsible for water’s unique characteristics and influences organic compounds’ solubility in water.

12. Assessing intermolecular forces • Can molecules form hydrogen bonds? • If so: • They have higher boiling and melting points than similar molecules that cannot form hydrogen bonds • They form hydrogen bonds with water and thereby have greater solubility in water

13. Assessing intermolecular forces • Are they polar? • Polar molecules tend to have higher boiling & melting points than similar non-polar ones. Hydrogen bonding capability increases the trend further. • A large non-polar region (hydrocarbon) in a molecule reduces the affect of the smaller polar regions and are less soluble than smaller hydrocarbon polar molecules.

14. Assessing intermolecular forces • How strong are the dispersion forces? • Large hydrocarbon chains have stronger dispersion forces. • The boiling and melting points tend to be proportional to the number of carbons in the hydrocarbon. • Large hydrocarbons have high boiling and melting points. • Small hydrocarbons tend to be gases at SATP.

15. Hydrocarbons(CnH2n+2) Physical Properties

16. Hydrocarbons(CnH2n+2) Additional Characteristics • As the number of carbons in the parent chain increase: • The state of matter at SATP moves from gas to liquid to solid • The melting and boiling points increase • The density increases • Popular fuel source (Methane, propane, octane, etc.) • Source for plastics

17. Alcohols (R-OH) Physical Properties

18. Alcohols Additional Characteristics • Alcohols are extremely flammable • Most alcohols are poisonous • Methanol can cause blindness or death. • Ethanol is consumed in moderate quantities. Excessive consumption may cause blindness or death. • Yeast ferment sugars to produce ethanol and carbon dioxide • Antifreeze, cosmetics, foods, medical preparations, solvents, antiseptics, etc. • Biological compounds – cholesterol, retinol, etc.

19. Ethers (R-O-R2) Physical Properties

20. Ethers Additional Characteristics • Ethers are extremely flammable • Have been used as anaesthetics • “ether” – ethoxyethane • More recent anaesthetic (1-methoxypropane) has fewer side effects.

21. Amines(R-NH2) Physical Properties

22. Amines Additional Characteristics • Widely found in nature. They are often toxic. Many medical applications. • Low molecular weight amines have a “fishy” smell while others are responsible for odours associated with decay. • Amines act as weak bases. Adding an acid produces a salt. So, add lemon to fish to remove fishy odour.

23. Aldehydes (R-COH) & Ketones Physical Properties

24. Aldehydes & Ketones Additional Characteristics • Aldehydes have a strong pungent odour while ketones smell sweet. As the size of the aldehyde increases the odour becomes more pleasant (i.e. cinnamon) • Odours in nature may be used to communicate between insects - pheromones • Since they are polar, they are used as polar solvents. The non-polar alkyl chain permits their use as non-polar solvents too. • Antiseptics, disinfectants (Formaldehyde), resins, dyes, preservatives (Aldehyde) • Hormones in biology – testosterone, progesterone, cortisone • Solvents, medication

25. Carboxylic acids (R-COOH) Physical Properties

26. Carboxylic acids Additional Characteristics • Carboxylic acids often have unpleasant odours • butanoic acid smells like stale sweat • Sour taste in many foods & plants – vinegar, spoiled wine, rhubarb, citrus fruits • By-product of anaerobic respiration in muscles – lactic acid • Industrial processes – dyes, tanning, rubber recycling, etc. • Food preservatives, Vitamin C, ASA • The OH does not behave like a base. The two O’s have high electronegativities and carry the H’s electron allowing the H ion to dissociate.

27. 0 = CH3CH2CCH3 0 = CH3CH2CH2CH 0 = CH3CH2CH2COH Boiling & Melting Points b.p. 165.5 oCm.p. -4.5 oC High Carboxylic acid b.p. 117.2 oCm.p. -89.5 oC Alcohol CH3CH2CH2CH2OH b.p. 79.6 oCm.p. -86.3 oC Ketone b.p. 75.7 oCm.p. -99 oC Aldehyde b.p. -0.5 oCm.p. -138.4 oC Alkane CH3CH2CH2CH3 Low

28. Esters (R-COO-R2) Physical Properties

29. Esters Additional Characteristics • Esters often have pleasant odours • Low molecular mass esters have very pleasant odours and are used in soaps, perfumes, cosmetics, air fresheners, etc. • Natural esters are responsible for the scents in flowers & fruits. (Pg 64 Table 2) • Food – lipids and dietary fats are esters (triglycerides)

30. Amides (R-CONHR2) Physical Properties

31. Amides Additional Characteristics • Amides such as acetaminophen are analgesics (pain killers) • Urea is a common amide found in urine and fertilizers

32. Practice Questions • Pg 10(bot) # 1,2 • Pg 42 # 4,5,6 • Pg 48 # 2 • Pg 52 # 5 • Pg 63 # 4 • Pg 78 # 2,10 • Pg 96 # 2,6,