Naming cycloalkanes

To name a cycloalkane, name and locate each substituent on the ring and prefix the name of the analogous open-chain alkane with cyclo-. 

When one substituent is attached to a carbon atom in a cycloalkane, the name of the substituent is placed in front of the cycloalkane name. No number is needed for a single alkyl group or halogen atom because the carbon atoms in the cycloalkane are equivalent. 

As you can see cycloalkanes are named under the lUPAC system by adding the prefix cyclo to the name of the unbranched alkane with the same number of carbons as the ring Substituent groups are identified m fhe usual way Their posifions are specified by numbering fhe carbon atoms of fhe ring m fhe direction fhaf gives fhe lowesf num ber to fhe subsfifuenfs af fhe firsf pomf of difference... 

A single alkane may have several different names a name may be a common name or it may be a systematic name developed by a well defined set of rules The most widely used system is lUPAC nomencla ture Table 2 6 summarizes the rules for alkanes and cycloalkanes Table 2 7 gives the rules for naming alkyl groups... 

Count the number of carbons in the ring and assign a basis name to the cycloalkane corre spending to the lUPAC name of the unbranched cycloalkane having the same number of carbons... 

Name the alkyl group and append it as a prefix to the cycloalkane No locant is needed if the com pound IS a monosubstituted cycloalkane It is understood that the alkyl group is attached to C 1... 

Cycloalkenes and their derivatives are named by adapting cycloalkane termmol ogy to the principles of alkene nomenclature... 

Para (Section 11 7) Term describing a 1 4 relationship be tween substituents on a benzene nng Paraffin hydrocarbons (Section 2 18) An old name for al kanes and cycloalkanes... 

The name naphthenic acid is derived from the early discovery of monobasic carboxyUc acids in petroleum, with these acids being based on a saturated single-ring stmcture. The low molecular weight naphthenic acids contain alkylated cyclopentane carboxyUc acids, with smaller amounts of cyclohexane derivatives occurring. The carboxyl group is usually attached to a side chain rather than direcdy attached to the cycloalkane. The simplest naphthenic acid is cyclopentane acetic acid [1123-00-8] (1, n = 1). 

Paraffin hydrocarbons (Section 2.18) An old name for alkanes and cycloalkanes. 

Alicyclic Hydrocarbons. These refer to cyclic analogues of aliphatic hydrocarbons and are named accordingly, using the piefix cyclo-." Their properties are similar to their open-chain aliphatic counterparts. Alicyclic hydrocarbons are subdivided into monocyclic (cycloalkanes, cycloalkenes, cycloalkynes, cycloalkadienes, etc.) and polycyclic aliphatic compounds. Monocyclic aliphatic structures having more than 30 carbon atoms in the ring are known, but those containing 5 or 6 carbon atoms are more commonly found in nature [47, p. 28]. 

Substituted cycloalkanes are named by rules similar to those we saw in the previous chapter for open-chain alkanes (Section 3.4). For most compounds, there are only two steps. 

Count the number of carbon atoms in the ring and the number in the largest substituent chain, (f the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane. If the number of carbon atoms in the largest substituent is greater than the number in the ring, the compound is named as a cycloalkyl-substituted alkane. For example ... 

Interactive to learn to write lUPAC names for simple cycloalkanes. 

Interactive to use an online palette to draw cycloalkane structures from their lUPAC names. 

As with cycloalkanes (Section 4.1), benzenes with more than two substituents are named by choosing a point of attachment as carbon 1 and numbering the substituents on the ring so that the second substituent has as low a number as possible. If ambiguity still exists, number so that the third or fourth substituent has as low a number as possible, until a point of difference is found. The substituents are listed alphabetically when writing the name. 

To name an alkane in which the carbon atoms form a single chain, we combine a prefix denoting the number of carbon atoms with the suffix -ane (Table 18.1). For example, CH,—CH, (more simply, CH,CH,) is ethane and CH,—CH2—CH, (that is, CH,CH2CH,) is propane. Cyclopropane, C,H6 (15), and cyclohexane, C6H12 (16), are cycloalkanes, alkanes that contain rings of carbon atoms. 

EXAMPLE 18.1 Sample exercise Naming alkanes and cycloalkanes... 

Write the structural formulas for and name (a) at least 10 alkene isomers having the formula C(1HI2 (b) at least 10 cycloalkane isomers have the formula CftH12. 

The reductive cyclization of enynes has been used to prepare exo-methylene-cycloalkanes. Two systems have proven successful in this transformation, namely PMHS/Pd2(dba)3 CHCl3245 (Eq. 102) and Et3SiH/Pd(dppe)Cl2/HC02H (Eq. 103).246... 

This compound can be neither an alkane or a cycloalkane. Its name is ethene, with a double bond. This could be the formula for a cycloalkane, since its formula matches C H2 . 

It is of course possible to name individual radialenes according to IUPAC rules [e.g. per(methylene)cycloalkanes 1-4]. However, the descriptiveness of the term radialene may some day pave its way into the official nomenclature. For substituted [ ]radialenes we have proposed1 a pragmatic numbering system, in which an inner ring is numbered first, followed by an outer ring . The numbering of substituents should follow IUPAC rules. Thus, the hydrocarbon 7 is 4,4-diethyl-5,5-dimethyl[3]radialene, the ester 8 should be called 7-methoxycarbonyl-5,5-dimethyl[4]radialene, the nitrile 9 which can exist in four diastereomeric forms is (6Z,7Z)-6-cyano-5,5,7-trimethyl[4]radialene and the difunctionalized [5]radialene 10 is (7 ,6Z)-7-bromo-6-formyl-6-methyl[5]radialene. 

The enthalpy of fomation of two such species has been measured, namely the cyclopropane and cycloheptane derivatives. The difference between the values for these two species, both as solids, is 238.1 kJmol . Is this difference plausible Consider the difference between the enthalpies of formation of the parent cycloalkanes as solids, 194 kJ mol . The ca 44 kJ mol discrepancy between these two differences seems rather large. However, there are idiosyncracies associated with the enthalpies of formation of compounds with three-membered rings and almost nothing is known at all about the thermochemistry of compounds with seven-membered rings. Rather, we merely note that a seemingly well-defined synthesis of cycloheptyl methyl ketone was shown later to result in a mixture of methyl methylcyclohexyl ketones, and superelectrophilic carbonylation of cycloheptane resulted in the same products as methylcyclohexane, namely esters of 1-methylcyclohexanecarboxylic acid. The difference between the enthalpies of formation of the unsubstituted alicyclic hydrocarbons cycloheptane and methylcyclohexane as solids is 33 kJmol . This alternative structural assignment hereby corrects for most of the above 44 kJ mol discrepancy in the enthalpies of formation of the two oximes. More thermochemical measurements are needed, of oximes and cycloheptanes alike. 

Cyclic ethers can be named simply as oxacycloalkanes, such as oxacyclopropane, oxacyclo-butane, oxacyclopentane, and oxacyclohexane, where the prefix oxa indicates the replacement of CH2 by O in corresponding cycloalkanes. Most cyclic ethers, however, are known by other names. The 3-, 4-, 5-, and 6-membered rings are oxirane, oxetane, oxolane, and oxane, respectively, or ethylene oxide (or epoxide), trimethylene oxide, tetrahydrofuran, and tetrahydropyran. 

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