Naming compounds cycloalkanes

The procedure used to name a cycloalkane by the IUPAC method is very similar to that used for alkanes. Here, the root designates the number of carbons in the ring and the prefix cyclo- is attached to indicate that the compound contains a ring. The rules for numbering the ring carbons are as follows ... 

The basic lUPAC system of nomenclature is straightforward the compounds are named as cycloalkane polyols, with a slash separating substituents on each side of the ring thus, 1,2,3/4,5 cyclopentane pentol has three adjacent hydroxyls on one side of the ring, and two on the other (there are four cyclopentane pentols, all achiral). 

Name compounds that have a —COOH group bonded to a cycloalkane ring as derivatives of the cycloalkane with the suffix carboxylic acid. The ring atom to which the carboxyl group is attached is C-1. Do not include this number in the name. 

We can use the nomenclature rules on page 1211 to name a cycloalkane having substituent groups. For example, we would name the following compound 1,1,3-trimethylcyclopentane not 1,3,3-trimethylcyclopentane ... 

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

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 ... 

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 . 

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. 

When the number of carbons in the ring is greater than or equal to the number of carbons in the longest chain, the compound is named as a cycloalkane. However, if an alkyl chain of the cycloalkane has a greater number of carbons, then the alkyl chain is used as the parent, and the cycloalkane as a cycloalkyl substituent. 

SAMPLE SOLUTION (a) The molecule has a tert-butyl group bonded to a nine-membered cycloalkane. It is tert-butylcyclononane. Alternatively, the tert-butyl group could be named systematically as a 1,1-dimethylethyl group, and the compound would then be named (1,1-dimethylethyl)cyclononane. (Parentheses are used when necessary to avoid ambiguity. In this case the parentheses alert the reader that the locants 1,1 refer to substituents on the alkyl group and not to ring positions.) ... 

When a cycloalkane has an alkyl substituent, the compound could be called either an alkylcycloalkane or a cycloalkylalkane. The alkylcycloalkane name is the proper one ... 

You first should decide what type of compound it is. The decision usually is straightforward for hydrocarbons, which will fall in one or the other of the categories alkanes, alkenes, alkynes, arenes, cycloalkanes, and so on. But when the compound has more than one functional group it is not always obvious which is the parent function. For example, Compound 1 could be named as an alkene (because of the double-bond function) or as an alcohol (because of the OH function) ... 

Although Hantzsch-Widman system works satisfactorily (if you can remember the rules) for monocyclic compounds, it is cumbersome for polycyclic compounds. In the case of oxiranes it is simplest for conversational purposes to name them as oxides of the cycloalkenes or epoxy derivatives of the corresponding cycloalkanes. The oxabicycloalkane names seem preferable for indexing purposes, particularly because the word oxide is used in many other connections. 

When several substituents are present on a benzene ring, the ring is numbered in the same manner as the rings of cycloalkanes—that is, so that the numbers for the substituents are as low as possible. In addition, some special terms are used with disuhsti-tuted benzenes only. Two substituents on adjacent carbons (positions I and 2) are said to be ortho, or o-. Two substituents on positions 1 and 3 are meta, or m-. And two substituents on positions 1 and 4 are para, or p-. Finally, if an alkyl group with six or more carbons is attached to a benzene ring, the compound is named as an alkane with a phenyl substituent. Some examples are as follows ... 

A second period of macrocyclic chemistry was signaled by the isolation of the first macrolide antibiotic from an Actomyces culture in 1950. Brockmann and Henkel [6][7] named it picromycin (Pikromycin) (1/4), because of its bitter taste. This antibiotic contains a 14-membered ring. Since then a large number of macrocyclic lactones, lactams and cycloalkane derivatives have been discovered. Some of these compounds have a considerable physiological importance for humans and animals. Because of these physiological properties it was necessary to prepare larger quantities of these macrocylic compounds by chemical syntheses [8]. 

Step 1 Name the parent cycloalkane. In (a), the parent is cyclohexane. If the compound has an alkyl substituent with more carbons than the ring size, the compound is named as a cycloalkyl-substituted alkane. 

The term pseudorotation was first appUed to cyclopentane like inversion, it has an atomic analogue in 5-coordinate compounds (e.g. PF5). ) The name means false rotation , and it is therefore appropriate for any conformational process which results in a conformation superposable on the original, and which differs from the original in being apparenUy rotated about one or more axes. Pseudorotation, in analogy with real molecular and internal rotations, can be free, as in cyclopentane, or more or less hindered, eis in cycloheptane and higher cycloalkanes. In moderately to severely hindered pseudorotation, it is appropriate to consider distinct stable conformations which are pseudorotation partners, and these cases are often amenable to study by dynamic nmr methods. When the barrier to pseudorotation is very low, or in the limit when pseudorotation is free, it is not really justified to talk about separate stable conformations (e.g. the C2 and Cg forms of cyclopentane), because strictly there is only one conformation, and the pseudorotation is simply a molecular vibration. 

In the past several years organic chemists have attempted to synthesize some unusual cycloalkanes not found in nature. Dodecahedrane, a beautifully symmetrical compound composed of 12 five-meinbered rings, is one such molecule. It was first prepared at Ohio State University in 1982. The lUPAC name for dodecahedrane is undecacyclo[9.9.9.0 .a - .(f V 0. 0 0 ° ". 0 .0 ]eicosane, a name so complex that few trained organic chemists would be able to identify its structure. 

We thus have the families cycloalkanes, cycloalkenes, and cycloalkynes, as well as the multi-double and triple-bond variants such as cycloalkadienes and -atrienes, and cycloalkadiynes, -atriynes, etc. Naming the cyclo compounds corresponds to the naming of the straight-chain forms except that carbon atoms are numbered such that substituents are on the lowest numbered carbon atoms. This... 

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