Toluene, dipole moment

Some examples will illustrate the application of the theory to particular molecules. In toluene, the observed direction of the dipole moment shows that electrons have baen transferred from the methyl group to the ring. Hence substitution takes place readily, particularly at the o- and -positions, which have the greatest excess of electrons. 

A resolution into two or more components always occurs if the solvent has a high proton affinity, so that a solvent molecule can form a particularly stable association with a phenol molecule as a result of an energetically favourable mutual orientation. This is the case, for example, if benzene and toluene are used as the solvents. However, this effect is even more pronounced in the case of cyclohexene. Dielectric constant measurements for phenol in various solvents agree with this observation. In particular, the dipole moments in benzene and cyclohexene (1-45 and 1-79 D respectively), are considerably greater than the value of 1-32 in cyclohexane. Liittke and Mecke (1949) attributed this effect to the ability of this unsaturated solvent to act as a proton acceptor, i.e. to form 7r-complexes. 

When mixed SAMs of NMB and DMAMB were prepared in toluene, the surface NO2 concentration, as determined by external reflection FTIR spectroscopy, displays a plateau at about 40%. If one assumes that the equilibrium concentration of the two components in the mixed SAM, in a nonpolar solvent, is driven by the formation of a two-dimensional assembly with zero net dipole moment, the results can be explained by using the Hammett equation. 

Fig. 9.11 a) Chemical structures of MMB and TFMB. b) Possibilities to reduce the total dipole moment in a SAM of mercaptobiphenyls by interactions with a polar solvent, tilt or assembly of opposite dipoles in mixed monolayers, c) Surface versus solution composition found for MMB and TFMB mixed systems in polar (ethanol) and less polar (toluene) solutions illustrating the effect of the assembling dipoles, d) The opposite molecular dipoles of MMB and TFMB proved to be sufficient to induce ligand exchange in order to reach an equilibrium situation in the surface composition (modified from ref [96]). 

The dipole moment is a fundamental property of a molecule (or any dipole unit) in which two opposite charges are separated by a distance . This entity is commonly measured in debye units (symbolized by D), equal to 3.33564 X 10 coulomb-meters, in SI units). Since the net dipole moment of a molecule is equal to the vectorial sum of the individual bond moments, the dipole moment provides valuable information on the structure and electrical properties of that molecule. The dipole moment can be determined by use of the Debye equation for total polarization. Examples of dipole moments (in the gas phase) are water (1.854 D), ammonia (1.471 D), nitromethane (3.46 D), imidazole (3.8 D), toluene (0.375 D), and pyrimidine (2.334 D). Even symmetrical molecules will have a small, but measurable dipole moment, due to centrifugal distortion effects. Methane " for example, has a value of about 5.4 X 10 D. 

Water freezes to ice at 0°C expands by about 10% on freezing boils at 100°C vapor pressure at 0°, 20°, 50°, and 100°C are 4.6, 17.5, 92.5, and 760 torr, respectively dielectric constant 80.2 at 20°C and 76.6 at 30°C dipole moment in benzene at 25°C 1.76 critical temperature 373.99°C critical pressure 217.8 atm critical density 0.322 g/cm viscosity 0.01002 poise at 20°C surface tension 73 dynes/cm at 20°C dissolves ionic substances miscible with mineral acids, alkalies low molecular weight alcohols, aldehydes and ketones forms an azeotrope with several solvents immiscible with nonpolar solvents such as carbon tetrachloride, hexane, chloroform, benzene, toluene, and carbon disulfide. 

The dipole moment is a property of the molecule that results from charge separations like those discussed above. However, it is not possible to measure the dipole moment of an individual bond within a molecule we can measure only the total moment of the molecule, which is the vectorial sum of the individual bond moments.32 These individual moments are roughly the same from molecule to molecule,33 but this constancy is by no means universal. Thus, from the dipole moments of toluene and nitrobenzene (Figure 1.10)34 we should expect the moment of p-nitrotoluene to be about 4.36 D. The actual value 4.39 D is reasonable. However, the moment of p-cresol (1.57 D) is quite far from the predicted value of 1.11 D. In some cases, molecules may have substantial individual bond moments but no total moments at all because the individual moments are canceled out by the overall symmetry of the molecule. Some examples are CC14, tr[Pg.16]

For toluene, for example, the value 0 for the electric dipole moment would be expected if the methyl group were attached to the ring by a normal single bond and the C—H bonds of the group and the rhift had the same amount of ionic character. The observed value, 0.37 D, indicates that structures of the type... 

Arsenic triiodide is soluble in carbon disulphide, alcohol, ether, chloroform, benzene, toluene and the xylenes.5 The solution in carbon disulphide gradually darkens owing to absorption of oxygen and liberation of iodine.6 With alcohol at 150° C. ethyl iodide is formed. In methylene iodide 5 the triiodide dissolves to the extent of 17-4 parts of AsI3 in 100 parts of solvent at 12° C. The dipole moment in various solvents has been determined.7... 

In-plane and out-of-plane rotational dynamics of CigRB at the toluene/water interface was evaluated using time-resolved TIR fluorescence spectroscopy [27]. The known transition dipole moment for the absorption of rhodamine B(RB) at about 530 nm (So Si) is almost parallel to that for the emission at about 570 nm (Si -> So) [28]. Time-resolved in-plane fluorescence anisotropy (r[Pg.213]

Inspection of Table 4-9 reveals that the axial cis isomer (34a), which is the con-former with the higher dipole moment, becomes more favoured as the solvent polarity increases. In the most polar solvent studied, acetonitrile, AG° is nearly zero. Benzene, toluene, trichloromethane, dichloromethane, and methanol are seen to behave as more polar solvents than their relative permittivities would lead one to predict. The deviation for trichloromethane was particularly dilficult to explain (for a full discussion, see reference [89]). In general, good correlations between values and other solvent-... 

The ratio of cis and trans isomers formed depends on L and the solvent. The cis isomer has a dipole moment and is better solvated in polar media hence the relative concentration of cis isomer increases on going from toluene to acetone. In a given solvent the cis geometry is more favored for L = PMej than for L = PEtj. 

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