AROMATIC SUBSTITUTION REACTIONS

NOMENCLATURE

Learn Nomeclature Either on Your Own or Use the Organic Nomeclature Software CH 3 CH 3 methylbenzene (toluene) Br 1-bromo-3-nitrobenzene NO 2 CH 3 1-chloro-3-methylbenzene Cl CH 3 1,4-dimethylbenzene

CH 3 SOME SPECIAL NAMES NH 2 O CH 3 OH toluene CH 3 CH 3 aniline CH 3 o -xylene anisole CH 3 CH 3 m -xylene CH 3 p -xylene phenol COOH benzoic acid

ortho

,

meta

and

para

Positions o 6 1 R m 5 4 p 2 ipso ortho meta 3 para CH 3 m -nitrotoluene 3-nitrotoluene NO 2 1-methyl-3-nitrobenzene Cl Cl p -dichlorobenzene 1,4-dichlorobenzene

Compounds containing aromatic rings are often used in dyes, such as these for sale in a market in Nepal

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REVIEW OF BENZENE PROPERTIES

Figure 22.11: The structure of benzene

BENZENE RESONANCE Review Sections 6.8 - 6.14

KEKULE STRUCTURES Resonance Energy = 36 Kcal / mole All bonds are equivalent The ring is symmetric.

Bond lengths are between a single and a double bond.

Very Stable Less reactive than other groupings of atoms.

H .

H .

.

H .

.

H .

H All 2p orbitals overlap equally.

H

BENZENE Isodensity surfaces - electron potential mapped in color.

(van der Waal

’

s) Highest electron density is red.

Note the symmetry.

Color adjusted to enhance the pi system.

BENZENE - DETERMINATION OF RESONANCE ENERGY cyclohexatriene

(hypothetical) + 3 H 2

cyclohexene +

H 2

benzene -28.6 kcal/mol

+ 3 H 2

RESONANCE ENERGY 36 kcal/mol -49.8 kcal/mol -85.8 kcal/mol (calculated) cyclohexane

REACTIVITY

R R R R The

“

Double Bonds

”

in a Benzene Ring Do Not React Like Others Alkene Benzene + H Cl R Cl + H Cl no reaction + Cl 2 R Cl H + Cl 2 no reaction + Br 2 R Br Cl + Br 2 no reaction + RCO 3 H R O Br + RCO 3 H no reaction

Benzene is a Weak Base and Poor Nucleophile Stronger base Weaker base H + Readily donates electrons to an electrophile.

alkene benzene H + Donation of electrons would interrupt ring resonance (36 kcal / mole).

A strong electrophile is required - and often a catalyst.

Benzene Reactivity Benzene requires a strong electrophile and a catalyst

…

..and then it undergoes substitution reactions, not addition.

+ Cl 2 FeCl 3 catalyst Cl + H Cl substitution compare: + Cl 2 no catalyst Cl Cl addition

Some Substitution Reactions of Benzene Cl AlCl 3 Halogenation + Cl 2 CH 3 Friedel-Crafts Alkylation Friedel-Crafts Acylation Nitration Sulfonation AlCl 3 + CH 3 Cl O + CH 3 C Cl AlCl 3 + H O + N O O O + H O S O OH H 2 SO 4 SO 3 O C CH 3 O O S O OH

Blood Alcohol Level

Alcohols and Water

• alcohols are “monosubstituted” water, ROH, hydrocarbon radical, R, substituted for one of the hydrogen atoms in water, HOH • alcohols form hydrogen bonds to other alcohol molecules, increasing boiling point, and to water, making them very soluble in water

Classes of Alcohols

Oxidation of Alcohols

primary alcohol  aldehyde  RCH 2 OH  RCHO  carboxylic acids RCOOH secondary alcohols  RCHOHR’  ketones RC=OR’ tertiary alcohols  No Reaction

Large Molecules Containing Alcohol Groups

More Large Molecules Containing

HO

Alcohol Groups

H 3 C OH H 3 C O estradiol (female hormone, an estrogen) H 3 C HO H 3 C estrone (female hormone, an estrogen) OH O testostrone (male hormone)

Ethanol is being tested in selected areas as a fuel for automobiles

Source:

AP/Wide World Photos

ALDEHYDES AND KETONES I

Aldehyde

O R

Ketone

C O H C R R'

STRUCTURE

R = H, alkyl, aryl R and R' = alkyl or aryl R and R' cannot be hydrogen!

Cinnamaldehyde produces the characteristic odor of cinnamon

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NOMENCLATURE

IUPAC Nomenclature of Ketones

• Choose the longest continuous carbon chain that contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon • Ketone ending is

-one

Do the

ketones

section of Organic Nomenclature program!

EXAMPLES

O CH 3 C CH 2 CH 2 CH 3

2-Pentanone

O CH 3 CH 2 C CH CH 2 CH 3 CH 2 CH 3

4-Ethyl-3-hexanone

O CH CH 3 CH 3

3-Isopropylcyclopentanone or 3-(1-Methylethyl)cyclopentanone

KETONES

Common, or Trivial, Names

• Name each group attached to the carbonyl group as an alkyl group • Combine into a name, according to the pattern: alkyl alkyl

’

ketone NOTE: This is not all one word!

Example of Common Names

O CH 3 C CH 2 CH 2 CH 3

Methyl propyl ketone

O CH 3 CH 2 C CH

Diethyl ketone

2 CH 3

O

SPECIAL CASES O C

C CH 3 CH 3

dimethyl ketone acetone A common laboratory solvent and cleaning agent diphenyl ketone benzophenone O C CH 3 KNOW THESE methyl phenyl ketone acetophenone

IUPAC Nomenclature of Aldehydes • Choose the longest continuous carbon chain that contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon (carbon #1!) • Aldehyde ending is -al Do the aldehydes program.

section of Organic Nomenclature

EXAMPLES H 3 C CH 2 CH 2 CH 2 C H pentanal O aldehyde group is always carbon 1 4 CH 3 Cl 3 CH CH 2 CH 3 1 C H O 2-chloro-3-methylbutanal

Common Names of the Aldehydes O O O C H H Formaldehyde 1 O CH 3 C H Acetaldehyde 2 C H 3 C CH 2 H Propionaldehyde 3 O H 3 C C CH 2 C Butyraldehyde H 4 H 3 C C CH 2 CH 2 C Valeraldehyde O 5 H H 3 C CH 2 CH 2 CH 2 CH 2 Caproaldehyde C 6 H RECOGNIZE THESE

O SPECIAL CASES C H H formaldehyde O O C H benzaldehyde C H CH 3 acetaldehyde KNOW THESE

Figure 22.13: Some common ketones and akdehydes

Figure 22.14: Some carboxylic acids

Computer-generated space-filling model of acetylsalicylic acid (aspirin)

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Photo Researchers, Inc.