II. Properties of Water. II. Organic Chemistry. A. Hydrocar bons--nonpolar

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1 II. Properties of Water 1. Ice and Liquid water structure 2. Cohesion / Surface Tension 3. High Heat Capacity 4. Solvent Properties 5. Dissociation: Acids & Bases / ph II. Organic Chemistry A. Hydrocar bons--nonpolar 1. alkanes-only single bonds 2. alkenes- C=C double bonds 3. aromatic-cyclic based on benzene B. Functional Groups: alcohol, aldehyde, ketone, carboxyl, amine, organophosphate, sulfhydral 1. polar bonds between C and more electronegative atoms (O and N) 2. Combine two functional groups ester = alcohol + acid 3. amide = amine + acid C. Isomers 1. Same chemical formula but differ in arrangement of atoms in space 2. Enantiomers (Optical Isomers): C can be bonded to 4 different groups in 2 ways producing molecules that are mirror images of one another that cannot be superimposed

2 Water As A Solvent For Life 75% of the Earth s surface is covered with water Water is essential for life on Earth All living organisms require water more than any other substance

3 Fig. 3.2: Water: Structure and Properties Hydrogen bond acceptors Hydrogen bond donors Water s molecular structure and capacity to donate and accept hydrogen bonds give it unusual critical properties that are significant for life

4 Fig. 3.6: Five Critical Properties of Water 1. Ice and liquid water structure Hydrogen bond Ice Hydrogen bonds are stable Liquid water Hydrogen bonds break and re-form Temperature 0 C Temperature > 0 C < 100 C Ice is less dense than liquid water Water is liquid at a relatively high temperature > 0 C (Methane (CH 4 ) is similar in size but liquid only below -161 C)

5 Fig. 3.3/3.4: Five Critical Properties of Water 2. Cohesion Hydrogen bonds hold water molecules together in liquid High Surface tension Water transport in plants Fig. 3.4

6 Five Critical Properties of Water 3. Moderation of temperature Heat energy can be absorbed by breaking hydrogen bonds Water has a high specific heat capacity specific heat capacity = amount of energy required to raise temperature of 1 g of water by 1 C (1 calorie, 1 cal) Large bodies of water stabilize the air temperature.

7 Fig. 2.15/3.7: Five Critical Properties of Water 4.Water as a solvent A sphere of water molecules, called a hydration shell, surrounds each solute ion Fig Fig. 3.7

8 Fig. 3.8: Five Critical Properties of Water 4. Water as a solvent (Cont d) Fig. 3.8 (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment (c) Ionic and polar regions on the protein s surface attract water molecules. Review solute concentration in aqueous solutions (Molarity) (page of text)

9 Five Critical Properties of Water 4. Water as a solvent (Cont d)

10 Page 53 H 3 O + (hydronium ion) OH - (hydroxide ion) This reaction is frequently abbreviated as: H 2 O H + + OH - The K W is the ion product of water, K w = [H + ][OH - ] = 1.0 x M 2 at 25 C Thus, in pure water, [H + ] = [OH - ] = 1.0 x 10-7 M

11 Fig. 3.9: ph SCALE x 10-7 M is a very small number and can change by orders of magnitude (powers of 10x) ph ph = -log[h + ] = 7 in pure water at 25 C = neutral ph Physiological ph (ph )

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13 CH 3 -C O OH CH 3 -C O O - + H + NH 3 + H + NH 4 +

14 CH 3 COOH CH 3 COO - + H + NH 4 + NH 3 + H + K a pk a 1.8 x 10-5 M x M 9.2 HA A - + H + Acid ionization constant, K a = [H + ][A - ] [HA] pk a = -log K a pk a is a measure of propensity to dissociate: if ph < pk a the HA form predominates if ph > pk a the A - form predominates

15 [HA] >> [A - ] [HA] = [A-] [A - ] >> [HA] Buffers keep ph relatively constant in the range around pka value by accepting or donating H + from solution CH 3 -C O OH Response to decrease [H + ] Response to increase [H + ] CH 3 -C O O -

16 Organic Chemistry The chemistry of molecules containing carbon bonded to other elements, principally: H, O, N, P, S

17 Hydrocarbons are Nonpolar (electrons are equally distributed) and do not mix freely with water they are Hydrophobic

18 Fig. 4-3 Fig. 4.3: The Shapes of Three Simple Organic Molecules Name and Comment Molecular Formula Structural Formula Ball-and- Stick Model Space-Filling Model (a) Methane CH 4 (b) Ethane C 2 H 6 (c) Ethene (ethylene) C 2 H 4

19 Hydrocarbons -- organic compounds containing only carbon and hydrogen. These are the most reduced organic compounds and react vigorously (i.e. burn) with oxygen. CH 4 + 2O 2 CO 2 + 2H 2 O + Heat Heat 2 2 Methane (natural gas) Oxygen Carbon Dioxide Water

20 Fig. 4.5: Various Hydrocarbons (a) Length (c) Double bond position Ethane Propane 1-Butene 2-Butene (b) Branching (d) Presence of rings Butane 2-Methylpropane (isobutane) Cyclohexane H H H H H H H H H-C-C-C-C-C-C-C-C-H H H H H H H H H Octane C 8 H 18 : A major component of gasoline. Benzene

21 Aromatic Hydrocarbons -- are a special class of hydrocarbons in which atoms are arranged in a ring structure and are connected by σ-bonds and a system of π-bonds around the ring. The simplest example is benzene, C 6 H 6, and as shown below all atoms lie on a plane with bond angles of

22 Fig. 4.4: Carbon also forms bonds with a variety of other Elements Hydrogen (valence = 1) Oxygen (valence = 2) Nitrogen (valence = 3) Carbon (valence = 4) H O N C Carbon dioxide (CO 2 ) O C O Urea CO(NH 2 ) Urea

23 Functional Groups Here R represents the rest of the molecule Carbonyls O O O O R OH R C R C R C R NH 2 R SH R O P OH H R OH OH Alcohol Aldehyde Ketone Carboxylic Acid Amine Sulfhydral Organic Phosphate Ethanol Acetone Acetic Acid

24 Fig. 5-2a Fig. 5.2a: The Synthesis of Polymers (a) Dehydration reaction: synthesizing a polymer Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond Longer polymer

25 Linking Functional Groups Polymers Organic molecules with certain functional groups can be joined by a covalent bond formed when a molecule of water is removed; this allows the creation of new types of organic molecules. Ester Amide R C O OH + HO R R C O O + H 2 O R C R C O-R OH + H N-R H H O + H 2 O N-R O R-OH + HO-P-OH O - O R-O-P-OH + H 2 O O -

26 Fig. 4.6: Ester bonds link fatty acid carboxyl groups to OH- groups of Glycerol Nucleus Fat droplets 10 µm (a) Part of a human adipose cell (b) A fat molecule a.k.a. Triglyceride

27 Isomers: Molecules that have the same chemical formula, i.e. the same number of each of the different kinds of atoms.

28 Fig. 4.7: There are different classes of Isomers cis isomer: The two X s are on the same side. trans isomer: The two X s are on opposite sides. L isomer D isomer

29 Fig. 4-8 Fig. 4.8: Pharmacological Importance of Enantiomers Drug Condition Effective Enantiomer Ineffective Enantiomer Ibuprofen Pain; inflammation S-Ibuprofen R-Ibuprofen Albuterol Asthma R-Albuterol S-Albuterol

30 Thalidomide was first used as a sedative and anti-nausea medication, but was found to cause serious birth defects when pregnant women take it during their first trimester.