Naphthalene reactivity numbers

Scheme 2. Calculation of the reactivity number (localization energy) for the 1-position of naphthalene according to the PMO and PMO-F method. (The denominator follows from the normalization condition, i.e. the normalized NBMO coefficients are inversely proportional to the root of the sum of squares of the unnormalized coefficients)...

There are principally two different approaches of correlating experimental rate data of electrophilic substitution with reactivity indices (1) Correlating the index with the rate data of a given reaction, e.g. bromination. For example, a satisfying correlation of Dewar reactivity numbers with the log of rate constants of the bromination of benzene, naphthalene (1- and 2-position), biphenyl (4-position), phenanthrene (9-position), and anthracene (9-position) has been observed [55]. In correlations of this type the reactivity index corresponds to the reactivity constant in the Hammett equation while the slope of the linear correlation corresponds to the reaction constant (see also Sect. 3) (2) correlating the index with experimental a values. 

FIGURE 5.33. Distributions of formal charge in transition states for electrophilic substitution in naphthalene and anthracene and corresponding reactivity numbers. 

First we have to predict the point of primary proton attack [equation (7.100)]. This can be done very simply by the PMO method. The product of the reaction is a radical derived from the parent hydrocarbon (here naphthalene) by addition of a hydrogen atom. The ease of proton attack on CioHg should therefore parallel that of hydrogen atom attack on naphthalene, i.e., that of a typical radical substitution (see p. 330). Attack should therefore take place at the point with the lowest reactivity number, i.e., at an a position,... 

Dewar and his co-workers, as mentioned above, investigated the reactivities of a number of polycyclic aromatic compounds because such compounds could provide data especially suitable for comparison with theoretical predictions ( 7.2.3). This work was extended to include some compounds related to biphenyl. The results were obtained by successively compounding pairs of results from competitive nitrations to obtain a scale of reactivities relative to that of benzene. Because the compounds studied were very reactive, the concentrations of nitric acid used were relatively small, being o-i8 mol 1 in the comparison of benzene with naphthalene, 5 x io mol 1 when naphthalene and anthanthrene were compared, and 3 x io mol 1 in the experiments with diphenylamine and carbazole. The observed partial rate factors are collected in table 5.3. Use of the competitive method in these experiments makes them of little value as sources of information about the mechanisms of the substitutions which occurred this shortcoming is important because in the experiments fuming nitric acid was used, rather than nitric acid free of nitrous acid, and with the most reactive compounds this leads to a... 

All azo dyes contain one or more azo groups (-N=N-) as chromophore in the molecule on the basis of the number of azo groups in each molecule, they are named monoazo-, disazo-, trisazo-, etc. The azo groups are in general bound to a benzene or naphthalene ring, but they can also be attached to heterocyclic aromatic molecules or to enolizable aliphatic groups. On the basis of the characteristics of the processes in which they are applied, the molecule of the dye is modified to reach the best performances so they can be acid dyes, direct dyes, reactive dyes, disperse dyes, or others. 

Here again the high reactivity is due to the gain of aromatic stabilization in the adduct. Polycyclic aromatics are moderately reactive as the diene component in Diels-Alder reactions. Anthracene forms adducts with a number of dienophiles. The addition occurs at the centre ring. The naphthalene ring system is much less reactive. 

A very reactive nitrogen atom is required to convert benzenes or naphthalenes into pyridines, and there are a number of such reactions which involve nitrenes or nitrenoid species. A number of substituted benzenes have been treated with sulfonyl diazide or carbonyl diazide and moderate yields of pyridines recorded (27CB1717). Thus p-xylene gives 2,5-dimethylpyridine there is no indication of the fate of the carbon atom which is lost. More controlled reaction is possible in intramolecular insertions. The examples in which o-nitrotoluene is converted into a derivative (759) of 2-acetylpyridine, and where 2,3-diazidonaphthalenes give 3-cyanoisoquinolines (760) are quoted in a review (81 AHC(28)231>. 

As in naphthalene, a fused benzene ring induces bond fixation. Hence, whereas substituents in the 1-position of isoquinoline (571 note numbering) behave like substituents in the 2-position of the pyridine nucleus, substituents in the 3-position of isoquinoline show reactivity less than that of true a-substituents and about midway between those of 2- and 3-substituents on pyridine (90AHC(47)390). 

The reactivity, site of attack, and stereochemistry of the reactions of a variety of nucleophiles (oxygen, sulfur, nitrogen, organometallic) with anti-and syn-naphthalene 1,2 3,4-dioxides have been studied recently.159 In most cases, di- or tetrasubstituted tetrahydronaphthalene products arising from attack at C-l and C-4 positions in the anti mode are produced. These isomeric diepoxides are excellent intermediates for the preparation of a number of difficulty accessible 1,4-disubstituted naphthalene derivatives. 

Equation (39) therefore remains unchanged since the term in a cancels. An exactly similar argument holds for nucleophilic substitution we therefore conclude that (1) the relative reactivities of different hydrocarbons, and the relative reactivities of different positions in the same hydrocarbon, should be the same for substitution by reagents of all kinds, and (2) there should be in each case a linear relation between log k and The first relationship holds qualitatively in all cases except where steric effects are involved thus naphthalene is more reactive than benzene to reagents of all three types (e.g. nitric acid, phenyl radicals, sodamide), and in each case the a-position in naphthalene is more reactive than the / the corresponding free valence numbers are ... 

A review of solvent properties of, and organic reactivity in, ionic liquids demonstrates the relatively small number of quantitative studies of electrophilic aromatic substitution in these media.3 Studies mentioned in the review indicate conventional polar mechanisms. 1-Methylpyrrole reacts with acyl chlorides in the ionic liquid 1-butylpyridinium tetrafluoroborate to form the corresponding 2-acylpyrrole in the presence of a catalytic amount of ytterbium(III) trifluoromethanesulfonate.4 The ionic liquid-catalyst system is recyclable. Chloroindate(III) ionic liquids5 are catalytic media for the acylation, using acid chlorides and anhydrides, of naphthalene, benzene, and various substituted benzenes at 80-120 °C. Again the ionic liquid is recyclable. 

For the hydrocarbons so far considered, which consist of benzene rings connected linearly, the number of Kekul structures is one more than the number of rings. Thus in benzene it is two, naphthalene three, anthracene four, naphthacene five and dibenzanthracene six. The number of structures with elongated tt bonds, however, increases considerably as the number of benzene rings in the molecule is increased and it is this fact that is responsible for the gradual increase in reactivity with the size of the molecule. 

The styryl radical anion species is much more reactive than the naphthalene radical anion, and rapidly couples to form a dimeric dianion, the source of the red color and the reason for the disappearance of the ESR signal (Eq. 22.40). The dimeric dianion is a double-ended anionic propagating species useful for the initiation of a number of valuable homopolymerizations (Eq. 22.41). 

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