1 introduction to organic chemistry organic chemistry is the study of compounds that contain the...
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Introduction to Organic Chemistry
Organic chemistry is the study of compounds thatcontain the element carbon.
• Organic chemicals affect virtually every facet of our lives.
• Products such as clothes, foods, medicines, gasoline, refrigerants, and soaps are composed almost solely of organic compounds.
• Because organic compounds are composed of covalent bonds, their properties differ a great deal from those of ionic inorganic compounds.
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1. All organic compounds contain carbon atoms and most contain hydrogen atoms.
• Carbon has four valence electrons available for bonding.
• Hydrogen has a single valence electron and can only form single bonds.
Characteristic Features of Organic Compounds
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2. Carbon forms single, double, and triple bonds toother carbon atoms.
Characteristic Features of Organic Compounds
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3. Some compounds have chains of atoms and somecompounds have rings.
Characteristic Features of Organic Compounds
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4. Organic compounds may also contain elements other than carbon and hydrogen.
• Any atom that is not carbon or hydrogen is called a heteroatom.
• Each heteroatom forms a characteristic number of bonds, determined by its location in the periodic table.
• The common heteroatoms (N, O, F, Cl, Br, and I) also have nonbonding, lone pairs of e−, so that each atom is surrounded by eight electrons.
# of bonds + # of lone pairs = 4
Characteristic Features of Organic Compounds
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Characteristic Features of Organic Compounds
4. Organic compounds may also contain elements other than carbon and hydrogen, (heteroatoms )
Each heteroatom forms a characteristic number of bonds, determined by its location in the periodic table.
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The most common multiple bond between carbonand a heteroatom is a carbon–oxygen double bond.
Characteristic Features of Organic Compounds
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Drawing Organic MoleculesCondensed Structures
In a condensed structure, all of the atoms are drawn in,but the two-electron bond lines and lone pairs on heteroatoms are generally omitted.
• A carbon bonded to 3 Hs becomes CH3.• A carbon bonded to 2 Hs becomes CH2.
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Drawing Organic MoleculesCondensed Structures
• Sometimes structures are further simplified by using parentheses around like groups.
• Two CH2 groups bonded together become (CH2)2. • Two CH3 groups bonded to the same carbon become (CH3)2C.
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Drawing Organic MoleculesSkeletal Structures
When drawing a skeletal structure:
• Assume there is a carbon atom at the junction of any two lines or at the end of any line.
• Assume there are enough hydrogens around each carbon to give it four bonds.
• Draw in all heteroatoms and the hydrogens directly bonded to them.
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Drawing Organic MoleculesSkeletal Structures
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Functional Groups
• A functional group is an atom or group of atoms with characteristic chemical and physical properties.
• A functional group contains a heteroatom, a multiple bond, or sometimes both.
• The letter R is used to abbreviate the carbon and hydrogen portion of a molecule.
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Functional GroupsHydrocarbons
Hydrocarbons are compounds that contain only carbon and hydrogen.
• Alkanes have only C–C single bonds and no functional group.
• Alkenes have a C–C double bond as their functional group.
• Alkynes have a C–C triple bond as their functional group.
• Aromatic hydrocarbons contain a benzene ring, a six-membered ring with three double bonds.
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Functional GroupsCompounds Containing a C=O group
• Carbonyl groups (carbon–oxygen double bonds) are present in several different compounds.
Functional groups
. Alkanes
CH3 CH3
Alkenes
CH2 CH2
Alkynes
CH CH
Alcohols
CH3 CH2 OH
Ethers
CH3 O CH3
Thiols
CH3 CH2 SH
Aldehydes
CH3 C
O
H
Ketone
CH3 C
O
CH3
Organic acids
CH3 C
O
O H
CH3 C
O
O CH3
Esters Amines
CH3 NH2 CH3 C
O
NH2
Amides
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AlkanesIntroduction
Alkanes are hydrocarbons having only C–C and C–H single bonds.
• Alkanes that contain chains of C atoms but no rings are acyclic alkanes and have the general formula CnH2n+2.
• Acyclic alkanes are called saturated alkanes because they have the maximum number of H atoms per C atom.
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AlkanesIntroduction
• Cycloalkanes contain C atoms joined in one or more rings.
• They have the general formula CnH2n.
All alkane molecules have names that end in the suffix “-ane.”
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Simple AlkanesAcyclic Alkanes Having
Fewer than Five Carbons
• Methane is a one-carbon alkane.
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Simple AlkanesAcyclic Alkanes Having
Fewer than Five Carbons
• Ethane is a two-carbon alkane.
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Simple AlkanesAcyclic Alkanes Having Fewer than Five Carbons
• Propane is a three-carbon alkane.
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Simple AlkanesAcyclic Alkanes Having
Fewer than Five Carbons
• The following two representations of propane are equivalent:
• The bends in a carbon chain don’t matter when it comes to identifying different compounds.
