Norbomane system

Another interesting example is a study on rate data in solvolysis reactions.[19]. It was found that exo substituted norbomane systems were classified to belong to the same class as substrates which were known to give rise to stabilized carbocations. 

The bridging of cyclopentane to form a norbomane system which, according to H. Brown, is also accelerating the solvolysis leads in fact to other results. An increase in angle strain upon the sp - sp transformation in both a cyclopentane and a norbomane system must be essential but nearly the same (for cyclopentanone v o = 1750 cm , for 2-norbomanone v, o = 1751 cm ). At the same time... 

Menthol (peppermint oil) is an example of a substitnted cyclohexane natural product, whereas camphor (from the camphor tree) and jS-cadinene (from jnniper and cedar) are simple bicyclic terpenes, the first a norbomane system, the second a decalin derivative. 

Recently a reverse perturbation effect of a cyclopropyl group on facial selectivities was described in two bicyclic systems, bicyclo[2.2.2]octane 59 and norbomane (bicyclo[2.2.1]heptane) 60 [124]. Bicyclo[2.2.2]octene 59a, annulated with an exo-cyclopropyl group, i.e., exo-tricyclo[3.2.2.0 ]non-6-ene, and 7-methylenenor-bomane 60a, annulated with an exo-cyclopropyl group, i.e., 8-... 

The results of dry ozonation, namely, regioselectivities and stereoselectivities, are very similar to those in superacidic liquid-phase ozonation. Tertiary C—H bonds in strained systems such as norbomane are inert to dry ozonation.93 Such compounds are oxidized at the secondary carbon to yield a mixture of alcohols and ketones.93 104 Similarly, substituted cyclopropanes exhibit a general preference for the oxidation of the secondary C—H bond in the a-position to the ring 104... 

The differences in the hybridizations of the exocyclic bridgehead bonds of adamantane and norbomane are reflected by the bridgehead C13-H coupling constants observed for the two systems Jq1 3-H = 120 lHz for all hydrogens in adamantane 1S°) Jq 3 h = 139 1 Hz for norbomane 172). These coupling constants correspond to 24 and 28 % s character for the exocyclic bridgehead C orbitals of adamantane and norbomane, respectively 173). 

Rule 1. Use the name norbomane for the fundamental saturated ring system, which is bicyclo[]2.2.1]] heptane. Use the name bornane for the saturated larger parent compound, which is 1,7,7-trimethylbicyclo[]2.2.1]] heptane. Form a series of names based on these two new terpene names. 

A bonding electron pair that is contained in a C—C single bond is normally not a neighboring group. However, one famous exception is a particular bonding electron pair in the norbomane ring system (Figure 2.25). It is fixed in precisely such a way that it can interact with a reaction center on C2. 

Tertiary G—H bonds are more reactive than secondary ones, primary G—H bonds are least reactive. For example, the relative rates for insertion (corrected for the number of hydrogens of each type) into the G—H bonds of 2-methylbutane by ethoxycarbonylnitrene are about 30 10 1 297.324 Pivaloylnitrene is somewhat more selective . Ethoxycarbonylnitrene inserts readily into bridgehead G—H bonds in small bicyclic systems, such as norbomane or tricyclo[3.3.0.0 ] octane . The insertion is stereospecific, wfith retention of configuration both in intramolecular nitrene cyclizations " and in the inter-... 

Polycyclic compounds contain two or more rings that share two or more carbon atoms. We can illustrate the naming system with norbomane whose systematic name is bicycIo[2.2.1]heptane (a) heptane since it contains a total of seven carbon atoms (b) bicyclo, since it contains two rings, that is, breaking two carbon-... 

These effects can occur when the active site at which a measurable phenomenon occurs is in close proximity to the substituent. Among the many systems exhibiting direct steric effects are orf/ic-substituted benzenes, 1, c/s-substituted ethylenes, 2, and the ortho- (1,2-, 2,1- and 2,3-) and peri- (1,8-) substituted naphthalenes, 3, 4, 5 and 6, respectively. Other examples are c/s-1,2-disubstituted cyclopropanes, c/s-2,3-disubstituted norbomanes and c/s-2,3-disubstituted [2.2.2]-bicyclooctanes, 7, 8 and 9, respectively. Some systems generally do not show steric effects. Vicinally substituted systems such as disubstituted methanes, 10, and 1,1-disubstituted ethenes, 11, are examples, 2,3-Disubstituted heteroarenes with five-membered rings such as thiophenes and selenophenes... 

