Nomenclature parent chain

Based on everything we learned in the second chapter (nomenclature), w>e would name this compound 3,4-dimethylhexan-2-one. Now w e must also add the configurations to the name. The stereocenter on the left is R, and the stereocenter on the right is S. We use the numbering system of the parent chain to determine where the... 

Reaction of an a-substituted enolate with an aldehyde or ketone can give two pairs of aldol dia-stereomers, which are conveniently designated as the syn form (17) and the anti form (18), where is part of the parent chain in lUPAC nomenclature (equation 29). For simplicity, only one enantiomer of each pair will usually be shown throughout this section. The syn/anti notation for aldol diastereomers has been described in detail by Heathcock. ... 

In the I.U.P.A.C. Nomenclature System, the parent chain is the longest continuous carbon chain to which the amino group is bonded. The name of the parent alkane is used as the suffix and is preceded by the word amino and a number that designates the position of the amino group on the chain. A few examples follow ... 

To illustrate how these names were obtained, consider structure (c). The longest continuous chain that contains the double bond is made up of 4 carbons. Therefore, the parent chain is butene, the "ene" indicative of the presence of a double bond. The double bond is situated on carbon so that it is 1-butene. The two substituents, both methyl groups (CH3), are positioned on carbon 3 because the numbering system is from the end of the parent chain nearest the double bond. Hence, for (c) the nomenclature is 3,3-Dimethyl-l-butene. 

Once candidate parent chains have been identified, the algorithm ranks the selected candidate structural units (ring(s) and functional parent(s), if any, have already been identified in the previous phases) according to the relevant nomenclature principles. If more than one candidate structural unit of the same rank competes for selection as a parent, the following sequence of principles, in the order given, is applied until a decision is reached ... 

General. Continuous-chain alkanes are the sole parent hydrides for all compounds, the skeleton of which is composed of chains. Cyclic parent hydrides are more diverse. In nomenclature, they are classified according to their structure as carbo-cycles (composed of carbon atoms only) and heterocycles (composed of carbon atoms and other atoms, such as N, O and Si). They are also classified as saturated and unsaturated. Saturated cycles have the maximum number of hydrogen atoms attached to every skeletal atom, as judged by a prespecified valence unsaturated cycles have fewer hydrogen atoms and multiple bonds between pairs of atoms. 

Compounds composed of rings and chains are also named using substitutive nomenclature. The ring, whether carbocyclic or heterocyclic, is always selected to be the parent hydride. 

The classical progestins as well as the corticosteroids arc based on a steroid nucleus that incorporates a two-carbon side chain at the 17 position that often includes a carbonyl group at position 21. The hypothetical parent hydrocarbon has been assigned the name pregnane for purposes of nomenclature. While two classes of compounds, progestins and corticoids, share common biosynthetic pathways, their biological activities differ markedly. 

In general, organic compounds are given systematic names by using the order prefix-parent-suffix, where prefix indicates how many branching groups are present, parent indicates how many carbons are in the longest chain and suffix indicates the name of the family. Common names as weU as systematic names are used for alkanes and their derivatives. However, it is advisable to use systematic names or the lUPAC (International Union of Pure and Applied Chemistry) nomenclature, which can be derived from a simple set of rules. 

IUPAC nomenclature names ethers as alkoxy alkanes, alkoxy alkenes, or alkoxy alkynes. The group in the chain that has the greatest number of carbon atoms is designated the parent compound. In the case of aromatic ethers, the benzene ring is the parent compound. 

The IUPAC rules for naming aldehydes append the suffix -al to the parent name. The aldehyde carbon is always the first carbon in the chain, so a locant is not necessary. The simplest aldehyde, methanal, is commonly known as formaldehyde, a highly toxic gas used to preserve biological specimens. Ethanal is the next aldehyde, although most organic chemists call it acetaldehyde. 2,2,2-Tri-chloroethanal, more commonly known as chloral, reacts with water to form the sedative chloral hydrate. Phenylmethanal, more commonly known as benzalde-hyde, is used as artificial cherry or almond flavoring. Nomenclature examples of aldehydes are shown in Figure 11.34. 

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