Phenanthrenes double

In the case of pyrene, there are two sextets and two fixed double bonds similar to the phenanthrenic double bond. In agreement with this argument and with the result for phenanthrene, co-ozonolysis of pyrene with formaldehyde or acetyl cyanide afforded the expected normal ozonide 114 and the cross-ozonide 115 with an aldehydic group. In a separate co-ozonolysis of 115 with vinyl acetate, diozonides 116 were prepared. No cross-ozonide was obtained in the presence of benzoyl cyanide, which afforded only the normal mono-ozonide 114 (Scheme 36 and Table 15). 

The substruetures A - D aeeount for eleven of the total of twelve double bond equivalents so that the eompound eontains one additional ring as present in anthraeene or phenanthrene skeletons. 

For phenanthrene the five unexcited structures lead to V double bond character for the 9-10 bonds, Y forthe l-2bonds, 2/sforthe 1-11,11-12 and 4-12 bonds, and l/ for the 10-11 and 12-13 bonds, and the predicted configuration is... 

The acid 19 has been dimerized, although in low yield, in the course of a perhydro-phenanthrene synthesis [141]. When the oxidation potential of the double bond is sufficiently lowered by alkyl substituents, lactone formation by oxidation of the couble bond rather than of the carboxyl group occurs (Eq. 7) [142] (see also chap. 15). 

Bonds in the "K-region" are usually short (1.34-1.35 A), near in values to that for a pure double bond, while most other C-C bonds in PAHs are in the range 1.36-1.44 A. The second area of interest is the "bay region" (27) which corresponds to the hindered region between the 4- and 5- positions of phenanthrene (the area between CIO and Cll of BP (I) or Cl and C12 of DMBA (II), for example). 

The only reported 1,2-addition providing a relatively stable adduct is that of a 1,2-cycloaddition of phthalazinedione to indene (Scheme 40). Compound 162 was isolated and characterized (66JOC3862 71CC695). A similar 1,2-addition reaction to the 9,10-double bond of phenanthrene was also reported but not firmly documented (66JOC3862). 

The partially hydrogenated phenanthrene derivative 18 (entry 4) is a very moderate diene due to the steric crowding caused by the substituents and the anulated rings, and it reacts even with highly reactive dienophiles such as maleic anhydride (MA) or N-phenylmaleic imide only at high pressure. The minor product 20 in the reaction with MA obviously stems from diene 21. This can be explained by a double-bond isomerization 18 - 21 prior to the cycloaddition, certainly catalyzed by traces of acid present in the MA. In the absence of acid only the Diels-Alder adduct 22 derived from diene 18 was observed. In the reaction of diene 23 with MA (entry 5) a similar sequence of steps was observed. A [1,5] shift of the C—O bond in 23, again certainly acid-catalyzed, produces the diene 26 followed by the Diels-Alder reaction with MA to give 24 and 25. 

One of the interesting molecules that has been studied in considerable detail is nor-bomadiene (80). Much of this interest has been associated with the interactions between the double bonds of the system. Thus irradiation affords quadricyclane (81). This area of study will be discussed later in this chapter. The radical cation 82 can also be formed from both norbomadiene and quadricyclane by irradiation in acetonitrile/methanol solution with the DCB/phenanthrene sensitizer system. Several products (Scheme 2) are formed in low yield and it should be noted that there is little difference in the yields of products obtained from either starting material. However, it is evident that attack by methanol occurs from the exo face32. 

The l,3,5-triene-l,3-cyclohexadiene interconversion is a six-electron electrocycli-zation that requires a cis central double bond to occur.245 An important application of this rearrangement is the photocyclization of cis-stilbene to dihydrophenanthrene [Eq. (4.45)], which is usually further oxidized to phenanthrene 249... 

The 1,2 bonds in both napthalene and anthracene are in fact shorter than the other ring bonds, whereas the 9,10 bond in phenanthrene closely resembles an alkene double bond in both its length and chemical reactivity. 

Exercise 22-31 Draw the Kekule-type valence-bond structures for napthalene, anthracene, and phenanthrene. Estimate the percentage of double-bond character for the 9,10 bond of phenanthrene, assuming that each of the valence-bond structures contributes equally to the hybrid structure. 

However, the 9,10 bond in phenanthrene is quite reactive in fact it is almost as reactive as an alkene double bond. Addition therefore occurs fairly readily ... 

The double-bond character of the 9,10 bond in phenanthrene is particularly evident in ozonization. This bond is attacked preferentially, which leads to the formation of a dialdehyde when the ozonide is reduced with iodide ion ... 

Recently, several studies have been made of the photolysis of disilanes or polysilanes in the presence of an electron-deficient alkene using a photosensitizer (such as phenanthrene) and acetonitrile as solvent. These conditions result in the addition of silyl groups to one end of the alkene double bond and hydrogen to the other end (equation 18) and evidently involve the reaction of the radical anions of the electron-deficient silene with silyl radicals67 (see also Section VIII.A). 

For phenanthrene hydrate the derived value of p fR is —11.6. This is comparable to values for the benzhydryl (-12.5) or / -methylphenethyl (-12.8) cations.22,69,73 The evaluation of p fR as well as pKa allows derivation of p h2o = pA"R — pKa = 9.3. This equilibrium constant offers a measure of the stability of the 9,10-double bond of phenanthrene and thus the aromaticity of its central benzene ring. Comparison with the double bond of 2-butene, for which p h2o = —3.94,86 indicates a 1013-fold greater stability, for the aromatic double bond. It should be noted that the value of p h2o does not depend on azide trapping. In the difference between p fR and pKA the rate constant kAz cancels out and K o = kAkn2o/knkp. 

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