Chapter 7
SATURATED HYDROCARBONS
7.1. Classification, isomerism, and nomenclature
Saturated hydrocarbons are compounds consisting only of sp3-hybridized carbon and hydrogen atoms.
Alkanes is the generic name of saturated hydrocarbons. According to the carbon skeleton structure, they are divided into proper alkanes and cycloalkanes that have a closed chain of carbon atoms. Due to a number of common properties of alkanes and cycloalkanes (except for cycles containing 3-4 carbon atoms), both hydrocarbon types are discussed together.
Alkanes are divided into unbranched (linear, or normal) and branched ones. Cycloalkanes are classified according to the following structural signs:
• number of carbon atoms in a cycle;
• number of cycles in a molecule;
• mode of cycle bonding (if several cycles are present in the molecule). Monocyclic hydrocarbons are the simplest ones; depending on the cycle size, they
are divided into small (С3 and С4), normal (С5-С7), medium cycles (С8-С11), and macrocycles (12 and more carbon atoms).
Structures consisting of two and more cycles are bicyclic and polycyclic ones, respectively. Examples of such compounds include the bicyclic hydrocarbon decahydronaph-thalene, tricyclic hydrocarbon adamantane, and tetracyclic gonane (parent hydrocarbon of steroids). °nly monocyclic hydrocarbons will be discussed in this chapter.
Alkanes may contain asymmetric carbon atoms, leading to the emergence of stereoisomers. Two out of nine constitutional (structural) isomers of heptane С7Н16 contain an asymmetric carbon atom, and each of these chiral heptanes exists as a pair of enantiomers, i.e., configurational isomers.
Alkanes with two asymmetric centers (e.g., 3,4-dimethylhexane) can also exist as diastereomers.