3. Alkanes and Cycloalkanes
What are Alkanes?
- A hydrocarbon is a compound composed of only carbon and hydrogen. Alkanes are saturated hydrocarbons;
they only contain carbon-carbon single bonds. Alkanes are often referred to as aliphatic hydrocarbons, because
the physical properties of the higher members of this class resemble those of the long carbon-chain molecules we
find in animal fats and plant oils. Alkenes are unsaturated hydrocarbons with one or more carbon-carbon double
bonds; alkynes are unsaturated hydrocarbons with one or more carbon-carbon triple bonds; and arenes are
unsaturated hydrocarbons with one or more benzene like rings.
Line-angle formulas are an abbreviated way to
draw structural formulas in which each line ending represents a carbon atom and a line represents. Alkanes have
the general molecular formula C
What is Constitutional Isomerism in Alkanes
- Constitutional isomers are compounds that have the same molecular formula, but different structural formulas.
They differ in the kinds of bonds they have or in their connectivity.
How Do We Name Alkanes
- The IUPAC name of an alkane with an unbranched chain of carbon atoms consists of two parts: a prefix that
indicates the number of carbon atoms in the chain and the ending –ane to show that the compound is a saturated
(meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non-, dec-, undec, dodec, tridec, tetradec,
pentadec, dexadec, heptadec, octadec, nonadec, eicos- ) The IUPAC name of an alkane with a branched chain
consists of a parent chain that indicates the longest chain of carbon atoms in the compound and the substituent
names that indicate the groups bonded to the parent chain. A substituent group derived from an alkane by the
removal of a hydrogen atom is called an alkyl group and is commonly represented by the symbol R-. We name
the alkyl groups by dropping the –ane from the name of the parent alkane and adding the suffix –yl.
- The prefix sec- is an abbreviation for secondary, meaning a carbon bonded to two other carbons. The prefix tert-
is an abbreviation for tertiary, meaning a carbon bonded to three other carbons. Give each substituent on the
parent chain a number, when naming number the parent chain from the end that gives the lowest numbers. If
there are two or more identical substituents, number the parent chain from the end that gives the lower number to
the substituent encountered first. The number of times a substituent occurs is indicated by the prefix, di-, tri-,
tetra-, penta-, hexa-, etc. if there are two or more different substituents list them in alphabetical order, and
number the chain from the end that gives the lower number to the substituent encountered first.
The prefixes are
not included in alphabetizing, alphabetize the names of the substituents first then insert prefix.
- For alkanes beond propane, iso indicates that one end of an otherwise unbranched chain terminates in a