|
In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is a saturated hydrocarbon. Alkanes consist only of hydrogen and carbon atoms and all bonds are single bonds.〔(【引用サイトリンク】title=Alkane - Definition and More from the Free Merriam-Webster Dictionary )〕 Alkanes (technically, always acyclic or open-chain compounds) have the general chemical formula n2n+2. For example, methane is CH4, in which n=1 (n being the number of carbon atoms). Alkanes belong to a homologous series of organic compounds in which the members differ by a molecular mass of 14.03u (mass of a methanediyl group, —CH2—, one carbon atom of mass 12.01u, and two hydrogen atoms of mass (unicode:≈)1.01u each). There are two main commercial sources: petroleum (crude oil) and natural gas. Each carbon atom has 4 bonds (either C-H or C-C bonds), and each hydrogen atom is joined to a carbon atom (H-C bonds). A series of linked carbon atoms is known as the carbon skeleton or carbon backbone. The number of carbon atoms is used to define the size of the alkane e.g., C2-alkane. An alkyl group, generally abbreviated with the symbol R, is a functional group or side-chain that, like an alkane, consists solely of single-bonded carbon and hydrogen atoms, for example a methyl or ethyl group. The simplest possible alkane (the parent molecule) is methane, CH4. There is no limit to the number of carbon atoms that can be linked together, the only limitation being that the molecule is acyclic, is saturated, and is a hydrocarbon. Waxes include examples of larger alkanes where the number of carbons in the carbon backbone is greater than about 17, above which the compounds are solids at standard ambient temperature and pressure (SATP). Alkanes are not very reactive and have little biological activity. All alkanes are colourless and odourless. Alkanes can be viewed as a molecular tree upon which can be hung the more biologically active/reactive portions (functional groups) of the molecule. ==Structure classification== Saturated hydrocarbons are hydrocarbons having only single covalent bonds between their carbons. They can be: * linear (general formula ) wherein the carbon atoms are joined in a snake-like structure * branched (general formula , ''n'' > 3) wherein the carbon backbone splits off in one or more directions * cyclic (general formula , ''n'' > 2) wherein the carbon backbone is linked so as to form a loop. According to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes. Saturated hydrocarbons can also combine any of the linear, cyclic (e.g., polycyclic) and branching structures; the general formula is , where ''k'' is the number of independent loops. Alkanes are the acyclic (loopless) ones, corresponding to ''k'' = 0. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Alkane」の詳細全文を読む スポンサード リンク
|