Functional Groups Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 1.

Functional Groups

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Functional groups are• a characteristic feature of organic molecules

that behave in a predictable, similar way. • composed of an atom or group of atoms. • groups that replace a hydrogen atom in the

corresponding alkane.• a way to classify families of organic

compounds.

Functional Groups

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Alkenes and Alkynes

Alkenes contain a double bond between adjacent carbon atoms.(Double bond: 4 electrons)

Alkynes contain a triple bond.(Triple bond: 6 electrons)

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OH- vs -OH

• OH- : hydroxide anion found in bases (e.g NaOH)

• -OH: hydroxyl group colvalently bound to carbon atom in an organic compound

(e.g. ethanol CH3-CH2OH)

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2. Ethers

In an ether, an oxygen atom is bonded to two carbon atoms.

–C–O–C– .

has a common name that gives the alkyl names of the attached groups followed by ether.

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Diethyl ether

3. Aldehydes

An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom.

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acetaldehydeformaldehyde

4. Ketones

In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms.

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Acetone

5. Carboxylic Acids and Esters

Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group.

O ║

— C—OH

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Acetic acid

5. Esters

An ester contains the carboxyl group between carbon atoms.

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Methyl acetate

Organic compounds with Carbon-Nitrogen bonds

1. AminesIn amines, the functional group is a nitrogen atom.

H H

C —N – H or C —N —C

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Methyl amineDimethyl amine

Naming simple amines

• Simple 1º amines are named as “alkylamine”– Examples:

• methylamine CH3NH2

• ethylamine CH3CH2NH2

• butylamine CH3CH2CH2CH2NH2

• Symmetrical 2º or 3º amines are named as

“dialkylamine” or “trialkyamine”– Examples:

• diethylamine (CH3CH2)2NH;

• trimethylamine (CH3)3N

NH3 NH2R NH

R

R

N

R

R

RAmmonia A primary amine A secondary amine A tertuary amine

Examples:

R

R

R

NH2

R

R

R

OH

A primary amine A tertuary alkcohol

NH2

pentan-2-amine

NH2

cyclohexanamine

NH

N-methylcyclohexanamine

Amines are much more polar, than hydrocarbons, especially in acidic conditions

Heterocyclic amines

• Some amines have a nitrogen as part of a ring. These generally have common (non-systematic) names:

NH2

N N

N

N

H

N

N

H

N

H

N

N

HN

aniline pyridine pyrimidine pyrrole

quinoline indole imidazole benzimidazole

Properties of amines

• Amines are moderately polar and are capable of hydrogen bonding.

• Low MW amines (up to about C5) are soluble in water; higher MW amines will dissolve in acidic solution (as their conjugate acid).

• Many amines have foul odors.

• Amines are weak bases.

Example of biologically active amines

H2NCH2CH2CH2CH2NH2 putrescine H2NCH2CH2CH2CH2CH2NH2 cadaverine

H2NCH2CH2CH2CH2NCH2CH2CH2CH2NH2 s permidineH

H2N(CH2)N(CH2)4N(CH2)3NH2 s permineH H

NHCH3

OHH

HO

HO

epinephrine(adrenaline)

NH2

OHH

HO

HO

norepinephrine(noradrenaline)

NH2HO

HO

dopamine

More biologically active amines…

NH2

CH3H

amphetamine(benzadrine)

N

CH2CH2NH2

HO

H

NHCH3

CH3H

methamphetamine (speed)

serotonin

mescaline

NH2CH3O

CH3O

OCH3

N

CO2H

nicotinic acid(niacin)

NN

CH2CH2NH2

H

histamine

More biologically active amines…

H2N C OCH2CH3

O

benzocaine(a topical anesthetic)

Cl

N

N

H

O

O

diazepam (Valium)

N

N

O

NN

CH3

CH2CH2CH3

H

SOO

N

NCH3

CH3CH2O

Sildenafil (Viagra)

Learning Check

Classify each of the following as: alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine or amide.

1) CH3─CH2─CH2─OH

2) CH3─O─CH2─CH3

3) CH3─CH2─NH2

O O ║ ║

4) CH3─C─OH 5) CH3─C─O─CH3

alcohol

ether

amine

carboxylic acid ester

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Organic compounds with

Carbon-Oxygen bonds1. Alcohols

An alcohol contains the hydroxyl (-OH) functional group.(instead of an H in that place)

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Ethanol

Alcohols

An alcohol contains a hydroxyl group (—OH) attached to a carbon chain.

A phenol contains a hydroxyl group (—OH) attached to a benzene ring.

water alcohol phenol

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Naming Alcohols

The names of alcohols• in IUPAC replace the -e with -ol.• with common names use the name of the alkyl group followed by alcohol.

Formula IUPAC Common Name

CH4 methane

CH3─OH methanol methyl alcohol

CH3─CH3 ethane

CH3─CH2─OH ethanol ethyl alcohol

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Classification of alcohols is• determined by the number of alkyl groups attached to

the carbon bonded to the hydroxyl.• primary (1°), secondary (2°), or tertiary(3).

Primary (1º) Secondary (2º) Tertiary (3º)1 group 2 groups 3 groups H CH3 CH3

| | | CH3—C—OH CH3—C—OH CH3—C—OH

| | | H H CH3

Classification of Alcohols

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Properties of Alcohols and Ethers

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Boiling Points of Alcohols

Alcohols• contain polar OH

groups. • form hydrogen bonds

with other alcohol molecules.

• have higher boiling points than alkanes and ethers of similar mass.

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Boiling Points of Ethers

Ethers• do not have a polar

group.• have an O atom,

but there is no H attached.

• cannot form hydrogen bonds between ether molecules.

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Solubility of Alcohols and Ethers in Water

Alcohols and ethers • are more soluble in water than alkanes because the

oxygen atom can hydrogen bond with water.

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Comparing Solubility and Boiling Points

Molar Boiling Soluble

Compound Mass Point (°C) in Water?

Alkane CH3─CH2─CH3 44 -42 No

Ether CH3─O─CH3 46 -23 Yes

Alcohol CH3─CH2─OH 46 78 Yes

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