Alkanes naming substituents

The longest continuous chain that contains the —CH group provides the base name for aldehydes. The -e ending of the corresponding alkane name is replaced by -al, and substituents are specified in the usual way. It is not necessary to specify the location of O... 

In Method 2, described by Rule A-31, the saturated cyclic parent is named as a polycyclo-[.. jalkane. The alkane name identifies the total number of carbon atoms in the ring system. The names bicyclo, tricyclo, tetracyclo, etc. identify parent compounds of two, three, four, etc. rings. Double bonds in the ring are identified by names such as w-alkenc, ,/w-alkadicne, where the n and m give the position of the double bond. Substituents consist of alkyl, cycloalkyl, phenyl, etc. radicals. 

Most organic compounds can be derived from alkanes. In addition, many important parts of organic molecules contain one or more alkane groups, minus a hydrogen atom, bonded as substituents onto the basic organic molecule. As a consequence of these factors, the names of many organic compounds are based on alkanes. It is useful to know the names of some of the more common alkanes and substituent groups derived from them, as shown in Table 1.3. 

In addition to the locations of the double bonds, another difference of alkenes is the molecule s inability to rotate at the double bond. With alkanes, when substituent groups attach to a carbon, the molecule can rotate around the C-C bonds in response to electron-electron repulsions. Because the double bond in the alkene is composed of both sigma and pi bonds, the molecule can t rotate around the double bond (see Chapter 6). What this means for alkenes is that the molecule can have different structural orientations around the double bond. These different orientations allow a new kind of isomerism, known as geometrical isomerism. When the non-hydrogen parts of the molecule are on the same side of the molecule, the term cis- is placed in front of the name. When the non-hydrogen parts are placed on opposite sides of the molecule, the term trans- is placed in front of the name. In the previous section, you saw that the alkane butane has only two isomers. Because of geometrical isomerism, butene has four isomers, shown in Figure 19.12. 

Name substituent groups as in alkanes, indicating their locations by the number of the main-chain carbon to which they are attached. The ethenyl group and the propenyl group are usually called the vinyl group and the allyl group, respectively. 

Systematic names for aldehydes are derived by replacing the final -e of the alkane name with -al. An aldehyde carbon is at the end of a chain, so it is number 1. If the aldehyde group is a substituent of a large unit (usually a ring), the suffix carbaldehyde is used. 

The IUPAC nomenclature for amines is similar to that for alcohols. The longest continuous chain of carbon atoms determines the root name. The -e ending in the alkane name is changed to -amine, and a number shows the position of the amino group along the chain. Other substituents on the carbon chain are given numbers, and the prefix N- is used for each substituent on nitrogen. 

IUPAC Names of Dicarboxylic Acids Aliphatic dicarboxylic acids are named simply by adding the suffix -dioic acid to the name of the parent alkane. For straight-chain dicarboxylic acids, the parent alkane name is determined by using the longest continuous chain that contains both carboxyl groups. The chain is numbered beginning with the carboxyl carbon atom that is closer to the substituents, and these numbers are used to give the positions of the substituents. 

The location and name of each substituent are followed by the root alkane name. The substituents are listed in alphabetical order, and the prefixes di-, tri-, and so on, are used to indicate multiple, identical substituents. 

Each alkane-based substituent group branching from the parent chain is named for the straight-chain alkane having the same number of carbon atoms as the substituent. The ending -ane is replaced with the letters -yl, as shown in the following diagram. 

Common alkyl groups—replace "ane" ending of alkane name with "yl". Alternate names for complex substituents are given in brackets. 

In the lUPAC system, alkyl halides are named as substituted alkanes. The substituent prefix names for the halogens end with o (i.e., fluoro, chloro, bromo, iodo ). Therefore, alkyl halides are often called haloalkanes. 

To arrive at the systematic name of a diene, we first identify the longest continuous chain that contains both double bonds by its alkane name and then replace the ne ending with diene. The chain is numbered in the direction that gives the double bonds the lowest possible numbers. The numbers indicating the locations of the double bonds are cited either before the name of the parent compound or before the suffix. Substituents are cited in alphabetical order. Propadiene, the smallest member of the class of compounds known as allenes, is frequently called allene. 

The lUPAC nomenclature for carboxylic acids uses the name of the alkane that corresponds to the longest continuous chain of carbon atoms. Tlie final -e in the alkane name is replaced by the suffix -oic acid. The chain is numbered, starting with the carboxyl carbon atom, to give positions of substituents along the chain. In naming, the carboxyl group takes priority over any of the functional groups discussed previously. 

Rule 5 The last substituent alkyl group is used as a prefix to the parent alkane name. 

Branched chains and other groups are treated as in naming alkanes. Name the substituent group, and designate its position on the parent chain with a number. 

We form lUPAC names of alkenes by changing the -an- infix of the parent alkane to -en-(Section 3.5). Hence, CH2 = CH2 is named ethene, and CH3CH=CH2 is named propene. In higher alkenes, where isomers exist that differ in the location of the double bond, we use a numbering system. We number the longest carbon chain that contains the double bond in the direction that gives the carbon atoms of the double bond the lower set of numbers. We then use the number of the first carbon of the double bond to show its location. We name branched or substituted alkenes in a manner similar to the way we name alkanes (Section 3.3). We number the carbon atoms, locate the double bond, locate and name substituent groups, and name the main (parent) chain. 

Punctuation is important when writing fUPAC names. fUPAC names for hydrocarbons are written as one word. Numbers are separated from each other by commas and are separated from letters by hyphens. There is no space between the last named substituent and the name of the parent alkane that follows it. 

The molecule marked 12A is a seven-carbon straight-chain alkane named heptane. However, 12A is color coded in a peculiar manner such that a methyl group is attached to the end of a six-carbon linear chain. Can an alkyl substituent be added to the end of a linear chain Adding a methyl group in this fashion gives a seven-carbon unbranched chain, which is heptane, of course. Adding a methyl group to the end of a chain simply extends the linear chain. 

Alkane 16 poses a problem. The longest unbranched chain is 17, so it is a hepta-decane, with a methyl and an ethyl group. In terms of sequencing the substituents in the name, ethyl will come before methyl, but the nearest locant is 5 for either group. Therefore, it could be 5-ethyl-13-methylheptadecane or 13-ethyl-5-methyl-heptadecane. The rule states that if the same substituent numbers are obtained in either direction, numbering should be in the direction giving the lowest number to the first named substituent. Therefore, 20 is 5-ethyl-13-methylheptadecane. 

Although the instruction to name substituents on alkanes in alphabetical order looks simple, the process is a bit complex because some modifiers count in the alphabet and others do not. Table 2.5 contains a brief summary. 

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