Locant designators

Nomenclature system . The prefix 17 indicates that all unsaturated carbon atoms of the ligand indicated are ir-bonded to the metal atom for complexes in which the metal atom is bonded only to particular carbon atom(s) of a ligand, the total (x) of such metal-bonded atoms is indicated by a superscript (tj ) or, for ambiguous cases, by preceding locant designators, e.g. (tj -allyl), (1-4-Tj-cyclooctatetraene). 

As in xanthene above because of the symmetry, the hydrogen atom can be depicted exclusively at locant 1, rather than "floating" between the two nitrogen atoms. In other words, there is no need for an ambiguous locant designator a — as shall be the case for some of the molecules to be described in Chapter 9. 

Fig. 22 Calix-3-arene with cartesian locant designations...

The addendum to the Tresent Status summary discussed the matter of locant designators (Rule 11), the coordination of ligands in less than their maximum functionality (Rule 13), abbreviations (Rule 16), and the coordination of tautomeric forms of a ligand. 

The prefixes /ac- and mer- (facial and meridianal) are accepted. Letters are to be used as locant designators around a center of coordination. Their use has been extended to (1) multidentate ligands (even branched ones), (2) all known configurations around a central atom, and (3) multinuclear entities (provided they are not branched). 

Figure 16 Alkaloids of Prosopis juliflora juliprosopine (807) juliprosine (808) 3""-oxo-juliprosopine (809) 3-oxojuliprosine (810) 3 -oxojuliprosine (811) prosoflorine (812). The locant designations 3, 3, and 8"" in structures 809-811 are in accordance with the numbering system used in Ref. 467.

Notice that because they define the ends of the carbon chain in 2 phenylbutanedial the aldehyde positions are not designated by numerical locants in the name... 

The systematic lUPAC name of ethyl acetoacetate is ethyl 3 oxobutanoate The presence of a ketone carbonyl group is indicated by the designation oxo along with the appro priate locant Thus there are four carbon atoms m the acyl group of ethyl 3 oxobutanoate C 3 being the carbonyl carbon of the ketone function... 

Locant (Section 2 12) In lUPAC nomenclature a prefix that designates the atom that is associated with a particular structural unit The locant is most often a number and the structural unit is usually an attached substituent as in... 

Lactones, l xictides, iMciams, and Lactims. When the hydroxy acid from which water may be considered to have been eliminated has a trivial name, the lactone is designated by substituting -olactone for -ic acid. Locants for a carbonyl group are numbered as low as possible, even before that of a hydroxyl group. 

For monosubstituted alkylphenols, the position of the alkyl radical relative to the hydroxyl function is designated either with a numerical locant or ortho, meta, or para. The alkyl side chain typically retains a trivial name. Thus 4-(l,l,3,3-tetramethylbutyl)phenol, 4-/ f2 octylphenol, and para-tert-octy Tph.eno (PTOP) all refer to stmcture (1). 

Dialkylphenols employ locants to designate the position of the alkyl groups on the ring. Thus, 2,6-bis(l,l-dimethylethyl)phenol, 2,6-di-/ f2 -butylphenol, and 2,6-DTBP each refer to stmcture (2). 

Systematic names of the Hantzsch-Widman type, as well as fusion names, imply unsaturation to the extent of the maximum number of noncumulative double bonds. Suitable suffixes (Table 3) serve to identify the fully saturated derivatives. Partially unsaturated rings may be designated by hydro prefixes with locants and an even-numbered multiplier, such as 2,3-dihydro , applied to a fully unsaturated name, or by dehydro prefixes applied to the saturated name, e.g. (116). 

Most heterocyclic anions may be considered to be derived by loss of a proton from a parent compound, which is therefore the conjugate acid. Such anions have at least one unshared pair of electrons at the anionic site. They are named by appending the suffix -ide , with elision of a terminal e (lUPAC recommendation RC-83.1.1), as in (190)-(193). The site may be specified by a locant placed immediately before the suffix, and so chosen as to be as low as possible consistent with the numbering of the skeleton of the parent compound. The locant may be omitted in order to designate an equilibrating mixture of positionally isomeric anions, which is what one usually obtains in practice. The anion of piperidine is often informally referred to as piperidide . 

If a cyclic form is to be named, the locants of the anomeric centre and of the carbon atom bearing the ring oxygen atom must be given (in that order) (cf. 2-Carb-6.4). If there is more than one ring size designator, they are placed in alphabetical order (e.g. furanose before pyranose). 

Rules for designating isotopic substitution and labelling are given in [13] (Section H). Parentheses indicate substitution square brackets indicate labelling. The locant U indicates uniform labelling. 

There are two established methods in use for citing locants either in parentheses between the glycosyl and glycose terms, or in front of the glycosyl prefix, as in the names of glycosides. The former (preferred) method is derived from that used to designate residues in oligosaccharides (see 2-Carb-37 and -38). 

Oligosaccharide and polysaccharide structures occur not only in free form but often as parts of glycopeptides or glycoproteins [11] or of glycolipids [21]. It can be cumbersome to designate their structures by using the recommendations of 2-Carb-37. The use of three-letter symbols for monosaccharide residues is therefore recommended. With appropriate locants and anomeric descriptors, long sequences can thus be adequately described in abbreviated form. 

D. Where there is no conflict with other guidelines, triple bonds are senior to double bonds, which in turn are senior to single bonds multiple bonds should be assigned the lowest possible locants. Thus, the polymer from 1,3-butanediene polymerized in the 1,4- mode is usually indicated as-(—C—C=C—C — )-but is named as though it were-( - C=C - C - C - )-and named poly(l-butene-1,4-diyl) with the appropriate cis- or tra i-designation. Polyisoprene, typically drawn as-(—CH2 —C(CH3)=CH—CH2 —) —is frequently named poly(2-methyl-1,3-butadiene) but is named as though its structure were-(C(CH3)=CH—CH2—CH2 — ) —with the namepoly(l-methyl-1 -butene-1,4-diyl). 

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