The primary source of alkanes is petroleum Natural gas consists chiefly of methane, but ethane, propane, butane, and isobutane are also present. Petroleum is a complex mixture of hydrocarbons that must be refined into different fraction before it can be used

Cycloalkanes with only one ring are named by attaching the prefix cyclo- to the names of the alkanes possessing the same number of carbon atoms

The different arrangements of atoms caused by rotation about a single bond are called conformations (构象)of the molecule, and a specific conformation is called a conformer (构象异构体, conformation isomer). An analysis of the energy changes that a molecule undergoes as groups rotate about single bonds is called a conformational analysis (构象分析)

An equimolar mixture of two enantiomers is called a racemic form (either a racemate or a racemic mixture). A racemic form shows no rotation of plane￾polarized light

Before 1951 only relative configurations of chiral molecules were known. Configurations of chiral molecules were related to each other through reactions of known stereochemistry. The standard compound was glyceraldehyde

The C—X bond of alkyl halides is polarized. The carbon atom bears a partial positive charge, The halogen atom a partial negative charge

SN2 reactions are highly useful in organic synthesis because they enable use to convert one functional group into another —— functional group transformation (functional group interconversion)

In the addition of HX to an unsymmetrically substituted alkene, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms and that the X group adds to the carbon having more alkyl substituents. Markovnikov’s rule can be restated by saying that, in the addition of HX to an alkene, the more stable carbocation intermediate is formed

There is a group of compounds in which carbon forms only two bonds. These neutral divalent carbon compounds are called carbenes. Most carbenes are highly unstable compounds that are capable of only fleeting existence. Soon after carbenes are formed they usually react with another molecule

These spectra are often called carbon magnetic resonance (CMR) spectra or 13C NMR spectra. In some important ways 13C spectra are usually les complex and easier to interpret than proton (1H) NMR spectra