Naming the Alkanes

Branched alkanes are constitutional isomers of straight-chain alkanes 

Branched alkanes are derived from the straight-chain systems by removal of a hydrogen from a methylene (CH2) group and replacement with an alkyl group. Both branched and straight-chain alkanes have the same general formula, C H2 +2. The smallest branched alkane is 2-methylpropane. It has the same molecular formula as that of butane (C4H10) but different connectivity the two compounds therefore form a pair of constitutional isomers (Section 1-9). 

For the higher alkane homologs (n 4), more than two isomers are possible. There are three pentanes, C5H12, as shown below. There are five hexanes, CeH nine heptanes, C7H16 and eighteen octanes, CgHig. 

The number of possibilities in connecting n carbon atoms to each other and to 2n + 2 surrounding hydrogen atoms increases dramatically with the size of n (Table 2-4). 

Propane stored under pressure in liquefied form in canisters such as these is a common fuel for torches, lanterns, and outdoor cooking stoves. 

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This concludes the derivation of our bond energy formula and the presentation of simple examples pertaining to saturated systems, namely, the alkanes, including their numerical parameterization. 

Continuing in the alkane series (also called the paraffin series because the first solid hydrocarbon in the series is paraffin, or candle wax), the next compound is pentane. This name is derived from the Greek word penta, for five. As its name implies, it has five carbon atoms, and its molecular formula is C,H12. From pentane on, the Greek prefix for the numbers five, six, seven, eight, nine, ten, and so on are used to name the alkanes, the Greek prefix corresponding to the number of carbon atoms in the molecule. The first four members of the alkane series do not use the Greek... 

The names of the alkenes are formed with the same prefixes used in naming the alkanes. These prefixes correspond to the number of carbon atoms in the compound. The suffix is -ene, which indicates that the compound belongs to the alkene family. Thus the simplest member of the alkene family, C2H4, should be called ethene. Ethene is commonly known as ethylene, Figure 1-8. The next larger member of the family, propene, commonly is called propylene. 

Name the alkanes which have the following formulae ... 

To name the alkanes according to the lUPAC system the following rules can be used. 

To name an epoxide as an epoxyalkane, first name the alkane chain or ring to which the oxygen is attached, and use the prefix epoxy to name the epoxide as a substituent. Use two numbers to designate the location of the atoms to which the O s are bonded. 

A gaseous alkane is burned completely in oxygen. The volume of the carbon dioxide that forms equals twice the volume of the alkane burned (the volumes are measured at the same temperature and pressure). Name the alkane and write a balanced equation for its combustion. 

Proceeding to the next homolog, we find that thermolysis of 70 produces 5-azoxy radical 71, which leads to products typical of perester thermolysis, namely, the alkane, alkene, and... 

Name the alkane corresponding to the longest chain containing the ketone group by changing the... 

Abstraction of hydrogen by chlorine is exothermic, which, according to Hammond s postulate, means that the transition state for H absfracfion by Cl is reached early in the course of the reaction [Figure 8.3(a)]. Therefore, fhe strucfure of the transition state for this step resembles the reactants, namely the alkane and a chlorine atom, not the product radicals. As a result, there is relatively little radical character on carbon in this transition state, and regioselectively in radical chlorination is only slightly influenced by the relative stabilities of radical intermediates. Products are determined more by whether a chlorine atom happens to collide with a 1°, 2°, or 3° H. 

In the lUPAC system of naming, the longest carbon chain is numbered to give the location of one or more substituents attached to it. Let s take a look at how we use the lUPAC system to name the alkane shown in Sample Problem 17.1. 

In Summary Four rules should be applied in sequence when naming a branched alkane (1) Find the longest chain (2) And the names of aU the alkyl groups attached to the ston (3) number the chain (4) name the alkane, with substituent names in alphabetical order and preceded by numbers to indicate their locations. Haloalkanes are named in accord with the rules that apply to naming the alkanes, the halo substituent being treated the same as alkyl groups. 

We can now name the alkane, placing the substituents in alphabetical order (lUPAC rale 4). In this respect, recall that the prefix di in diethyl is not counted, because it is merely multiplying the substituent whose name is ethyl. In contrast, the di in dimethylcyclo-propyl is part of that complex substituent s name, and therefore is counted in the alphabetization. Thus, dimethylcyclopropyl comes before diethyl (alphabetized as ethyl ). The result is 5-(ci5 -2,3-dimethylcyclopropyl)-l,l-diethylcyclooctane. 

Ethyl alcohol, the common name of ethanol, also indicates attachment of the —OH group to the ethane hydrocarbon chain. To name the alkane chain as a group, replace the final -e with -yl, so that ethane becomes ethyl, thus ethyl alcohol for CH3CH2OH. It is often the case that the common name of one compound, alcohol in this case, will provide the generic name for a complete class of compounds that is, all alcohols contain at least one —OH group. 

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