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Organic Compounds - Alkanes
Dr. Sean Bonness
Chemistry Department
El Camino College
Organic compounds
• All contain carbon.
• Organic chemistry is the study of carbon
containing compounds.
• The essential needs of daily human life
are food, fuel, shelter, and clothing - all
are organic in nature, except water
(H2O).
Bonding characteristics and Isomerism
• What is the electronic configuration of Carbon
• Mixing of the 2s and 2p orbitals for carbon
produce sp3 hybrid orbitals
• The hybrid orbitals point towards the corners
of a regular tetrahedron. For example
methane (CH4).
Bonding characteristics and Isomerism
(Cont.)
• Carbon atoms bond covalently to other carbon atoms
to form chains or networks.
• A third carbon can join the end of this chain.
• The process can continue to form chains of almost
any length.
Bonding characteristics and Isomerism
(Cont.)
• Carbon can also share more than on pair of
electrons to form multiple bonds
• Structural Isomers - compounds that have the
same molecular formula but in which the atoms
bond in different patterns.
• For example, what are the isomers for the
compound with molecular formula C4H10?
Bonding characteristics and Isomerism
(Cont.)
• What are the structural isomers of C2H6O?
• Structural isomers exert a significant influence on
properties. Ethyl alcohol is a liquid at room temp.,
whereas dimethyl ether is a gas.
• What is a structural isomer of C3H6O?
Functional groups
class
Alkane
Alkene
Alkyne
Functional Expanded Condense
group
structure
d
structure
Name
Functional groups (cont.)
class
Aromatic
Alcohol
Ether
Functional Expanded Condense
group
structure
d
structure
Name
Functional groups (cont.)
class
Amine
Aldehyde
Ketone
Functional Expanded Condense
group
structure
d
structure
Name
Functional groups (cont.)
class
Carboxylic
Acid
Ester
Amide
Functional Expanded Condense
group
structure d structure
Name
Functional Groups (cont.)
• Write condensed structural formulas for the
following compounds.
Alkane structures
• Hydrocarbons - simplest of all organic compounds. Only
contain Carbon and Hydrogen.
• Are called Saturated Hydrocarbons.
• Unsaturated hydrocarbons have double and triple bonds.
Which of the functional groups are unsaturated?
• We also have normal alkanes and branched alkanes, i.e.
butane.
Conformations of alkanes
• Conformations are the different arrangements of atoms in
space achieved by rotation about a single bond.
• Butane
• Ethane
• Are these pairs structural isomers?
Alkane Nomenclature
• Assigning IUPAC names.
• Step 1 - name longest chain.
• Step 2 - number the longest chain
• Step 3 - locate and name attached alkyl groups.
• Step 4 - combine longest chain and alkyl groups into name
Alkane Nomenclature (cont.)
• Step 5 - indicate the number and position of
attached alkyl groups. If two or more alkyl groups,
then use prefixes di, tri, tetra, etc.
Cycloalkanes
• For alkanes the structural formula is CnH2n+2
• Is C3H6 an alkane?
• If form a ring than
• And has the structural formula
Cycloalkanes
Name
cyclopropane
cyclobutane
cyclopentane
cyclohexane
Structural formula
Condensed
formula
Shapes of cycloalkanes
• Stereoisomers are compounds with the same
structural formula but different spatial
arrangements of atoms.
• For example 1,2-dimethylcyclopentane
• Geometric isomers are stereoisomers in which the
geometry of their groups are maintained by rings
and are called cis-trans isomers.
Shapes of cycloalkanes (cont.)
• Show geometric isomers for 1,2dimethylcyclobutane
• What are the geometric isomers for 1,3difluorocyclobutane?
Physical properties of alkanes
• Alkanes are composed of nonpolar carbon-carbon and
carbon-hydrogen bonds.
• Have lower melting points and boiling points than other
organic compounds due to weak attractions. However as
chain length increases, the dispersion forces increases and
which is why very long chain structures are solids (see
figure 11.18 in S&S text)