Hydro prefixes

The lowest-numbered locant for substituents named as prefixes, hydro prefixes, -ene, and -yne, all considered together in one series in ascending numerical order... 

As described in Section 1.02.2.3, any heterocycle can be named by indicating (with appropriate prefixes) the positions of heteroatoms in the corresponding carbocycle. The carbocycle can be named systematically, as described in later Sections however, the replacement procedure can also be applied to naming heterocyclic analogues of trivially named carbocycles. A list of polycarbocycles with their trivial names is given in Table 5 (taken from Rule A-21.2 in the lUPAC Blue Book (B-79MI10200)) replacement names may be derived as shown in examples (27) and (28). As demonstrated by example (28), it is unnecessary to add hydro prefixes if the heterocycle cannot accommodate as many double bonds as the original carbocycle. 

The two most commonly applied systems for naming polycyclic parents are in some ways complementary. Fusion nomenclature provides names for structures containing the maximum number of non-cumulative double bonds von Baeyer nomenclature (Section 1.02.3.4) names fully saturated structures. Thus names for partially hydrogenated structures can be arrived at either by adding hydro prefixes to fusion names or ene , diene , etc. suffixes to von Baeyer names (see examples 29 and 30). If needed, rules are available for... 

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). 

Radicals from partially hydrogenated heterocycles may be named in two ways in the usual manner, using the appropriate hydro prefix for the parent compound, or by use of the indicated hydrogen convention (italic capital H and locant, enclosed in parentheses). The symbol for the indicated hydrogen must be written immediately following the locant for the radical site, e.g. (163). 

In substitutive nomenclature the use of the prefix oxo- or the suffix -one means the insertion of =0 in place of two hydrogen atoms. This is straightforward when the parent carries a CHz group at the appropriate position (example 206), but often the insertion of =0 requires prior reduction of a double bond. When the prefix oxo- is employed, this is achieved by using the appropriate hydro- prefix terms (example 207). However, the suffix -one can be used without hydro , the required reduction being implied rather than overtly stated (example 208) if desired the position of the hydrogen atom introduced to accommodate the carbonyl can be indicated in parentheses (see also examples 123 and 124). 

Thus in many cases Stelzner replacement names require hydro- prefixes where the heterocyclic skeleton is in fact maximally unsaturated. This is a notable disadvantage, which often causes confusion, and the method is not recommended. 

The Hantzsch-Widman system provides names for both fully saturated and fully unsaturated molecules. Partially saturated molecules are named by attaching appropriate hydro prefixes to the names of the fully saturated rings however the special suffixes applicable to four-and five-membered rings may also be used (this is not now recommended... 

When the two conditions of paragraph (a) are not fulfilled, positions in the skeleton of the corresponding hydrocarbon that are occupied by hetero atoms are denoted by a prefixes, and the parent heterocyclic compound is considered to be that which contains the maximum number of conjugated or isolated double bonds, but the corresponding hydrocarbon is named in the form in which it contains the maximum number of non-cumulative double bonds. Hydrogen additional to that present in the parent heterocyclic compound is named by hydro prefixes and/or as H in front of the a terms. 

If the corresponding carbocyclic system is partially or completely hydrogenated, the additional hydrogen is cited using the appropriate H- or hydro- prefixes. A trivial name from Tables 1.5 and 1.6, if available, along with the state of hydrogenation may be used. In the specialist nomenclature for heterocyclic systems, the prefix or prefixes from... 

Nomenclature follows IUPAC recommendations (79PAC2251). The basic macrocyclic system I is named porphyrin, which implies that the pyrrolic nitrogen atoms are placed in positions-21 and -23, regardless of the structure of the actual tautomer. Hydro prefixes are then considered in ascending numerical order. I attempt here to maintain the arrangements of the formulas of hydroporphyrins resulting from these rules. 

For anions ending in -ide, use a hydro- prefix and an -ic acid ending. For example, what is the chemical name for HCl and HCN ... 

Hydro-. Prefix meaning (a) an acid containing no oxygen, or (d) a compound containing hydrogen, as in the word hydrocarbon. 

A few metalloid derivatives are named according to the parent heterocycle, e.g., (VII), M = 2, are metalloindanes and (VII), = 3, are metallochroman derivatives or metallonaphthalene derivatives (hydro prefixes are required to denote saturation). Thus, compounds of structural type (VIII) are metal derivatives of isoindane or isochroman. 

Saturation at the heteroatom is indicated by H (in the above example, SH) and saturated carbons by hydro prefixes. As in the systems described in previous sections, common names are often used, particularly for heteroatom derivatives of dihydroanthracene. The nomenclature is briefly discussed for each of the systems in the following sections. 

Some substituents are always cited as prefixes, most notably halogen atoms. Otherwise, the highest-ranking substituent (the principal characteristic group) is cited as a suffix and the rest of the substituents as prefixes. Except for hydro , prefixes are cited in alphabetical order before the name of the parent hydride, parentheses being used to avoid ambiguity. 

An acid can be described as a substance that yields hydrogen ions (W ) when dissolved in water. Formulas for acids contain one or more hydrogen atoms as well as an anionic group. Anions whose names end in -ide form acids with a hydro- prefix and an -ic ending, as shown in Table 2.5. In some cases two different names seem to be assigned to the same chemical formula. 

Acids consisting of hydrogen and one other element are named for the element with a hydro- prefix and an ending of -ic. These acids include HF, hydrofluoric HCl, hydrochloric acid HBr, hydrobromic acid and HjS, hydrosulfuric acid. Another acid named in this manner is HCN, hydrocyanic acid. 

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