Part II. HYDROCARBONS

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.