Introduction to Organic Chemistry: Alkanes Functional Groups
Dec 28, 2015
Elements in Organic Compounds
In organic molecules,carbon atoms bond • with four bonds.• mostly with H and
other C atoms.• sometimes to O, N,
S, • sometimes to
halogens F, Cl, and Br.
Functional groups are• a characteristic feature of organic molecules that
behave in a predictable 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
Alkenes and Alkynes
Alkenes contain a double bond between adjacent carbon atoms.
Alkynes contain a triple bond.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Alcohols and Ethers
An alcohol contains the hydroxyl (-OH) functional group.
In an ether, an oxygen atom is bonded to two carbon atoms.
–C–O–C– .
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Aldehydes and Ketones
An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom.
In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Carboxylic Acids and Esters
Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group.
O ║
— C—OH
An ester contains the carboxyl group between carbon atoms.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Amines and Amides
In amines, the functional group is a nitrogen atom.
|
—N —
In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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
Solution
1) CH3─CH2─CH2─OHalcohol
2) CH3─O─CH2─CH3 ether
3) CH3─CH2─NH2 amine
O O ║ ║ 4) CH3─C─OH 5) CH3─C─O─CH3 carboxylic acid ester
Some functional groups in consumer products
BENGAYCamphor – a ketoneMenthol – an alcoholMethyl salicylate – an ester and a phenol
Neopsporin Miconazole – many functional groups (ether,
chloro)Dimethyl ether propellent
Halls coughMenthol- an alcohol
Some functional groups in spices
Nutmeg Myristicin – a polyether, an aklene, benzene ring Elemicin Safrole
Anise Anethole – an ether, an alkene, benzene ring
Caraway seeds d-Carvone – a ketone
Spearmint l-Carvone – a ketone
Saturated hydrocarbons• have the maximum number of hydrogen atoms
attached to each carbon atom.• are alkanes and cycloalkanes with single C-C
bonds.
CH3—CH2—CH3
Saturated Hydrocarbons
Unsaturated hydrocarbons• have fewer hydrogen
atoms attached to the carbon chain than alkanes.
• are alkenes with double bonds.
• are alkynes with triple bonds.
Unsaturated Hydrocarbons
Bond Angles in Alkenes and Alkynes
According to VSEPR theory: • the three groups bonded to
carbon atoms in a double bond are at 120° angles.
• alkenes are flat because the atoms in a double bond all lie in the same plane.
• the two groups bonded to each carbon in a triple bond are at 180° angles.
Naming Alkenes
The names of alkenes • use the corresponding alkane name.• change the ending to –ene.
Alkene IUPAC Common
H2C=CH2 ethene ethylene
H2C=CH─CH3 propene propylene
cyclohexene
Ethene (Ethylene)
Ethene or ethylene• is an alkene with the formula
C2H4.• has two carbon atoms connected
by a double bond. • has two H atoms bonded to each
C atom.• is flat with all the C and H atoms
in the same plane.• is used to accelerate the ripening
of fruits.
Naming Alkynes
The names of alkynes • use the corresponding alkane name.• change the ending to –yne.
Alkyne IUPAC Common
HC≡CH ethyne acetylene
HC≡C─CH3 propyne
Naming Alkenes and Alkynes
When the carbon chain of an alkene or alkyne has four or more C atoms, number the chain to give the lowest number to the first carbon in the double or triple bond.
CH2=CH─CH2─CH3 1-butene
1 2 3 4
CH3─CH=CH─CH3 2-butene
1 2 3 4
CH3─CH2─CC─CH3 2-pentyne
5 4 3 2 1
Learning Check
Write the IUPAC name for each of the following:
1. CH2=CH─CH2─CH3
2. CH3─CH=CH─CH3
CH3
|3. CH3─CH=C─CH3
4. CH3─CC─CH3
Solution
Write the IUPAC name for each of the following:
1. CH2=CH─CH2─CH3 1-butene
2. CH3─CH=CH─CH3 2-butene
CH3
|3. CH3─CH=C─CH3 2-methyl-2-butene
4. CH3─CC─CH3 2-butyne
Learning Check
Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH3
CH3
B. CH3─CH2─C=CH─CH3
Solution
Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH3 2-pentyne
CH3
B. CH3─CH2─C=CH─CH3 3-methyl-2-pentene
Cis and Trans Isomers
In an alkene the double bond, • is rigid.• holds attached groups in fixed positions. • makes cis/trans isomers possible.
