New chm 152_unit_12_power_points-su13

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Chapter 15

Organic Compounds and the

Atomic Properties of Carbon

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ORGANIC CHEMISTRY II

• ALCOHOLSCLASSIFICATION

NOMENCLATURE

PREPARATION

REACTIONS

Chapter 15.3-15.4 Silberberg

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Organic Compounds and the Atomic Properties of Carbon

15.3 Some Important Classes of Organic Reactions

15.4 Properties and Reactivities of Common Functional Groups

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Goals & Objectives

• See the Learning Objectives on page 618.

• Understand these Concepts:• 15.7-11.

• Master these Skills:• 15.15.4-6.

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Haloalkanes

Haloalkanes or alkyl halides contain a halogen atom bonded to carbon.

Haloalkanes are named by identifying the halogen with a prefix on the hydrocarbon name. The C bearing the halogen must be numbered.

C X

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Reactions of Haloalkanes

Haloalkanes undergo substitution and elimination reactions.

CH3 CH2 CH2 CH2 Br + OH- CH3 CH2 CH2 CH2 OH + Br-

1-bromobutane 1-butanol

CH3 C

CH3

Cl

CH3 CH3 CH2 O-K++ CH3 C

CH3

CH2 + KCl + CH3 CH2 OH

2-chloro-2-methylpropane

potassium ethoxide 2-methylpropene ethanol

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Alkenes

Alkenes contain the C=C double bond:

Alkenes typically undergo addition reactions. The electron-rich double bond is readily attracted to the partially positive H atoms of H3O+ ions and hydrohalic acids.

C C

CH3

C CH2CH3 + H3O+

CH3

C CH3CH3

OH

OH

+ H+

2-methylpropene 2-methyl-2-propanol

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Aromatic Hydrocarbons

Benzene is an aromatic hydrocarbon and is a resonance hybrid. Its p bond electrons are delocalized.

Aromatic compounds are unusually stable and although they contain double bonds they undergo substitution rather than addition reactions.

+ Br2

FeBr3

Br

+ HBr

benzene bromobenzene

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Reactions of Hydrocarbons

1. Complete oxidation (combustion) produces CO2 + H2O

2. Reactions with halogens a. alkanes react by substitution b. alkenes react by addition c. benzene reacts by substitution

3. Reactions with hydrogen halides alkenes react by addition

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Reactions of Hydrocarbons

4. Reactions of aromatic compounds with HNO3/H2SO4

5. Reaction of alkenes with hydrogen hydrogenation

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Types of Organic Reactions

An addition reaction occurs when an unsaturated reactant becomes a saturated product:

R CH CH R + X Y R CH CH R

X Y

The C=C, CΞC, and C=O bonds commonly undergo addition reactions.In each case, it is the π bond that breaks, leaving the σ bond intact.

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CH2 CH2 + H Cl H CH2 CH2 Cl

Reactants (bonds broken)

1 C=C = 614 kJ 4 C–H = 1652 kJ1 H–Cl = 427 kJ

Total = 2693 kJ

Products (bonds formed)

1 C–C = -347 kJ 5 C–H = -2065 kJ1 C–Cl = -339 kJ

Total = -2751kJ

DH°rxn = SDH°bonds broken + SDH°bonds formed = 2693 kJ + (-2751 kJ) = -58 kJ

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Figure 15.14 A color test for C=C bonds.

This compound has no C=C bond, so the Br2 does not react.

C C + Br2 C C

Br

Br

Br2 (in pipet) reacts with a compound that has a C=C bond, and the orange-brown color of Br2 disappears.

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An elimination reaction occurs when a saturated reactant becomes an unsaturated product.This reaction is the reverse of addition.

The groups typically eliminated are H and a halogen atom or H and an –OH group.

R CH CH R + X YR CH CH R

X Y

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The driving force for an elimination reaction is the formation of a small, stable molecule such as HCl (g) or H2O.

R CH CH R + H OHR CH CH R

OH HH2SO4


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A substitution reaction occurs when an atom or group from an added reagent substitutes for one attached to a carbon in the organic reagent.

The C atom at which substitution may be saturated or unsaturated, and X and Y can be many different atoms.