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Simple AlkanesAcyclic Alkanes Having
Fewer than Five Carbons• Butane has four-carbon atoms in a row. It is a straight-chain alkane.
• Isobutane has three carbon atoms in a row and one bonded to the middle. It is a branched-chain alkane.
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Simple AlkanesAcyclic Alkanes Having Fewer than Five Carbons
• Butane and isobutane are isomers of each other.
• Isomers are two different compounds with the same molecular formula.
• Constitutional isomers differ in the way the atoms are connected to each other.
• Another example of constitutional isomers:
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Simple AlkanesAcyclic Alkanes Having Five or More Carbons
• As the number of C atoms increases, the number of possible isomers increases.
• Pentane is a five-carbon alkane with three isomers:
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Simple AlkanesAcyclic Alkanes Having Five or More Carbons
• After pentane, the following names apply:
# of C’s Name Structure
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hexane CH3CH2CH2CH2CH2CH3
heptane CH3CH2CH2CH2CH2CH2CH3
octane CH3CH2CH2CH2CH2CH2CH2CH3
nonane CH3CH2CH2CH2CH2CH2CH2CH2CH3
decane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
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An Introduction to NomenclatureThe IUPAC System of Nomenclature
• IUPAC stands for International Union of Pure and Applied Chemistry.
• The IUPAC system of nomenclature provides a system of naming organic compounds.
• Using the IUPAC system, each organic compound gets an unambiguous name.
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Alkane NomenclatureNaming Substituents
• Carbon substituents are called alkyl groups.
• An alkyl group is formed by removing 1 H from an alkane.
• To name an alkyl group, change the “-ane” ending of the parent alkane to “-yl.”
• Each alkyl group has a bond that can then be attached to something else.
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Alkane NomenclatureNaming Substituents
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Alkane NomenclatureNaming Substituents
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Alkane NomenclatureNaming an Acyclic Alkane
• The longest chain may not be written horizontally.
• All three examples below have 6 Cs in their longest chain:
HOW TO Name an Alkane Using the IUPAC System
• It does not matter if the chain is straight or has bends.
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Alkane NomenclatureNaming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
Step [1] Find the parent carbon chain and add the suffix.
• Find the longest continuous carbon chain, and name it with an “-ane” ending.
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Alkane NomenclatureNaming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
Step [2] Number the atoms in the carbon chain togive the first substituent the lower number.
CORRECT INCORRECT
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Alkane NomenclatureNaming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
• The following compound contains two methyl groups, so we use the name dimethyl for them.
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Alkane NomenclatureNaming an Acyclic Alkane
Sample Problem 10.9
Give the IUPAC name for the following compound.
CH3 C CH2CH2 C C CH2CH3
CH3
CH3H H
HCH3CH2
longest chain is 8 Cs = octane1 2 5 6
CH3methyl atC2
CH3 methyl at C6
CH3CH2ethyl at C5
Answer
5-ethyl-2,6-dimethyloctane
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CycloalkanesNaming Cycloalkanes
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CycloalkanesNaming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
Step [1] Find the parent cycloalkane.
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CycloalkanesNaming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
Step [2] Name and number the substituents.
• No number is needed for a cycloalkane with a single substituent.
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CycloalkanesNaming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
For rings with two or more substituents:
• begin numbering at one substituent
• then, proceed around the ring to give the second substituent the lower number
For two different substituents, number the ring toassign the lower number to the substituentsalphabetically.
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CycloalkanesNaming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
Earlier letter = lower number
ethyl group at C1
methyl group at C3
1-ethyl-3-methylcyclohexane(not 3-ethyl-1-methylcyclohexane)
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Physical Properties
• Alkanes contain only nonpolar C–C and C–H bonds.
• Alkanes exhibit only weak intermolecular forces, so they have low melting points and boiling points.
• Smaller alkanes are gases at room temperature, whereas larger alkanes are liquids.
• Alkanes are less dense than water, meaning that they will float on the surface of water.
• Alkanes are insoluble in water.
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• As the number of carbons in an alkane increases, the boiling point increases:
Physical Properties
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Combustion
• Alkanes have no functional group, so they undergo few reactions.
• Combustion is the only reaction of alkanes in this chapter. It is an oxidation reaction.
• In the combustion reaction, alkanes burn in the presence of O2 gas to form CO2 and H2O.
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Combustion
• The products, CO2 + H2O, are the same, regardless of the identity of the alkane that undergoes combustion.
• Combustion of alkanes in the form of natural gas, gasoline, or heating oil releases energy for heating homes, powering vehicles, and cooking food.
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Combustion
• If there is not enough O2 to react, incomplete combustion may occur, and carbon monoxide (CO) is formed instead of carbon dioxide (CO2).
• Carbon monoxide is a poisonous gas that binds to hemoglobin in blood, thereby reducing the amount of O2 that can be transported to cells.