CH3 CH3 CH3
CH = CH CH = CH
cis trans CH3
In cis-trans isomers• there is no rotation around
the double bond in alkenes.• groups attached to the
double bond are fixed relative to each other.
You can make a “double bond” with your fingers with both thumbs on the same side or opposite from each other.
Cis-Trans Isomers
Two isomers are possible whengroups are attached to thedouble bond are different.• In a cis isomer, groups are
attached on the same side of the double bond.
• In the trans isomer, the groups are attached on opposite sides.
Cis-Trans Isomers
Cis-Trans Isomerism
• Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.
Identical Identical
2-bromopropene 1,1-dibromoethene (not cis or trans) (not cis or trans)
C C
H Br
H CH3
C C
H Br
BrH
H
H
H Br
Cis-Trans Isomers in Nature
• Insects emit tiny quantities of pheromones, which are chemicals that send messages.
• The silkworm moth attracts other moths by emitting bombykol, which has one cis and one trans double bond.
Naming Cis-Trans Isomers
The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers. cis
cis-1,2-dibromoethene trans-1,2-dibromoethene
C C
Br H
BrH
C C
Br Br
H H
33
Learning Check
Name each, using cis-trans prefixes when needed.
C C
CH3 H
CH3H
C C
Br Br
H H
A.
B.
C C
CH3 Cl
ClH
C.
34
Solution
cis-1,2-dibromoethene
trans-2-butene
1,1-dichloropropene
C C
CH3 H
CH3H
C C
Br Br
H H
A.
B.
C C
CH3 Cl
ClH
C.
Addition Reactions
In alkene and alkynes• The double or triple
bond is easily broken, which makes double and triple bonds very reactive.
In addition reactions, reactants are added to the carbon atoms in the double or triple bond.
In hydrogenation, • Hydrogen atoms add to the carbon atoms of a double
bond or triple bond.• A catalyst such as Pt or Ni is used to speed up the
reaction.
Hydrogenation
HC CH + 2H2Ni
HC CH
H H
H H
H2C CH2
H HPt
H2H2C CH2 +
Adding H2 to doublebonds in vegetableoils produces
• Compounds with higher melting points.
• Solids at room temperature such as margarine,
soft margarine, and shortening.
Hydrogenation of Oils
Solution
Write an equation for the hydrogenation of 1-butene using
a platinum catalyst. Pt
CH2=CH─CH2─CH3 + H2 CH3─CH2─CH2─CH3
Trans Fats
In vegetable oils, the unsaturated fats usually containcis double bonds.
• During hydrogenation, some cis double bonds are converted to trans double bonds (more stable) causing a change in the fatty acid structure.
• If a label states “partially” or “fully hydrogenated”, the fats contain trans fatty acids.
Learning Check
(1) True or (2) False
A. ____ There are more unsaturated fats in vegetable oils.
B. ____ Hydrogenation converts some cis-double bonds to
trans- double bonds.
C. ____ Animal fats have more unsaturated fats.
Solution
(1) True or (2) False
A. 1 There are more unsaturated fats in vegetable oils.
B. 1 Hydrogenation of oils converts some cis-double
bonds to trans- double bonds.
C. 2 Animal fats have more unsaturated fats.
Hydration
In the addition reaction called hydration,• an acid H+ catalyst is required.• water (HOH) adds to a double bond.• an H atom bonds to one C in the double bond.• an OH bonds to the other C.
H OH
H+ │ │CH3─CH=CH─CH3 + H─OH CH3─CH─CH─CH3
Hydration
When hydration occurs with a double bond that has anunequal number of H atoms,• the H atom bonds to the C in the double bond with the
more H.• the OH bonds to the C in the double bond with the
fewer H atoms.
OH H H+ │ │CH3─CH=CH2 + H─OH CH3─CH─CH2
Learning Check
Write the product for the hydration of each of the
following:
H+
1. CH3─CH2─CH=CH─CH2─CH3 + HOH
CH3
│ H+
2. CH3─C=CH─CH2─CH3 + HOH
H+
3. + HOH