ALKANES
HYDROCARBONS
HISTORY OF ORGANIC
Early 19th century chemists were only familiar with inorganic,
ionic compounds.
They were baffled by the fact that several compounds that
were found in fruits and vegetables were composed of many
carbon, hydrogen, nitrogen and oxygen atoms in different
combinations were stable.
The “vital force theory” grew out of the idea that these
molecules could only come from living organisms.
In 1828, Wohler did an experiment that destroyed this
idea…he made urea from ammonia and cyanic acid.
Now, we know that there are virtually a limitless number of
organic compounds that can be synthesized.
ORGANIC
COMPOUNDS
Properties of organic substances are related to their
structure. Most compounds contain carbon, hydrogen and
any of the other following elements: oxygen, nitrogen,
phosphorus, sulfur and the halogens.
Many of these atoms follow typical bonding patterns:
C has 4 bonds and no lone pairs.
N has 3 bonds and 1 lone pair.
O and S have 2 bonds and 2 lone pairs.
H has 1 bond and no lone pairs
Halogens (F, Cl, Br, I) have 1 bond and 3 lone pairs.
HYDROCARBONS
2 categories:
1) Aromatic- compounds with carbon and hydrogen that
contain benzene rings
2) Aliphatic- compounds with carbon and hydrogen that are
not aromatic (alkanes, alkenes, alkynes, and
cycloalkanes)
Benzene
ALKANES
Alkane is the term used for saturated hydrocarbons, meaning
that no multiple bonds exist between carbons.
These molecules are nonpolar, due to electronegativity
differences.
Weak intermolecular forces exist, and so these molecules
have relatively low boiling points.
Typical alkanes follow this pattern for formulas:
CnH2n+2
ISOMERS
In some cases, it is possible to draw molecules with 2
different structures that have the same chemical formula.
That is an isomer, by definition.
Isomers are common among organic compounds.
Examples:
n-butane and isobutane
IUPAC NAMING
IUPAC stands for International Union of Pure and Applied
Chemistry.
This group of professional chemists set guidelines for
naming chemical compounds.
Different naming procedures are used for organic molecules
than what are used for inorganic compounds.
In order to name compounds, it is important to recognize
many common alkyl groups.
Alkyl refers to a group with one less hydrogen than an alkane
(CnH2n+1).
IUPAC NAMING
Three prefixes used commonly indicate structural info:
Iso- has this structure at one end of a carbon chain
Sec- (for secondary)
Tert- or t- (for tertiary)
PRIMARY, SECONDARY
AND TERTIARY
Primary (1°) refers to a carbon that is bonded to 1 other
carbon.
Secondary (2°) refers to a carbon that is bonded to 2 other
carbons.
Tertiary (3°) refers to a carbon that is bonded to 3 other
carbons.
ALKYL GROUPS
RULES FOR NAMING
ALKANES
1)
Select the longest continuous chain of carbon atoms as the parent
compound, and consider all alkyl groups attached to it as branch
chains that have replaced hydrogen atoms of the parent
hydrocarbon. (The name of the alkane consists of the name of the
parent compound prefixed by the alkyl groups attached to it.)
2)
Number the carbon atoms in the parent carbon chain from one end
to the other starting with the end closest to the first carbon atom
that has a branch chain.
3)
Name each branch-chain alkyl group and designate its position on
the parent carbon chain by a number.
4)
When the same branch alkyl group occurs more than once,
indicate this by a prefix (di, tri, tetra, etc) written in front of the
alkyl group name.
5)
The numbers indicating the carbons that the groups are on are
separated by commas, then a hyphen in front of the group name.
SUMMARY
1) Find the longest chain! Be sure to check groups
attached…they may be part of the main chain!
2) Number the carbons from the end where an attached
group is nearest.
3) Use numbers to tell which carbon the group is attached
to.
4) Use prefixes if there are more than one of the same
group.
5) Always list branches in alphabetical order.
REACTIONS OF
CARBON
1) Oxidation-reduction reactionWhen carbon atoms are oxidized (lose electrons), they often
form additional bonds to oxygen.
When carbon atoms are reduced, they often form additional
bonds to hydrogen.
2) Substitution reaction-
Many involve halogens…
Methane gas plus bromine liquid
REACTIONS OF
CARBON
3) Elimination reactionsSingle reactant is split into two products, and one is
eliminated.
These reactions form multiple bonds.
4) Addition reactions- reverse of an elimination reaction…two
reactants come together to form one product