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Hydrocarbons
The basis for organic chemistry
Organic Compounds
• Contain C bonded to other elements,
commonly H, O, N, S, and halogens
• Carbon
– Can form many different compounds due to its
hybrid orbitals
– Has intermediate electonegativity, so its most
likely to form molecular compounds (Recall:
molecular compounds have diverse properties)
– Can make single, double, and triple bonds
– Can form isomers (same molecular formula but
different arrangement of atoms)
Types of Hydrocarbons
• Saturated: Contain the maximum number of
hydrogens, single bonds between all carbons
• Unsaturated: Contain 1+ double or triple
bonds
Types of Hydrocarbons
• Aliphathic Carbons are arranged in chains
• Cyclic: Carbons are arranged in rings
• Aromatic: Contain a benzene ring
Benzene Ring
• Does not act as 3 single bonds and 3 double
bonds
• It’s 6 identical bonds of intermediate length
• Due to hybridization (delocalized, shared
electrons)
Types of Hydrocarbons
Name
Alkane
Alkene
Alkyne
Definition
Hydrocarbon with only
single bonds between
carbon atoms.
Hydrocarbon with at
least one double bond.
Hydrocarbon with at
least one triple bond.
General
Formula
C2H2n+2
C2H2n
C2H2n-2
Naming Alkanes
Based off the number of C atoms in the
longest chain
1. Count the number of C’s in the longest chain
2. Determine the appropriate root
3. Add the suffix “ane”
Hydrocarbon Root Names
# of Carbons
1
2
3
4
5
6
7
8
9
10
Root Name
methethpropbutpenthexheptoctnondec-
Structural Shorthand
Explicit hydrogens (those required to complete
carbon’s valence) are usually left off of
drawings of hydrocarbons
CH3
H3C
H
H
H
C1 C2 C3 C4
H
H
H
H
H
H
H
C1 C2 C3
C4
Line intersections represent carbon atoms
Rules for Naming Alkanes
(Nomenclature)
For a branched hydrocarbon, the longest continuous chain
of carbon atoms gives the root name for the hydrocarbon
H3C1
2
H3C
3
4
CH3
4 carbon chain = butane
Naming Branched Alkanes
Based off the number of C atoms in the
longest chain
1. Count the number of C’s in the longest chain,
and number the chain so that the lowest
possible number is given to the first branching
location.
2. Determine the appropriate root
3. Use the numbered C’s to give the branches a
position number add “yl” suffix
4. Add the suffix “ane” if all single bonds
Naming Branched Alkanes
Important Rules:
1. If there is more than one type of branch, name
the branches in alphabetical order (irrespective
of any prefix)
2. If there is more than two of the same type of
branch, give the branch a position number and
prefixes “di”, “tri” “tetra” etc.
3. Put commas between numbers and
hyphens between numbers and letters
Rules for Naming Alkanes
(Nomenclature)
When alkane groups appear as substituents, they
are named by dropping the -ane and adding -yl.
—CH3 Methyl
—CH2CH3 Ethyl
—CH2CH2CH3 Propyl
—CH2CH2CH2CH3 Butyl
H3C
H3C
Methyl
CH3
Rules for Naming Alkanes
(Nomenclature)
The positions of substituent groups are specified
by numbering the longest chain of carbon atoms
sequentially, starting at the end closest to the
branching.
H3C1
2
3
H3C
Methyl
4
CH3
Rules for Naming Alkanes
(Nomenclature)
The location and name of each substituent are
followed by the root alkane name. The substituents
are listed in alphabetical order (irrespective of any
prefix), and the prefixes di-, tri-, etc. are used to
indicate multiple identical substituents.
H3C1
2
3
H3C
Methyl
4
CH3
Name: 2-methylbutane
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
CH3
6
7
9 carbons = nonane
8
H3C9
Step #1: For a branched hydrocarbon, the longest
continuous chain of carbon atoms gives the root name
for the hydrocarbon
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
CH3
6
7
8
9 carbons = nonane
CH3 = methyl
chlorine = chloro
H3C9
Step #2: When alkane groups appear as substituents, they
are named by dropping the -ane and adding -yl.
