Branched chains, of carbon atoms

Alkanes (saturated straight or branched chains of carbon atoms)... 

Acyclic alkanes have the molecular formula C H2 +2 (where = an integer) and contain only linear and branched chains of carbon atoms. They are also called saturated hydrocarbons because they have the maximum number of hydrogen atoms per carbon. 

Two isomers, such as isobutane and n-butane, have the same atoms in their molecules, but the atoms are arranged differently. We have seen on the preceding page that in n-butane the four carbon atoms are bonded together to form a zigzag chain. In isobutane there is a branched chain of carbon atoms, as shown in the adjacent drawing. 

Of the fat-soluble pigments, carotenoids have been best characterized. They are unsaturated hydrocarbons with branched chains of carbon atoms containing a cyclic structure at one or both ends. For the chemical structures of carotenoids, see Florey (1966). 

Alkanes—Among saturated hydrocarbons, also known as alkanes, those based on a straight- or branched-chains of carbon atoms have the formula C H2 +2-Alkanes that differ in sequence by a constant unit form a homologous series. Hydrocarbons can adopt different conformations, or arrangements, of their atoms. Alkanes... 

Data for the specific rate coefficients for abstraction from CH bonds have been derived from experiments with hydrocarbons with different distributions of primary, secondary, and tertiary CH bonds. A primary CH bond is one on a carbon that is only connected to one other carbon, that is, the end carbon in a chain or a branch of a chain of carbon atoms. A secondary CH bond is one on a carbon atom connected to two others, and a tertiary CH bond is on a carbon atom that is... 

Alkanes (also called normal paraffins or n-paraffins). These constituents are characterized by branched or unbranched chains of carbon atoms with attached hydrogen atoms, and contain no carbon-carbon double bonds (they are saturated). Examples of alkanes are pentane (C5H12) and heptane (C7H16). 

Alkenes (also called olefins). These constituents are characterized by the presence of branched or unbranched chains of carbon atoms. Alkenes are not generally found in crude oil but are common in refined products, such as naphtha (a precursor to gasoline). Common gaseous alkenes include ethylene (CH2=CH2) and propene (also called propylene, CH3CH=CH2). 

A large variety of hydrocarbons have been identified in marine sediments and petrolemn. These chains of carbon atoms vary greatly in munber and some are branched, as illustrated in Figure 22.8. Some have double or triple bonds. Hydrocarbons with double or triple bonds are said to be unsaturated with respect to hydrogen. 

In large organic, or carbon-based, compounds, there are often long chains of carbon atoms, which can be straight-chain or branched. Hydrogen and oxygen are the atoms that are most commonly attached to the carbons, but the atoms of various other elements are often included. 

Number the carbon atoms within the longest chain of carbon atoms for the structure in exercise 51. How many branches extend off of this chain ... 

Curiously a whole branch of chemistry is centered on a single element. The main reason is the strength of the carbon-to-carbon bonds. Long chains of carbon atoms, one bonded to another, are possible. 

When we studied organic molecules in Chapter 5, we realized that chains of carbon atoms with branches appear in a variety of shapes. Cyclic molecules were possible. Catalysts worked to change the rate of a chemical reaction because one molecule fit into another, like puzzle pieces. Catalysts worked because of the molecular shapes of the interacting molecules. Clearly, molecules have distinct shapes. 

Table 11.1 lists the normal alkanes. Normal alkanes have a linear chain of carbon atoms with no branching. Notice that the stem names for the C5-C10 alkanes are the Latin equivalent of the number pent = 5 hex = 6, etc. 

Over 100 fatty acids are known to occur naturally. They vary in chain length and degree of unsaturation. Nearly all have an even number of carbon atoms. Most consist of linear chains of carbon atoms, but a few have branched chains. Fatty acids occur in very low quantities in the free state and are found mostly in an esterified state as components of other lipids. The pKa of the carboxylic acid group is about 5, and under physiological conditions, this group will exist in an ionized state called an acylate ion e.g., the ion of palmitic acid is palmitate, CH3(CH2)i4COO". 

These previous examples of hydrocarbons show chains of carbon atoms and branches on the chains. There are also classes of hydrocarbons that are arranged in rings. For example, a molecule of cyclopropane can be represented as shown in Figure 11.3. 

The names of alkanes with radical branches use the name from Table 18-2 for the longest continuous chain of carbon atoms. The radicals are named using the -yl ending presented in Table 18-3, and their positions along the carbon chain are denoted by a number. For example,... 

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... 

The positions of substituent groups are specified by numbering the longest chain of carbon atoms sequentially, starting at the end closest to the branching. For example, the compound... 

While the chain of carbon atoms may become more or less branched it always remains an open chain. Examples of straight and branched chains may be given by two of the isomeric pentanes. 

Naming branched-chain alkenes When naming branched-chain alkenes, follow the lUPAC rules for naming branched-chain alkanes—with two differences. First, in alkenes the parent chain is always the longest chain that contains the double bond, whether it is the longest chain of carbon atoms or not. Second, the position of the double bond, not the branches, determines how the chain is numbered. Note that there are two 4-carbon chains in the molecule shown below, but only the one with the double bond is used as a basis for naming. This branched-chain alkene is 2-methylbutene. 

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