A very comprehensive report on the nomenclature of terpenes has been approved by the lUPAC and the American Chemical Society (4). Some of the significant changes in nomenclature recommended are the replacement of the names camphane and bomylane by bomane. Norbomane replaces norcamphane and norbomylane. Thujane is preferred over sabinane. A definite system of numbering the bicyclo ring systems is recommended. The application of these terpene rules will eliminate many trivial names which are a tax on the memory. 

In E2, the two groups to be eliminated must be coplanar. In conformationally mobile systems like acyclic molecules, or in cyclohexanes, anti-coplanar is the preferred orientation where the H and leaving group are 180° apart. In rigid systems like norbomanes, however, SYN-coplanar (angle 0°) is the only possible orientation and E2 will occur, although at a slower rate than anti-coplanar. 

In the norbomane series, the attack of LAH in Et20 takes place on the exo face, leading to enrfo-norbomanols 3.41. These are the thermodynamically less stable products. Therefore, the reductions performed by LAH do not follow product development control, but essentially depend on stereoelectronic factors [AB2] (Figure 3.16). The same exo attack is observed in other strained bicyclic systems. In general, Lil -BuljBH in THF at —78°C is more stereoselective than LAH in THF [KG2]. 

Another common ring system is the norbomane, or bicyclo 2.2.1]hep-tane, structure. Like decalin, norbomane is a bicycloalkane, so-called because fury rings would have to be broken open to generate an acyclic structure. Its systematic name, bicyclo 2.2.1]heptane, reflects the fact that the molecule has seven carbons, is bicyclic, and has three bridges of 2,2, and 1 carbon atoms connecting the two bridgehead carbons. 

Kropp and coworkers have been concerned with systems in which homolysis is followed by rapid electron transfer, such as the photolysis of certain alkyl halides [55]. Photolysis of the norbomyl phenyl sulfoxide 110 was examined. The notion was that sulfide photolysis is usually homolytic, but the sulfinyl radical is more electronegative than the sulfenyl (thiyl) radical, which might assist in electron transfer reactions. Thus, it was thought, ionic reactivity might be observed. In addition to inversion of the sulfur center and deoxygenation (yide infra), norbomane 111 and norbomene 112, both presumed to... 

Sargent points out, however, that Goeiing s reasoning does not consider the transition from the spA to the sp -hybridized state in the norbomane and the bicyclo[2,2,2]octane systems connected with various angle strain changes. By employing Foote s correlation Sar t shows that if the angle strain effects are corrected,... 

A proposed system for the conversion and storage of solar energy was based on the photochemical isomerization of norbomadiene (3) to quadricyclane (4) during sunny periods, with catalytic conversion of 4 to 3 and release of energy at a later time. The heats of hydrogenation of 3 and 4 (both in tihe liquid phase) to norbomane are —68.0 kcal/mol and —92.0 kcal/mol, respectively. What is the potential for energy storage, in kcal/mol, for the photochemical conversion of 3 to 4 ... 

Further support for the nonclassical structure of the 2-norbomyl cation came from an application of NMR spectroscopy that is based on the difference between the total chemical shift of a carbocation and that of the corresponding alkane. Differences in total chemical shift of 350 ppm or more are associated with classical carbocations, while differences of less than 200 ppm are thought to indicate nonclassical, bridged carbonium ions. For example, the sum of the total NMR chemical shift of propane is 47 ppm, while the sum for the 2-propyl cation is 423 ppm. The difference, 376 ppm, indicates that the 2-propyl cation is a classical ion. For the 2-norbomyl system the total of the shifts is 408 ppm, while the total for norbomane is 233 ppm. The difference, 175 ppm, was taken as evidence for a nonclassical structure. ... 

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