Branched hydrocarbons, naming

A whole lubricating oil fraction consists of four major classes of hydrocarbons—namely (a) asphalts and resins, (b) aromatics, (c) naphthenes and branched paraffins, and (d) paraffin wax. Sulfuric acid is remarkably effective for removing undesirable constituents a and b by a combination of reaction and extraction and has little or no effect on wax (which must be removed by other means) or the naphthenic-type materials which comprise a good lubricating oil. 

When every carbon atom in a hydrocarbon except the two terminal ones is bonded to only two other carbon atoms, the molecule is called a straight-chain hydrocarbon. (Do not take this name literally, for, as the w-pentane structures in Figure 12.1 show, this is a straight-chain hydrocarbon despite the zigzag nature of the drawings representing it.) When at least one carbon atom in a hydrocarbon is bonded to either three or four carbon atoms, the molecule is a branched hydrocarbon. Both wo-pentane and /w-pentane are branched hydrocarbons. 

To discern how many carbon atoms are in a straight chain or branch of a carbon compound, prefixes are used. If all the carbon-carbon bonds are single bonds, the hydrocarbon name ends in -ane. These molecules are called alkanes. If there is a double carbon-carbon bond, the name ends vn-ene. These molecules are called alkenes. If there is a triple carbon-carbon bond, the name ends in -yne. These molecules are called alkynes. 

The best way to learn to name branched hydrocarbon molecules is to apply the rules to an example molecule ... 

The correct numbering shows us that the branch comes from the third carbon atom in the straight chain. Therefore, the hydrocarbon name begins with the number 3. There is one carbon atom in the branch, so the branch name begins with meth- and ends in -y/—methyl. The straight chain has six carbon atoms (hex-) with only single bonds (-ane), so it is named hexane. Put it all together and we have 3-methylhexane. 

When a hydrocarbon has more than one branch, the branches are named as indicated above, beginning with the branch of smallest number. For example ... 

This hydrocarbon is named 3-methyl 5-ethyloctane. In this octane molecule, if both branches were methyl branches, the name would be 3,5 dimethyl octane. 

The names of the alkanes beyond butane are obtained by adding the suffix -arte to the Greek root for the number of carbon atoms (pent- for five, hex- for six, and so on). For a branched hydrocarbon, the longest continuous chain of carbon atoms determines the root name for the hydrocarbon. For example, in the alkane... 

Name branched hydrocarbons from their structural formulas. 

The steps to follow for naming organic compounds with functional groups are similar to those for naming branched hydrocarbons. 

Name the following branched hydrocarbon. (Hint The —CH2—CH3 group is an ethyl group.)... 

For a branched hydrocarbon, the longest continuous chain of carbon atoms gives the root name for the hydrocarbon. For example, in the alkane... 

To what does the root name for a branched hydrocarbon correspond ... 

This is a branched hydrocarbon. The name is based on the longest carbon chain. The name is... 

This is also a branched hydrocarbon. The longest chain includes the C2H5 group the name is based on hexane, not pentane. This is an old trick. Carbon chains are flexible and don t have to lie in a straight line. The name is 2,3,4-trimethylhexane. Why not 3,4,5-trimethylhexane ... 

An isomer of butane, for example, has the same molecular formula as the straight-chained compound shown in Figure 14-2, C4H10, but a different bonding pattern. This isomer is mostly referred to by the common name isobutane and is what I call a branched hydrocarbon. Check out Figure 14-3 to see it shown in a variety of ways. 

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