R C X + Y R C Y + X

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CH3 C

O

Cl + HO CH2 CH2 CH

CH3

CH3 CH3 C

O

O CH2 CH2 CH

CH3

CH3

+ H Cl

The main flavor ingredient in banana oil is formed through a substitution reaction:


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Sample Problem 15.3 Recognizing the Type of Organic Reaction

PLAN: We determine the type of reaction by looking for any change in the number of atoms bonded to C.

• An addition reaction results in more atoms bonded to C.• An elimination reaction results in fewer atoms bonded to

C.• If there are the same number of atoms bonded to C, the

reaction is a substitution.

PROBLEM: State whether each reaction is an addition, elimination, or substitution:

CH3 CH2 CH2 Br CH3 CH CH2 + HBr(a)

(c) CH3 C

O

Br + CH3CH2OH CH3 C

O

OCH2CH3 + HBr

(b) + H2

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Sample Problem 15.3

SOLUTION:

CH3 CH2 CH2 Br CH3 CH CH2 + HBr(a)

This is an elimination reaction; two bonds in the reactant, C–H and C –Br, are absent in the product.

(b) + H2

This is an addition reaction; two more C–H bonds have formed in the product.

(c) CH3 C

O

Br + CH3CH2OH CH3 C

O

OCH2CH3 + HBr

This is a substitution reaction; the reactant C–Br bond has been replaced by a C–O bond in the product.

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Functional Groups

Organic compounds are classified according to their functional groups, a group of atoms bonded in a particular way.

The functional groups in a compound determine both its physical properties and its chemical reactivity.

Functional groups affect the polarity of a compound, and therefore determine the intermolecular forces it exhibits.

Functional groups define the regions of high and low electron density in a compound, thus determining its reactivity.

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Alcohols

The alcohol functional group consists of a carbon bonded to an –OH group.

C O H

Alcohols are named by replacing the –e at the end of the parent hydrocarbon name with the suffix –ol.

Alcohols have high melting and boiling points since they can form hydrogen bonds between their molecules.

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Reactions of Alcohols

Alcohols undergo elimination and substitution reactions.OH

H+

cyclohexanol cyclohexene

+ H2O dehydration (elimination)

CH3 CH2 CH

OH

CH3

K2Cr2O7

H2SO4

CH3 CH2 C

O

CH3

OH O

2-butanol 2-butanone

oxidation (elimination)

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Figure 15.15 Some molecules with the alcohol functional group.

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Alcohols, ROH

• Classification– locate the C to which the OH is attached– count the number of C atoms bonded

directly to that carbon atom.

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Classification of Alcohols

• If its bonded to one or none, it is a primary alcohol (1O)– CH3OH, CH3CH2OH, etc.

– RCH2OH

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If bonded to two, it is a secondary alcohol (2O). (CH3)2CHOH RCHOH R’

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If bonded to three, it is a tertiary alcohol (3O). (CH3)3COH R’ RCOH R’’

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Nomenclature of Alcohols

Common IUPAC CH3OH

CH3CH2OH

CH3CH2CH2OH

(CH3)2CHOH

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Preparation of Alcohols

• Laboratory Preparation• RX + NaOH -----> ROH + NaX• Prepare the following alcohols:

– 2-propanol– 2-methyl-2-propanol– 2,4-dimethyl-3-pentanol

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• 1. with sodium metal– ROH + Na ----> RONa + H2

– alcohol sodium alkoxide

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• 2. with HX - halogens– ROH + HX ----> RX + H2O

– CH3OH + HCl ----> CH3Cl + H2O

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• 3. with oxidizing agents, [O]– 1O alcohols react in two steps

• RCH2OH + [O] ----> RCHO (aldehyde)

• RCH2OH + xs[O] ----> RCOOH (CA)

– 2O alcohols react in one step• RCH(OH)R’ + [O] ----> RCOR’ (ketone)

– 3O alcohols do not react• R3COH + [O] ----> No Reaction

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Examples

• Give the expected organic product for each of the following reactions:– 2-butanol + [O] ---->– 1-pentanol + xs[O] ---->– 2-methyl-2-pentanol + HCl ---->– 3-methyl-2-butanol + Na ---->– 2-methyl-2-propanol + [O] ---->– 2-butene + Cl2 ---->

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Oxidation of alcohols with chromic acid or PCC - pyridinium chlorochromate.

Chromic acid is of ten used to convert secondary alcohols to ketones.

OH

K2Cr2O7

H2O H2SO4

O

HO

KMnO4O

OH

KMnO4 is an example of an oxidizer [O]

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