Bipolar compound

In principle, dimeric molecules may also be made out of different halves leading to asymmetric compounds. Different substituted arylamines have been coupled by Thompson et al. [66]. Tme bipolar compounds with a different electronic character in each half will be discussed in Section VI in the context of their redox properties. Despite their polar character, the tendency toward crystallization can be low, and amorphous films are obtained. 

Bipolar Molecular Glasses. Recently, bipolar molecular glasses have been described that allow both injection of holes and electrons (Fig. 3.30). 2- 4-[bis(4-methylphenyl)amino]phenyl -5-(dimesitylboryl)thiophene (PhAMB-lT, 68) and 2- 4-[bis(9,9-dimethylfluorenyl)amino]phenyl -5-(dimesitylboryl)thiophene (F1AMB-1T, 69) show oxidation potentials of 0.62 and 0.58 V, and reduction potentials of —2.13 and —2.01 V vs. Ag/0.01 Ag+, respectively [145]. Oxidation as well as reduction leads to stable radical ions. With the conversion rules given above, the HOMO and LUMO levels can be estimated to be approximately at —5.3 and —2.8 eV. In comparison, for the bipolar compound 70, consisting of triarylamine and oxadiazole moieties, the values are —5.5 and — 2.7eV [129]. However, in this case no data on the stability of the radical ions are available. 

Give at least three examples of environmentally relevant classes of (a) apolar, (b) monopolar, and (c) bipolar compounds. In the case of the monopolar compounds, indicate whether they are electron donors (H-acceptors) or electron acceptors (H-donors). 

Fig. 3.4 shows that when plotting the air-pure liquid compound partition constants of a large number of chemicals versus their dispersive vdW parameters, the apolar and monopolar compounds fall more or less on one line, while the bipolar compounds do not show this behavior. Explain these findings. For which kind of bulk liquids (give examples) would you expect that in a similar plot, all compounds (including the bipolar ones) should fit one line ... 

In general, we see that the enthalpic contribution is larger than the entropic one, but also that these contributions co-vary. This is true for a very diverse group of compounds at a given temperature (25°C), including apolar, monopolar, and bipolar compounds. Hence, if we view the forces between the molecules (the glue ) to be reflected primarily in the enthalpy term, then p h is a direct measure of these forces in the pure liquid. 

Figure 4.7 Plot of Avaptf,- versus In p L for a large number of apolar, monopolar, and bipolar compounds. Note that some bipolar outliers are not included. (For details see Goss and Schwarzen-bach, 1999a.)...

Furthermore, for most compounds of interest to us, the octanol molecules present as cosolutes in the aqueous phase will have only a minor effect on the other organic compounds activity coefficients. Also, the activity coefficients of a series of apolar, monopolar, and bipolar compounds in wet versus dry octanol shows that, in most cases, Yu values changes by less than a factor of 2 to 3 when water is present in wet octanol (Dallas and Carr, 1992 Sherman et al., 1996 Komp and McLachlan, 1997a). Hence, as a first approximation, for nonpolar solvents, for w-octanol, and possibly for other solvents exhibiting polar groups, we may use Eq. 6-11 as a first approximation to estimate air- dry organic solvent partition constants for organic compounds as illustrated in Fig. 6.2. Conversely, experimental KM data may be used to estimate K,aw or Kitvi, if one or the other of these two constants is known. 

Figure 6.5 Plot of the decadic logarithms of the air-cyclohexane versus the air-hexadecane partition constants of a series of apolar, monopolar, and bipolar compounds. Data from Abraham et al. (1994b).

Figure 6.7 Plot of the decadic logarithms of the air-olive oil partition coefficients versus the air-octanol partition constants for various sets of structurally related apolar, monopolar, and bipolar compounds. Note that olive oil is a mixture of compounds that may vary in composition. Therefore, we refer to A" a oUve oi] as the air-olive oil partition coefficient (and not constant, see Box 3.2). Adapted from Goss and Schwarzenbach (2001). The a and b values for the LFERs (Eq. 6-12) are alkanes (a - 1.15, b = 0.16), alkyl aromatic compounds (a = 1.08, b = 0.22), ethers (a = 0.97, 6 = 0.01), esters (a = 0.88, b = -0,14), ketones (a = 1.21, b = 1.06), alcohols (a = 0.98, b = 1.07).

In a series of papers on the mechanism of the Friedel-Crafts reaction, Korshak and co-workers attributed the catalytic activity of aluminum chloride to the formation of bipolar compounds and have presented evidence in favor of their mechanism which involves reactions of aro-... 

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