2 OF O RGANIC C OMPOUNDS C HOLESTEROL 2.1 STRUCTURE AND PHYSICAL - - PowerPoint PPT Presentation

2

PROPERTIES

OF

ORGANIC COMPOUNDS

CHOLESTEROL

Section 2.1 Structure and Physical Properties Dipole-Dipole Forces

2.1 STRUCTURE AND PHYSICAL PROPERTIES

Dipole-Dipole Forces

C Cl Cl Cl Cl

Te bond moments cancel and there is no net polarity

C H Cl H Cl

Te bond moments do not cancel and there is a net polarity Blue arrow: direction of net dipole moment Tetrachloromethane Dichloromethane

Section 2.1 Structure and Physical Properties Figure 2.1

Figure 2.1 Physical Properties of Isobutane and Acetone Te physical properties of these two molecules refmect their dipole

• moments. Isobutane, which has a dipole moment near zero, has a

low boiling point of -11.7 oC. Acetone, however, has a large dipole moment of 2.91 D and a boiling point of 56–57 oC. C CH3 CH3 CH3 H C O CH3 CH3

Isobutane, bp –11.7 oC Acetone, bp 56-57 oC

Section 2.1 Structure and Physical Properties London Forces

London Forces CH3CH2Br CH3CH2Cl Boiling point 38.4°C 12.3°C Molecular weight 109 amu 64.5 amu CH3H2CH2CH2CH3 CH3CH2CH2CHvCH2CH3 pentane hexane (bp 36 °C) (bp 69 °C)

Section 2.1 Structure and Physical Properties Figure 2.2 London Forces

Figure 2.2 London Forces (a) T e approach of one nonpolar molecule induces a transient dipole in its neighbor “end-to-end”. (b) Several nonpolar molecules interacting side-by-side by London interactions. δ+ δ+ δ+ δ+ δ+ δ+ δ- δ- δ- δ- δ- δ- δ+ δ- δ- δ+ induced dipoles δ- δ+ induced dipoles (a) (b) C CH3 CH3 CH3 CH3

2,2-dimethylpropane, bp 10 oC

CH3 CH2 CH2 CH2 CH3

pentane, bp 36 oC

Section 2.1 Structure and Physical Properties Figure 2.3 London Forces

Figure 2.3 London Forces Molecular models show how the difg erence in surface contact depends on molecular shapes. n-pentane large area of surface contact 2,2-dimethylpropane (neopentane) small area of surface contact

Section 2.1 Structure and Physical Properties Hydrogen Bonding Forces

Hydrogen-Bonding Forces H O H H O H

Hydrogen bond

H N H H H N H H

Hydrogen bond

C O H H H H H O C H H H Hydrogen bond

ethanol, bp 78.5 oC

CH3 O

dimethyl ether, bp -24 oC

CH3 OH CH2 CH3

Section 2.1 Structure and Physical Properties Figure 2.4 Hydrogen Bonding in Ethanol

Figure 2.4 Hydrogen Bonding in Ethanol

Section 2.1 Structure and Physical Properties Solubility

Solubility CH2 O H H O H

Hydrogen bond

CH3 H O H

Hydrogen bond

Figure 2.5 Water Soluble and Fat Soluble Vitamins Section 2.1 Structure and Physical Properties

Figure 2.5 Water-and Fat-Soluble Vitamins

N N N O CH3 CH3 OH HO OH OH O OH OH OH O

Vitamin C

N HO OH NH2

Vitamin B6 Riboflavin

Water-soluble vitamins O Fat-soluble vitamins

Vitamin A (retinol)

