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Chapter 25 – Organic Chemistry

Reading: sections 25.1 – 25.5 in 11th edition, sections 25.1-25.7 (in 10th edition)

As you read this material ask yourself the following questions:What is unique about carbon and carbon-based compounds? Why did life evolve around carbon?

Why does silicon not exhibit the great diversity if compounds that we find for carbon?

What are the main classifications of hydrocarbons?

How do the properties of structural isomers differ from one another?What is the difference between saturated and unsaturated hydrocarbons?

What is geometric isomerism in alkenes.

Chem 101 1

What kinds of reactions are common in alkenes and aromatics?

What are functional groups? Why are they important?

What are optical isomers or enantiomers? What sort of organicmolecules display this isomerism?

Organic chemistry, Chapter 25, sections 25.1- 25.5

The end to vitalism: living things have a vital force making it possible for them to form organic compounds

F. Wohler 1828

C

NH2

NH2 O

F. Wohler 1828

most odorants are organic compounds

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organic chemistry: study of compounds containing C in combination with one or more other elements

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Carbon is unique

tendency to form four covalent bonds

ability to form double and triple bonds

forms strong covalent bonds

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reactivity resides in– regions of high electron density, like C-O-H or C=O

carbon is unique, continued

tendency to catenate

solubility

water solubility is conferred by

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water solubility is conferred by

acidic groups

basic groups

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Hydrocarbons

four different types:

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largest possible no. of H atoms

Drawing hydrocarbon structures

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butane and isobutane

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Alkanes - general formula:

structures based on

Lewis structure and condensed formula do not tell 3D structure

Free rotation about single bonds give alkanesmany shapes

molecular formulas are the same

C C C C C C C

C

is the same as

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systematic names are required – IUPAC rules

Alkane nomenclature

1. Find the longest continuous chain of carbon atoms. This longest chain may not be written in a straight line.

2. Name that longest chain with the appropriate alkane name.

6 Precede each group name with a prefix indicating how many of them are

3. Find the substituents and name each of them with the appropriate group name.

4. Number the carbons in the chain such that the lowest number is given to the group nearest one end of the chain.

5. List the groups alphabetically in front of the longest chain name.

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6. Precede each group name with a prefix indicating how many of them are present in the molecule. In front of the prefix, list the numbers of each group in the molecule and separate the numbers with a hyphen.

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example:

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other substituents

halogens

CH3CH2CH2CHCH2CHCH2CH3| |

CH3 CH3

-F

-Cl

-Br

-I

-OH

C CH3H3C

CH3

CH3

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O

-NO2 write the structural formula for 3-chloro-2,4-dimethylpentane

Cycloalkanes - general formula:

carbon chains can form rings or cycles

well known and found in nature

CH2 CH2

CH2

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rings with fewer than 5 carbon atoms are strained

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cycloalkane nomenclature

1. add cyclo to parent name

2. start numbering at the substituent group with alphabetical priority

3. number around ring so that substituents have lowest possible numbers

CH3

Br

CH3

Br

1

CH3

Br12

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BrCH3

Br1

CH3

Br1

2

Reactions of alkanes

alkanes

combustion is important

methane and ethane

propane and butane – components in LPG (Liquefied petroleum gas)

also high mol. weight compounds: gasoline, oil, tar sands

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all alkanes have the same combustion reaction:

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Chapter 25 – Organic Chemistry – PART 2

Reading: sections 25.1-25.3 ( to p. 1062 in11th edition), sections 25.1-25.3 (complete, in 10th edition)

As you read this material ask yourself the following questions:

Explain geometric isomerism in alkenes.

What kinds of reactions are common in alkenes and aromatics?

What are functional groups? Why are they important?

What are optical isomers or enantiomers? What sort of organicmolecules display this isomerism?

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molecules display this isomerism?

