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Organic Chemistry
Chemistry of Carbon Compounds
(except oxides, carbides, &
carbonates)
Why so many C compounds?
• Carbon atoms can bond with other carbon
atoms in chains, rings, and networks.
• Bonds are covalent.
Lewis Diagram of C
•
•C•
•
Carbon has 4 unpaired electrons.
It can form 4 covalent bonds.
Note: C can form only 3 bonds to any other
single C atom.
Bonding Capacity of H, O, etc.
• H can form only 1 bond.
• O and S like to form 2 bonds.
• The halogens (F, Cl, Br, I) form only 1
bond.
• N and P form 3 bonds.
Properties of Covalent
Substances
•
•
•
•
•
•
(also called molecular substances)
Low melting & boiling points
Poor conductors of heat & electricity
May be soft or brittle
Generally nonpolar – van der Waals forces
Tend to dissolve in nonpolar solvents
React more slowly than ionic compounds
Chemical Formulas
• show kind & number of atoms.
CH3OH
CH4
CH2Cl2
CH3Cl
Structural Formulas
• Show kind & number of atoms.
• Also show bonding patterns and approximate
shapes of molecules.
• 2-D rep of 3-D object so structural formulas
aren’t totally realistic.
H
H–C–H
H
Structural Formulas
• – A single line represents one pair of
electrons (a single bond).
• = A double line represents two pairs of
electrons (a double bond).
•  A triple line represents three pairs of
electrons (a triple bond).
Shape
• The 4 unpaired electrons around the C
atom are located at the corners of a
tetrahedron.
• 109.5 apart.
Vocabulary Interlude
• Saturated: organic compounds
containing only Single bonds.
• Unsaturated: organic compounds
containing one or more double or
triple bonds.
Vocabulary
• Hydrocarbons: organic compounds
containing only C and H.
• Homologous Series: a group of
compounds with related structures and
properties. Each member of the series
differs from the one before it by the
same additional unit.
Homologous Series
• The molecules have a fixed, numerical
relationship among the numbers of atoms.
Condensed Structural Formula
• Shows kind & number of atoms
• Shows some structural information, but not
all the details. Fits on 1 line of type.
H H H
H–C–C–C–H
H H H
Becomes
CH3CH2CH3
Alkanes
• Homologous series of saturated hydrocarbons.
• Release energy when burned.
CH4
H
H–C–H
H
C2H6
H H
H–C–C–H
H H
• C2H6 is also written CH3CH3
Space-filling model
Above: 3 representations of CH4. Below: Ball
and stick model of ethane.
Alkanes or CnH2n+2
• C3H8
Chemical
Formula
CH3CH2CH3
Condensed Structural
Formula
H H H
H–C–C–C–H
H H H
Structural
Formula
Ball & stick
model of
propane.
Bond angles =
109.
th
4
straight-chain alkane
C4H10
H H H H
H–C–C–C–C–H
H H H H
Or CH3CH2CH2CH3
Ball and Stick model of butane.
Alkanes: base unit
CH4
CH3CH3
or C2H6
CH3CH2CH3
or C3H8
CH3CH2CH2CH3
or C4H10
CH3CH2CH2CH2CH3
or C5H12
Difference between each is CH2
Naming straight-chain Alkanes
• Name describes molecule so you
can draw it.
• All alkanes have the suffix –ane.
• The prefix depends on the number
of C’s.
Prefix
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
# of C atoms
1
2
3
4
5
6
7
8
9
10
Formula
CH4
C2H6
C3H8
C4H10
C5H12
Name
Meth + ane
Ethane
Propane
Butane
Pentane
Properties of Alkanes
• Change systematically with number of C’s
• As the number of C’s increases, the boiling
point increases.
– The molecules get heavier & harder to change
into the gas phase.
Properties of Alkanes
•
•
•
•
•
•
Low Reactivity
Except readily undergo combustion – fuels
Nonpolar – Don’t dissolve well in water.
Low melting pts & boiling pts.
(M.P. & B.P. increase with molecular mass)
High vapor pressures
Which property is generally
characteristic of an organic compound?
A.
B.
C.
D.
Low melting point
High melting point
Soluble in polar solvents
Insoluble in nonpolar solvents
Correct response = A
Which of the following compounds
has the highest boiling point?
A.
B.
C.
D.
CH4
C2H6
C3H8
C4H10
Correct answer = D. In nonpolar covalent compounds, the
boiling point depends on the strength of the van der Waals
interactions. The van der Waals forces increase as the size
of the molecule increases. (Bigger molecule, bigger
electron cloud.)
Branched-chain alkanes
• Beginning with butane, C4H10, there is more
than 1 way to arrange the atoms.
H
H–C–H
H H
H–C–C–C–H
H H H
Branched alkane.
Can’t link all the
C’s without lifting
pencil off the
paper.
Methyl propane
Isomers
• Compounds with the same molecular formula
but different structural arrangement.
• The more C atoms there are in the formula,
the more isomers there will be.  More
possible ways to arrange them.
Isomers
• Different structures, different
properties.
• Isomers have different chemical
and physical properties.