OH C (CH2)7 CH3 CH3 CH3 (CH2)3 C (CH2)3 H CH3 O HO

Vitamin E

HO

Vitamin D3

Brønsted-Lowry Acids Section 2.2-2.3 Chemical Reactions: Acid-Base Reactions

2.3 BRØNSTED-LOWRY ACIDS AND BASES

O H H this bond breaks + H Cl O H H H this bond forms + Cl N H H H + O H H H N H H H H O H H + N H O H H + O H H + H methylamine water, conjugate base methylammonium ion, conjugate acid hydronium ion CH3 H N H CH3 H H C O O CH3 H O H H + C O O CH3 O H H + H acetic acid water, a base acetate, conjugate base hydronium ion, conjugate acid

Lewis Acids Section 2.2-2.3 Chemical Reactions: Acid-Base Reactions

boron trifluoride B F F F Boron can accept an electron pair aluminum trichloride Al Cl Cl Cl Aluminum can accept an electron pair Br Br FeBr3 Br + Br FeBr3

Lewis acid Lewis base

O CH3 CH3 O CH3 CH3 H B F F F B F F F

2.3 LEWIS ACIDS AND BASES

2.4 OXIDATION-REDUCTION REACTIONS

H C H H H C H O

methanol

OH [O]

methanal (formaldehyde)

[O] H C OH O

methanoic acid (formic acid)

ethane C H H H C H H H C C H H H H ethene

+ H2

Pt C C H H ethyne C H H H C H H H

+ 2 H2

Pt C C H H H H + H2O H C C H H H OH H

ethene ethanol

CH2 O H C CH3 CH3 CH3

K2Cr2O7 H2SO4

C CH3 CH3 CH3 C OH O

Section 2.4 Redox Reactions Examples of Redox Reactions

Section 2.4 Redox Reactions, II Examples of Biochemical Redox Reactions

Biochemical Redox Reactions NAD+ + 2H+ + 2e- NADH + H+

• xidized form

reduced form

FAD + 2H+ + 2e- FADH2

• xidized form

reduced form

NAD+ + C CO2H CH2 OH H CO2H NADH + C CO2H CH2 O CO2H + H+

malic acid

• xaloacetic acid
• leic acid

stearic acid

C C CH2(CH2)6CO2H H H CH3(CH2)6CH2 enzyme C C CH2(CH2)6CO2H H H CH3(CH2)6CH2 H H FAD FADH2 NADP+ + NADPH + H+

• xidized form

reduced form

O2 R H + R OH + H2O

Cyt P450

+

Section 2.5 Classifjcation of Organic Reactions Examples of Addition, Elimination, and Substitution Reactions

2.5 CLASSIFICATION OF ORGANIC REACTIONS

C C H H CH3 H H C C H H CH3 OH H

propene 2-propanol

H OH +

elimination

H2SO4 C C H H H H H C C H H H Br H

ethene bromoethane

H Br +

addition

Y

substitution

R X + X R Y + OH

substitution

CH3 Br + Br + CH3 OH

bromomethane methanol

Section 2.5 Classifjcation of Organic Reactions, II Examples of Hydrolysis, Condensation, and Rearrangement Reactions

CH3 C O O + HO H CH3 C OH O + CH3 H O CH3

methyl acetate hydrolysis acetic acid methanol this bond breaks this bond breaks these bonds form

CH3 C O O + HO H CH3 C OH O + CH3 H O CH3

methyl acetate condensation acetic acid methanol this bond forms these bonds break this bond forms

CH CH2 C CH3 H Br CH CH3 CH Br CH2

2.5 CLASSIFICATION OF ORGANIC REACTIONS

rearrangement

Section 2.6 Chemical Equilibrium and Equilibrium Constants Equations for Equilibrium Constants

2.6 CHEMICAL EQUILIBRIUM AND EQUILIBRIUM CONSTANTS

Kequilibrium = + HBr CH3CH2Br [CH3CH2Br] [CH2=CH2][HBr] = 108 Keq ethene CH2 CH2 Kequilibrium = + [CH3CO2CH2CH3] = 4.0 Keq ethanoic acid [H2O] [CH3CO2H] [CH3CH2OH] CH3 C O OH CH3CH2OH ethyl ethanoate CH3 C O OCH2CH3 ethanol + H2O m A + n B forward reaction reverse reaction p X + q Y Kequilibrium = [X]p [Y] [A]m [B]n

q

Section 2.6 Chemical Equilibrium and Equilibrium Constants Le Châtelier’s Principle

