Prefixes dehydro

In one method, the non-detachable prefixes hydro- and dehydro- (in the case of mancudes only) can be used to indicate the addition or subtraction of one hydrogen atom. As even numbers of hydrogen atoms are involved when a carbon-carbon single bond becomes a double or triple bond, the multiplicative prefixes di-, tetra-, etc., as well as the appropriate locants, are used. The prefix dehydro- is always used to indicate the subtraction of hydrogen atoms from saturated heterocycles having Hantzsch-Widman names. 

A further complication exists in the case of certain alkaloids where the parent name is given to the tetrahydro base and the related quaternary alkaloid, although often naturally occurring, is named by asing the prefix dehydro-. ... 

In addition to the usual suffixes and prefixes just discussed, a few special prefixes are usually used for the semi-trivial names of the compounds. Thus the prefix dehydro- is used to indicate the loss of two hydrogen atoms from adjacent carbon atoms with the formation of a double bond (e.g, dehydroepiandrosterone). The prefix dihydro- or tetrahydro- indicates the addition of two or four hydrogen atoms to the molecule, respectively, as in dihydrocortisol and tetrahydrocortisol. The replacement of a hydroxyl group by hydrogen (COH CH) is denoted by the prefix deoxy- (or desoxy- [e.g., 11-deoxycorticosterone]). 

Individual compound names are derived from parent names in the usual way by specifying the degree of hydrogenation (with -ene, -yne, hydro- and dehydro-) e.g. 84 and 85) and the substituents (with appropriate prefixes and suffixes). However, there are other ways in which parent names can be modified. Changes in stereochemistry can be indicated by use of the prefix ent- (meaning a reversal in configuration of all asymmetric centres) or by... 

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). 

Note. The treatment of anhydro (see 2-Carb-26), dehydro (see 2-Carb-17.3) and deoxy as detachable prefixes follows long-standing practice in carbohydrate chemistry, but is in conflict with [14] (p. 12). 

Alternatively they can be named on the basis of the corresponding fully saturated sugar by using the appropriate number of dehydro and deoxy prefixes (deoxy operations are regarded as formally preceding dehydro operations). The prefixes are placed in alphabetical order before the stem name. 

Note Hydro and dehydro prefixes, if treated as detachable (see Rule C-16.11), are considered along with prefixes for substituents when this criterion is applied. 

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