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Alkyl benzenes electron density

Fig. 64. Plausible model of the molecular packing of the cast multibilayer of 34 as produced by electron-density matching of the X-ray diffraction data. The plane of the benzene ring is arbitrarily set in the plane of the two alkyl chains. When the benzene plane is assumed to be in the perpendicular disposition, the tilt angles for the spacer and tail chains become slightly greater 50° for the spacer and 75° for the tail [445]... Fig. 64. Plausible model of the molecular packing of the cast multibilayer of 34 as produced by electron-density matching of the X-ray diffraction data. The plane of the benzene ring is arbitrarily set in the plane of the two alkyl chains. When the benzene plane is assumed to be in the perpendicular disposition, the tilt angles for the spacer and tail chains become slightly greater 50° for the spacer and 75° for the tail [445]...
Borazine is isoelectronic with benzene, as B=N is with C=C, (Fig. 16.21). in physical properties, borazine is indeed a close analogue of benzene. The similarity of the physical properties of the alkyl-substituted derivatives of benzene and borazine is ever more remarkable. For example, the ratio of the absolute boiling points of the substituted borazines to those of similarly substituted benzene is constant. This similarity in physical properties led to a labeling of borazine as "inorganic benzene." This is a misnomer because tbe chemical properties of borazine and benzene are quite different Both compounds have aromatic rr clouds of electron density with potential for delocalization over all of the ring atoms. Due to the difference m electronegativity between boron and nitrogen, the cloud in borazine is "lumpy" because more electron... [Pg.918]

A linear correlation between 13C chemical shifts and local n electron densities has been reported for monocyclic (4n + 2) n electron systems such as benzene and nonbenzenoid aromatic ions [76] (Section 3.1.3, Fig. 3.2). In contrast to theoretical predictions (86.7 ppm per n electron [75]), the experimental slope is 160 ppm per it electron (Fig. 3.2), so that additional parameters such as o electron density and bond order have to be taken into account [381]. Another semiempirical approach based on perturbational MO theory predicts alkyl-induced 13C chemical shifts in aromatic hydrocarbons by means of a two-parameter equation parameters are the atom-atom polarizability nijt obtained from HMO calculations, and an empirically determined substituent constant [382]. [Pg.254]

The displacement of electrons belonging to alkyl groups towards the aromatic ring, and the consequent increase in electron density of the ring reduce the rate of exchange as compared with benzene. This is shown by the following rate constants (sec-1) for C KNDj = 0-02n at 25° ... [Pg.184]

As the table indicates C6o solubility and the amount of ortho- nitro isomers increases concurrently, i.e. with increasing 7i-electron density in the ortho-positions of alkyl derivatives of benzene. [Pg.29]

The plot is a straight line passing through the origin of the coordinates. This is evidence that C6o solubility depends linearly on the ti-electron density in the ortho-position of alkyl derivatives of benzene. [Pg.29]

The examples of C6o dissolution in benzene derivatives considered in the present work evidence the clear dependence of C6o solubility on the electron density distribution in the benzene ring. We have identified a priori the electron density with the distribution of ortho-, meta-, para-isomers which form in the reactions of electrophilic substitution of the benzene derivative considered. This identification is evaluated but in some cases, such as in a series of homologs for alkyl derivatives of benzene, the total agreement between the C6o solubility and the amount of ort/io-isomers is observed (Table 2 and Fig. 7). [Pg.34]

The rate constant for the bromination of toluene (methylbenzene) is about 4000 times that for benzene (this may sound like a lot, but the fate constant for N,N-dimethylaniline is 1014 times greater). The methyl group also directs electrophiles mostly into the ortho and para positions. These two observations together suggest that alkyl groups may also increase the electron density in the 7t system of the benzene ring, specifically in the ortho and para positions, rather like a weakened version of an OR group. [Pg.561]

Many substituted benzene rings undergo electrophilic aromatic substitution. Common substituents include halogens, OH, NH2, alkyl, and many functional groups that contain a carbonyl. Eiach substituent either increases or decreases the electron density in the benzene ring, and this affects the course of electrophilic aromatic substitution, as we will learn in Section 18.7. [Pg.653]


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See also in sourсe #XX -- [ Pg.655 ]




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