Le Châtelier’s Principle C H H H C O O C H H H H OCH2CH3 C O + CH3CH2OH H2O Adding ethanol pushes the reaction to the right Removing water pulls the reaction to the right +

Section 2.7 Equilibria in Acid-Base-Reactions Table 2.1 Acidity of Common Acids

HA Keq + H2O A- + H3O+ Kequilibrium = [H3O+][A-] [HA][H2O]

2.7 EQUILIBRIA IN ACID-BASE REACTIONS

[H3O+][A-] [HA] Ka = Keq[H2O] = Table 2.1 Ka and pKa Values of Common Acids Acid Ka pKa HBr 109

• 9

HCl 107

• 7

H2SO4 105

• 5

HNO3 101

• 1

HF 6 x 10-4 3.2 CH3CO2H 2 x 10-5 4.7 (CF3)3COH 2 x 10-5 4.7 CH3CH2SH 3 x 10-11 10.6 CF3CH2OH 4 x 10-13 12.4 CH3OH 3 x 10-16 15.5 (CH3)3COH 1 x 10-18 18 CCl3H 10-25 25 HC≡CH 10-25 25 NH3 10-36 36 CH2=CH2 10-44 44 CH4 10-49 49

Section 2.7 Equilibria in Acid-Base-Reactions, II Weak and Strong Acids, Conjugate Acids and Bases

[HA][OH-] [A-] Kb = Keq[H2O] = A- + H2O HA + OH-

CH3CO2H Kb + OH– + H2O CH3CO2– weak base strong base

CH3CO2H + H2O + H3O CH3CO2

stronger base than H2O weaker acid than H3O+ conjugate acid-base pair weaker base than CH3CO2- conjugate acid-base pair stronger acid than CH3CO2H

2.7 EQUILIBRIA IN ACID-BASE REACTIONS, II

Section 2.7 Equilibria in Acid-Base-Reactions, III Table 2.2 Basicity of Common Bases

Table 2.2 Kb and pKb Values of Common Bases Acid Kb pKb

NH2

4 x 10-10 9.4 CH3CO2

–

5 x 10-10 9.3 C≡N– 1.6 x 10-5 4.8 NH3 1.7 x 10-5 4.8 CH3NH2 4.3 x 10-4 3.4

CH3O–

3 x 10-16

• 1.5

CH3NH2 Kb + H2O + OH- CH3NH3+ weak base strong base

CH3NH2 + OH + H2O CH3NH3

stronger acid than H2O weaker base than OH- conjugate acid-base pair weaker acid than CH3NH3+ conjugate acid-base pair stronger base than CH3NH2

2.7 EQUILIBRIA IN ACID-BASE REACTIONS, III

Section 2.8 Efgect of Structure on Acidity Efgect of Structure on Acidity, Resonance, and Inductive Efgects

O S O O O

sulfuric acid, a strong acid

O S O OH O

methane sulfonic acid, a strong acid

CH3 H H N H H H ammonia pKb 4.74 (weak base) ethylamine pKb 3.25 (weak base) N H H CH2CH3 CH3 C O O CH3 C O O C C O O H Cl H H

pKa = 2.9

C C O O H H H H

pKa = 4.7

CH3OH + H2O CH3O- + H3O+ Ka = 10-16 CH3CO2H + H2O CH3CO2- H3O+ Ka = 1.8 10-5 +

C C O O H Cl H H

2.8 EFFECT OF STRUCTURE ON ACIDITY

Section 2.9 Introduction to Organic Reaction Mechanisms Reactions Tat Proceed Trough an Intermediate

