Fusion prefixes

The following contracted fusion prefixes may be used furo, imidazo, isoquino, pyrido, quino and thieno. 

In a compound name for a fusion prefix when more than one pair of square brackets is required), the points of fusion in the compound prefix are indicated by the use of unprimed and primed numbers, the unprimed numbers being assigned to the ring attached directly to the base component, thus ... 

Fusion prefixes are used to designate to which side of the parent hydrocarbon a substituent nng is attached. 

Abbreviation for normal (unbranched), as in n-butane. naphtho The ring fusion prefix derived from naphthalene. 

With the exception of benzo, fusion prefixes for monocyclic systems are treated as exemplified for cyclopenta, cyclohepta etc. It should be noted here that for fused polycyclic systems the ending. ..ene always indicates the maximum number of non-cumulative double bonds, that is, a man-cude system ... 

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... 

When ring fusions and/or bridges are present in addition to spiro linkages, the fused or bridged units are first named individually (by any of the available methods) and the names are then cited (in square brackets and in alphabetical order) with the prefix spiro- or dispiro-, etc. Points of spiro attachment are indicated between the names of the components, with primes as necessary (examples 64-66). This method is also applicable to structures like (62) and (63) but is more cumbersome. 

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). 

Systematic names can he derived hy relating hack to the parent heterocycle and using the prefix henzo to indicate its fusion to benzene. It is necessary to define which of the bonds in the heterocycle is... 

When a system does not have a retained name or a name that can be composed systematically as above, and when ortho- and ortho-peri- x% on are possible, it is named using fusion nomenclature, i.e. by combining the names of the two or more systems that are fused. One system is adjudged to be the senior according to criteria described elsewhere and is taken as a parent hydride, and the other is denoted in the name by a non-detachable prefix. The junction of the two systems is indicated in a specific manner. Instead of numerical locants, italic letters a , 6 , c , etc. are used to identify bonds in the parent hydride. The final letter o and normal locants are characteristic of the prefix. The examples below illustrate the fusion operation and the resulting fusion name. 

The prefix selenopheno is used to denote selenophene fusion in this chapter, following the greater part of the literature in the field. Chemical Abstracts and the lUPAC Rules of Nomenclature prefer the (possibly confusing) form selenolo. [Editors.]... 

The systematic nomenclature for the cycloproparenes is confused because the fusion rule (IUPAC Rule A 21.3) requires that at least two rings of five or more members be present before the prefix cyclopropa may be used. Thus while l//-cyclopropa[a]- and -[/ naphthalene are correct for 10 and 11, respectively, 1 //-cyclopropabenzene is incorrect for 1. The Chemical Abstracts service and IUPAC are unanimous in naming 1 as bicyclo-[4.1. Ojhepta-1,3,5-triene la. Thus if the parent member is strictly named, not only does it differ from that of its higher homologues, but also it could be taken to imply a bond localized structure. Throughout this chapter parent 1 and its derivatives 5-9 are referred to as cyclopropabenzenes and numbered as shown for structure 1. 

A component fused to the base component (referred to as a primary component) is cited as a prefix terminating usually in o, with the locants of the bond engaged in fusion specified in square brackets in the order corresponding to the direction of lettering of the base component, as in example 13. A (secondary) component fused to a primary component is cited as a further prefix, with the use of primes to indicate the... 

Two methods are available for naming bridged cyclic skeletons. One (the von Baeyer system see the following section, 5) is particularly suitable for naming predominantly saturated skeletons the other, to be described now, is appropriate for predominantly unsaturated skeletons and involves citing the bridge as a prefix to a fusion name. 

In fusion names, the a terms precede the complete name of the parent hydrocarbon. Prefixes denoting ordinary substitution precede the a terms. 

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