A note about isomers --• If you are comparing 2 structural formulas
& you can superimpose them, they are not
isomers – they are the same molecule!
• If you can rotate or flip one of the structural
formulas & then superimpose it on the other
one, they are not isomers – they are the
same molecule!
These diagrams
represent the
same molecule.
Represents bond to H
These diagrams
represent the
same molecule.
Represents bond to H
These diagrams
represent the
same molecule.
Represents bond to H
Two different
molecules!
Represents bond to H
Naming Branched-Chain Alkanes
• The goal of the name is to describe the
molecule so you can draw it.
Naming branched-chain alkanes
• Find the longest continuous chain or backbone of
C atoms. (Bends don’t count!)
• The base name is derived from the number of C’s
in the longest chain.
• Branches are named in the prefix. Branches are
also named by the number of C atoms. The
“branch” part of the name ends in “yl.”
• The location of the branch is shown by assigning
numbers to the C’s in the backbone. Number from
the end that gives the lowest number for the
branch.
• There may be more than 1 of the same type of
branch. Use di, tri, etc.
H
H–C–H
H H
H–C–C–C–H
H H H
Longest continuous
chain has 3 carbon
atoms – propane.
Branch has 1 carbon – methyl.
Branch has to be at C-2.
(Only give the number if
necessary.)
Methyl propane
C4H10
CH3CH(CH3)CH3
H
H–C–H
H–C–H
HH H
H–C–C–C–C–H
H H
H
H–C–H
H
Longest continuous chain has 6
carbon atoms. It’s a hexane.
Branch is 1 carbon long – methyl.
Branch is located at C-2.
2-methyl hexane
C7H16
CH3CH(CH3)CH2CH2CH2CH3
A note about branches
• If you have several branches with the same
# of C atoms, you can condense the name a
little.
• 2-methyl 3-methyl pentane becomes 2,3dimethyl pentane.
• The # of numbers must match the # of
branches.
H
H–C–H
H H H
H– C–C–C–C–H
H
H
H–C–H H–C–H
H
H
Longest continuous chain has
6 carbon atoms: hexane
Branch is 1 carbon long:
methyl
Branch is located at C-3
3-methyl hexane
C7H16
CH3CH2CH2CH(CH3)CH2CH3
CH3(CH2)2CH(CH3)CH2CH3
Alkenes
• Another homologous series of hydrocarbons.
• Each member contains one double covalent
bond between C atoms.
So alkenes are unsaturated.
• General formula = CnH2n
Naming Alkenes
• Names: # of C’s in parent chain gives
prefix. Suffix = -ene.
1st member is C2H4, ethene.
H
H
C=C
H
H
Alkenes with 4 or more C’s
• Number C atoms.
• Use lowest possible # to specify location of
1st C in double bond.
Naming Alkenes
• Number C atoms in backbone. Give double
bond the lowest possible number.
1-butene
H
HH
C=C–C–C–H
H H H H
2-butene
H H HH
H–C–C=C–C–H
H
H
C4H8
C4H8
CH2CHCH2CH3
CH3CHCHCH3
Naming Branched-Chain Alkenes
• Parent chain = longest chain that contains
the double bond.
• Also, position of double bond, not branches,
determines numbering of backbone.
• Give 1st C in bond lowest possible #.
Properties of Alkenes
• Nonpolar – low solubility in H2O
• Fairly low M.P. & B.P.
• More reactive than alkanes – double bond =
site of reactivity.
Alkynes
•
Homologous series of unsaturated
hydrocarbons that contain one triple bond.
•
Each member contains one triple carboncarbon bond.
–
•
Alkynes are unsaturated.
General formula = CnH2n-2
Naming Alkynes
• Name: Prefix depends on # of C’s. Suffix
= -yne.
• If necessary, number the 1st carbon atom at
which the triple bond occurs.
H–CC–H
C2H2
ethyne
H
H–CC–C–H
H
C3H4
propyne
CHCCH3
1-butyne
CHCCH2CH3
HH
H–CC–C–C–H
HH
C4H6
H
H
H–C–CC–C–H
H
H
C4H6
2-butyne
CHCH
CH3CCCH3
3 Homologous Series of HC’s
Name of Series
General Formula
Ending
Alkanes
CnH2n+2
-ane
Alkenes
CnH2n
-ene
Alkynes
CnH2n-2
-yne
Which compound belongs to the
alkene series?
A.
B.
C.
D.
C2H2
C2H4
C6H6
C6H14
Correct answer = B. Alkenes follow
the format CnH2n. A & C are CnHn.
D is CnH2n+2.
In which group could the
hydrocarbons all belong to the same
homologous series?
A.
B.
C.
D.
C2H2, C2H4, C2H6
C2H4, C3H4, C4H8
C2H4, C2H6, C3H6
C2H4, C3H6, C4H8
Correct answer = D. Members of a homologous series
all have the same relationship between the atoms.
Every compound in set D fits the formula CnH2n.
Which of the following is a
saturated hydrocarbon?
A.
B.
C.
D.
Ethene
Ethyne
Propene
Propane
Correct answer = D. The alkanes are
saturated.