Alkenes - general formula:

structures based on

at least two C atoms have

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unsaturated hydrocarbon -

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geometry of alkenes

geometry constrained

t i i

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geometric isomers

Nomenclature of alkenes

1. suffix is

2. parent = p

4. number the chain

3. position of double bond

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5. proceed as for alkanes

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examples

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alkene nomenclature cont’d…

geometric isomers ( if known) have to indicated in name

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16 6

cis and trans isomers can differ

4

6

1

5

2

3

4

6

3

5

2

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1

4

6

52

3

4

6

5

1

3 3

2

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Reactions of alkenes

addition reactions

general reaction:

Br2, Cl2

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Cl2

H2

addition rxns, cont’d

H2H2

H2O

H2OH2O

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addition rxns, cont’d

HBr

HBrHBrHBrHBr

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omit mechanism of addition reactions topic, pp. 1066 – 1068 (11th

edition), pp. 1079 – 1080 10th edition

Alkynes - general formula:

unsaturated

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addition reactions

2 H2

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Nomenclature of alkynes

1. suffix is

2. parent = p

4. number the chain

3. position of triple bond

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5. proceed as for alkanes

Aromatic hydrocarbons

contain a 6-membered ring with 3 double bonds

chemically unlike alkenes and alkynes

resonance structures

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aromatic nomenclature

(only need to know the compounds in the text)

parentparent

naphthalene

prefix

B

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CH3

Br

number

Br

Br

nomenclature, cont’d

Br

1, 2-dibromobenzene

Br

Br

Br 1, 3-dibromobenzene

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1, 4-dichlorobenzene

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Reactions of aromatics

substitution reactions

in general:

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HNO3

substitution rxns, cont’d

Br2

HNO3

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HNO3

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Summary of hydrocarbon reactions

CnH2n+2 O2 CO2 H2OCnH2n+2 O2 CO2 H2O

XY

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XY HY

Functional groups

group of atoms attached to hydrocarbon

two examples already reviewed:

most reactions involve regions of high electron density

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other common functional groups

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Alcohols

related to water and to alkanes

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properties of alcohols

weakly acidic

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H2O H3O+CH3O_

alcohol, preparation

methanol, called wood alcohol, prepared from CO and H2 in gas phase

ethanol – oldest known pure organic chemical, fermentation of sugar/ starch

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alcohol, preparation, cont’d

from alkenes, addition reaction

common alcohols:

ethylene glycol1 2 ethanediol

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phenol

1,2-ethanediol

glycerol1,2,3-propanetriol

Ethers (R-O-R’) CH2

OCH

3

CH2 CH

3

formed by the reaction between two alcohols

R1-O-H + H-O-R2

flammable – only slightly polar -

will oxidize in air to form

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used as anesthetics

or CF3CHCl-O-CF3 isoflurane

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Amines (R-NH2)

less polar than alcohols

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reacts with acid to form salts

amines, cont’d

Used in the manufacture of dyes

indigo

drugs are amines and amino group important functional group for amino acids, peptides and proteins

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Functional groups with a C=O group

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Aldehydes and Ketones

R

O

R 1 R

O

H

&

C atom has 3 electron domainsC atom has 3 electron domains

classified by the number of C atoms attached to carbonyl carbon atom

aldehyde

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ketone no H atoms attached

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aldehyde and ketone cont’d

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aldehydes and ketones, cont’d

many occur naturally

CHOH

ketones – solvents and perfumes

ld h d fl

HC

O

O

CH3

CH3aldehydes - flavours

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CH

O

O

H3CCH3

H3C

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Carboxylic acids

occur widely in nature

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H3C COOH

ethanoic acid or acetic acidquinic acid

carboxylic acids, cont’d…

behave as weak acids -

R COOH + H2O

can be neutralized by strong base

R COOH + NaOH

produced by oxidation of alcohols

CH3CH2CH2OH + [O]

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Esters

alkyl derivatives of carboxylic acids

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formed by condensation reaction between alcohols and carboxylic acids

examples

CH3CH2C

O

OH HO-CH2CH2CH3+

H+ catalyst

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ester reaction

saponificationp

CH3CH2C

O

+ H2OO[OH-]

CH3

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ester + water [OH-]

AmidesR

C N

O

H

resonance important:p

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key functional group in peptides and proteins

formation of amide linkage is the important step in protein synthesis

A1AC N

O

H

AA2

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amides, cont’d

neutral – does not accept H+ or form ammonium-like salts

prepared by reaction of carboxylic acid with ammonia or amine

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amides undergo hydrolysis

RC N

O

R1

R2+ H2O

H+

heat

Isomers

Isomers

structural isomers stereoisomers

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Optical isomers

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to have optical isomers need:

molecule that has optical isomers

molecules that are optical isomers

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Natural amino acids are chiral

CH2N

HHOOC

RL- alanine

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Chiral molecules:

H C Cl

H

Br C C H

H H

Br C C Cl

H H

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H C Cl

Br

Br C C H

Cl H

Br C C Cl

H H

A. B. C.