2.9 INTRODUCTION TO REACTION MECHANISMS

A P reactant product A M reactant intermediate Step 1 P M product intermediate Step 2

X general reaction for homolytic bond cleavage Y X Y + X general reaction for heterolytic bond cleavage Y X Y + R (a carbanion) Y R Y + R (a carbocation) Y R Y + Types of Bond Cleavage and Formation

Section 2.9 Introduction to Organic Reaction Mechanisms Homolytic and Heterolytic Bond Cleavage

R (a carbanion) Li R Li +

δ δ

R (a carbocation) Br R Br +

δ δ

E Nu: E Nu

nucleophile electrophile

Section 2.9 Introduction to Organic Reaction Mechanisms, III Free Radical Substitution Reactions

Free Radical Substitution Reactions CH3 H + Cl Cl CH3 Cl + Cl H Step 1 Cl Cl Cl + Cl Cl CH3 H + CH3 + Cl H Step 3 Cl Cl Cl CH3 Cl + CH3 + Step 2

Section 2.9 Introduction to Organic Reaction Mechanisms, IV Nucleophilic Substitution Reactions

Nucleophilic Substitution Reactions R L Nu: R Nu + L

nucleophile nucleophilic substitution leaving group

H C I H H Br H C Br H H + I

Section 2.10 Reaction Rates, I Factors Tat Efgect Reaction Rates

2.10 REACTION RATES

+ H Br C C H H H H Br H

These two atoms add to adjacent carbon atoms

C C H H H H

These bonds are broken New C-H and C-Br bonds form

Factors that Affect Reaction Rates 1. Te nature of the reactants. 2. Te concentration of the reactants. 3. Temperature. 4. Te presence of substances called catalysts.

Section 2.10 Reaction Rates, II Reaction Rate Teory, Transition States

bond being formed bond being broken δ+ δ- δ- C H H H I Br

δ- δ- δ+

bond being broken bond being formed Reaction Rate Theory, Transition States

Section 2.10 Reaction Rates, III Reaction Coordinate Diagram for a Substitution Reaction

Reaction Coordinate Diagrams Figure 2.6 Reaction Coordinate Diagram for a Substitution Reaction Te reaction of hydroxide ion with chloromethane occurs in a single step. Te activation energy, Ea, refmects the stability of the transition state, which depends upon the structure of the sub- strate, the nucleophile, and the leaving group.

OH– + CH3Cl

Progress of reaction ∆H rxn < 0 E Energy

a

CH3OH + Cl–

C H Cl H H HO C H H H HOδ Cl δ C H O H H H + Cl

C C H H H H H C C H H H H H C C H H H H H C C H H H H H (electrophile) (carbocation) Step 1 Step 2 Br (nucleophile) Br slow fast

Section 2.10 Reaction Rates, IV Reaction Coordinate Diagram for an Addition Reaction

Figure 2.7 Energy Diagram for the Addition of HBr to an Alkene

Te fjrst, rate-determining step in the addition of HBr to ethene is the attack of the electrons of the double bond

• n a proton to give a carbo-
• cation. Te second step occurs

at a faster rate because the ac- tivation energy of the second step is lower than for the fjrst step.

Energy

Reactants Products Transition state 1 Carbocation Transition state 2

Progress of reaction

Ea1 Ea2 Reaction Coordinate Diagrams, II

Figure 2.8 Energy Diagram for a Catalyzed and an Uncatalyzed Reaction

Te activation energy for a catalyzed reaction is smaller than the activation energy for reaction in the absence of a catalyst. Te catalyzed reaction may require a difgerent number of steps than the uncatalyzed reaction. ∆Ho

rxn

Ea-cat Ea-uncat Products Reactants Energy Progress of reaction Transition state stabilization The Function of Catalysts A + C A C Step 1 B + A C Step 2 A B + C

Section 2.10 Reaction Rates, V Te Function of Catalysts