Alkane nomenclature Alkanes represent the simplest of the functional groups which are common in organic chemistry. An alkane contains only carbon and hydrogen(a hydrocarbon and contains only single bonds (termed a saturated hydrocarbon. Alkanes have the general formula CH, thus, an alkane with 10 carbons (n =10)will have 2(10)+2=22 hydrogens, or the molecular formula C,Hz. The root, or parent name for an unbranched alkane is taken directly from the number of carbons in the chain according to a scheme of nomenclature established by the International Union of Pure and Applied Chemistry(IUPAC), as shown Condensed Structure methane CHa CHCH propan CH: CH2CH3 pentane CH3(CH2)3CH: CH3(CH2).CH3 CH3(CH2):: octane CH3 (CH2)CH3 CH3(CH2)CH cane CH3 (CH2)3CH3 undecane CH3 (CH])9CH; decane CH(CH2)CH Hydrocarbons, however, are not restricted to linear, unbranched chains and there are often many possible orders in which a hydrocarbon with a given molecular formula can be constructed. Compounds having the same molecular
Alkane Nomenclature Alkanes represent the simplest of the functional groups which are common in organic chemistry. An alkane contains only carbon and hydrogen (a hydrocarbon) and contains only single bonds (termed a saturated hydrocarbon. Alkanes have the general formula CnH2n+2, thus, an alkane with 10 carbons (n = 10) will have 2(10) + 2 = 22 hydrogens, or the molecular formula C1 0H2 2. The root, or parent name for an unbranched alkane is taken directly from the number of carbons in the chain according to a scheme of nomenclature established by the International Union of Pure and Applied Chemistry (IUPAC), as shown below: Name Condensed Structure methane CH4 ethane CH3CH3 propane CH3CH2CH3 butane CH3(CH2)2CH3 pentane CH3(CH2)3CH3 hexane CH3(CH2)4CH3 heptane CH3(CH2)5CH3 octane CH3(CH2)6CH3 nonane CH3(CH2)7CH3 decane CH3(CH2)8CH3 undecane CH3(CH2)9CH3 dodecane CH3(CH2)10CH3 Hydrocarbons, however, are not restricted to linear, unbranched chains and there are often many possible orders in which a hydrocarbon with a given molecular formula can be constructed. Compounds having the same molecular
formula. which differ in the order of attachment of the individual atoms are called constitutional isomers. An example of the three possible constitutional isomers of pentane (CH) are shown below. 人 Although there are only three constitutional isomers for pentane, for alkanes having larger numbers of carbons, the number of isomers is staggering: for C,he there are over 4 billion possible constitutional isomers In order to be able to communicate chemical information it is essential to have a systematic set of rule defining nomenclature for organic compounds. As mentioned previously, the IUPAC system of nomenclature accomplishes this and the rules for naming linear and branched alkanes are given below The IUPAC name for an alkane is constructed of two parts: 1)a prefix (meth.. eth... prop.. etc )which indicates the number of carbons in the main, or parent, chain of the molecule, and 2) the suffix .. ane to For branched-chain alkanes, the name of the parent hydrocarbon is taken from the longest continuous chain of carbon atom Groups attached to the parent chain are called subs titue nts and are named based on the num ber of carbons in the longest chain of that substituent, and are numbered using the number of the carbon atom on the parent chain to which they are attached. In simple alkanes, substituents are called alkyl groups and are named using the prefix for the number of carbons in their main chan and the suffix.yl. For example, methyl, ethyl, propyl, dodecyl,etc CH3 -CH2 -CH-CH3 CH3 -CH2 -CH-CH2CH If the same substituent occurs more than once in a molecule, the num ber of each carbon of the parent
formula, which differ in the order of attachment of the individual atoms, are called constitutional isomers. An example of the three possible constitutional isomers of pentane (C5H1 2) are shown below. Although there are only three constitutional isomers for pentane, for alkanes having larger numbers of carbons, the number of isomers is staggering; for C30H6 2, there are over 4 billion possible constitutional isomers. In order to be able to communicate chemical information, it is essential to have a systematic set of rule defining nomenclature for organic compounds. As mentioned previously, the IUPAC system of nomenclature accomplishes this and the rules for naming linear and branched alkanes are given below: • The IUPAC name for an alkane is constructed of two parts: 1) a prefix (meth... eth... prop..., etc.) which indicates the number of carbons in the main, or parent, chain of the molecule, and 2) the suffix ...ane to indicate that the molecule is an alkane. • For branched-chain alkanes, the name of the parent hydrocarbon is taken from the longest continuous chain of carbon atoms. • Groups attached to the parent chain are called substituents and are named based on the number of carbons in the longest chain of that substituent, and are numbered using the number of the carbon atom on the parent chain to which they are attached. In simple alkanes, substituents are called alkyl groups and are named using the prefix for the number of carbons in their main chain and the suffix ...yl. For example, methyl, ethyl, propyl, dodecyl, etc. • If the same substituent occurs more than once in a molecule, the number of each carbon of the parent