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
6
7
9 carbons = nonane
CH3
CH3 = methyl
chlorine = chloro
8
H3C9
1
9 NOT
9
1
Step #3: The positions of substituent groups are
specified by numbering the longest chain of carbon
atoms sequentially, starting at the end closest to the
branching.
Nomenclature Practice
Name this compound
CH3
H3C1 2
Cl
3 4
5
CH3
6
7
9 carbons = nonane
CH3 = methyl
8
chlorine = chloro
H3C9
2-chloro-3,6-dimethylnonane
Step #4: The location and name of each substituent are
followed by the root alkane name. The substituents are
listed in alphabetical order (irrespective of any
prefix), and the prefixes di-, tri-, etc. are used to
indicate multiple identical substituents.
• Try the examples on the sheet!
Naming Alkenes & Alkynes
1. Count the number of C’s in the longest chain
containing the double/triple bond.
•
•
This is the parent chain, determine the root
Number the parent chain so that the double/triple bond has the
lowest possible position number
2. Identify the position numbers of branches
•
Same rules as before
3. Write the branches in alphabetical order
4. Write the root, including a number that identifies
the position of the double/triple bond
5. Add the suffix “ene” or “yne”
Naming Alkenes & Alkynes
Cyclic Alkanes
Cyclopropane, C3H6
Cyclobutane, C4H8
Cyclopentane, C5H10
Cyclohexane, C6H12
Cycloheptane, C7H14
Remember, explicit hydrogens are left out
Naming Cyclic Hydrocarbons
1. Number the carbons in the ring, in either direction, so
that the multiple bond is between the two lowest
numbers, and the branches get the lowest possible
position numbers.
2. Identify branches.. Prefixes are the same di, tri,
prop etc. and are written alphabetically.
3. The root is –cyclo- plus the name for the number of
carbon atoms in the ring.
4. The suffix is –ane for cycloalkanes –ene for
cycloalkenes and –yne for cycloalkynes.
Naming Cyclic Hydrocarbons
Naming Aromatics
•
Contains benzene:
•
•
•
Same rules apply
If benzene is the parent chain “benzene” suffix
If benzene is a branch group “phenyl”
Naming Aromatic
Hydrocarbons
• Practice!!
Properties of Hydrocarbons
• Made up of mostly C and H
• Relatively nonpolar
– Low solubility in polar solvents (e.g. water)
– Good solvents for other nonpolar molecules
• Mostly london-dispersion forces (weak)
– Low boiling and melting points
Reactivity of Hydrocarbons
• Alkanes are generally less reactive than
alkenes or alkynes
• Aromatic compounds are more reactive
than alkanes, but less reactive than alkenes
and alkynes.
Alkanes < aromatics < alkenes < alkynes
Reactions of Hydrocarbons
Combustion:
– Hydrocarbons burn readily in air to produce
carbon dioxide and water.
C3H8(g) + 5 O2(g) --> 3CO2(g) + H2O(g)
Incomplete Combustion:
– Produces carbon and poisonous carbon
monoxide.
C3H8(g) + 7/2 O2(g) --> C(s) + CO(g) CO2(g) + 4 H2O(g)
Reactions of Alkanes
• Single bonds between carbon atoms
are difficult to break. (This is why
alkanes are relatively unreactive)
• Can undergo combustion reactions and
substitution reactions
Reactions of Alkanes
Substitution Reactions:
• Hydrogen atoms may be substituted by a halogen.
• The product is a halogenated alkane (alkyl halides)
Reactions of Alkenes and
Alkynes
Addition Reactions:
• Reactions in which a molecule is added to a double
or triple bond.
• No loss of hydrogen atoms from the hydrocarbon
Types of Addition reactions
Markovnikov’s Rule
• “The rich get richer”
• When a hydrogen halide is added to an alkene or alkyne,
the hydrogen atom bonds to the carbon atom that
already has more hydrogen atoms.
Carbon 1 has 2 H’s
Carbon 2 has 1 H
Reactions of Aromatic
Hydrocarbons
• Less reactive than alkenes and do not
undergo addition reactions unless under
conditions of extreme temperature or
pressure
• Do undergo substitution reactions (more
reactive than alkanes)