Connectivity locants

The main chain thus defined is then numbered according to the principles already specified for unbranched systems. Side chains which in turn can bear side chains of their own are treated analogously. If connecting the partial structures offers a choice, lowest possible locants are given to linking positions. If, in the case of multiple side chains, all the above priority criteria are exhausted, alphabetical order comes into play. This also holds for the citation order of side chains, irrespective of their connectivity locants. 

If a spiro system is composed of two identical subunits the connectivity locants followed by the term spirobL. are placed in front of the name of the partial system. 

These compounds are generally named glycosyl[glycosyl]n glycoses with the connectivity locants placed in round brackets between the individual component terms. The same format is used for the specific short formulae customary in carbohydrate chemistry. For disaccarides of that type Chem. Abstr. still uses the traditional 0-locants in front of the full name. 

No locants are needed m the absence of substituents it is understood that the double bond connects C 1 and C 2 Substituted cycloalkenes are numbered beginning with the double bond proceeding through it and continuing m sequence around the ring The direction is chosen so as to give the lower of two possible numbers to the substituent... 

When the parent molecules connected by the azo group are different, azo is placed between the complete names of the parent molecules, substituted or unsubstituted. Locants are placed between the affix azo and the names of the molecules to which each refers. Preference is given to the more complex parent molecule for citation as the first component, e.g., 2-aminonaphthalene-l-azo-(4 -chloro-2 -methy Ibenzene). 

When the parent molecules connected by the azo group are different, azo is placed between the complete names of the parent molecules, substituted or unsubstituted. Locants... 

In Figure 21, attention is directed to a molecule for which identical modules are bound to non-overlapping halves of a ring. Cahn and Dermer [45], name this compound trans-p-(l-4-r 5-8-r -cyclo-octatetraene)- bis-(tricarbonyliron). Godwin [46], on the other hand, recognizes that there is the possibility for connections to only some of the atoms and thus elects to include all relevant locant numbers namely p-(l,2,3,4-r - 5,6,7,8-T -cycloocta-l,3,5,7-tetraene)- bis-(tricarbonyliron). In the nomenclature being developed in this... 

Observe that in (47), the sub-cycle being nomenclated started at locant 3 and progressed through locant 20. Additionally, the connection between the sub-cycles is by means of an unprimed - primed bridge (5-17 for this cluster). 

Up until this point all examples of symmetry and repetition have concentrated on an atom being the focal center however, when dealing with spherical nomenclature, the rules can be extended so that the focus is on a bond instead. For example, biphenyl (Figure 40) is symmetric about the connecting bond consequently, instead of the above Cartesian name (76), which required the specification of additional locant numbers, one might assign as the spherical name ... 

The monomer — inside a set of parentheses or brackets (written with the highest priority atom designated as locant 2. Locant 1 is the bond connecting the monomer to the end group)... 

The principle of giving the lowest locants to the simplest or what is considered the most important modifications has often been applied to trivial names. Whenever the starting point is unambiguous as in toluene, phenol, or benzoic acid, where the ring atom connected with the modification is numbered 1, the success is satisfactory. However, the confusion possible with trivial names containing several substituents is familiar from the cresols and toluidines. There is no reason why an agreement between these numbering principles should not be reached. 

Where ring atoms have a connectivity different from their standard bonding number (see Section IR-6.2.1), their actual bonding number is expressed as an arabic superscript to the Greek letter lambda following immediately after an appropriate locant. 

This compound could certainly be named as a trisubstituted benzene ring. However, it is much more efficient to name the parent as phenol rather than benzene and to hst the two bromine atoms as substituents. The choice to name this compound as a phenol dictates that the carbon atom connected to the OH group must receive the lowest locant (number 1). When a choice exists, place numbers so that the second substituent receives the lower possible number. 

In this example, the parent is a hexane chain and the suffix is -amine. The methyl and ethyl groups are listed as substituents using the locant "N" to identify that they are connected to the nitrogen atom. 

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