Probe homomorph couple

Replacement of the acid proton (N-H) by a methyl group in this molecular structure has the same side effects as a result, the compound will be similarly sensitive to the polarity and acidity of the medium, but not to its basicity owing to the absence of an acid site. Consequently, l-methyl-5-nitroindoline (MNI, 10) possesses the required properties for use as a homomorph of 5-nitroindoline in order to construct our solvent basicity scale (SB). The suitability of this probe/homomorph couple is consistent with theoretical MP2/6-31G data. Thus, both the probe and its homomorph exhibit the same sensitivity to solvent polar-ity/polarizability because of their similar dipole moments (p i = 7.13, = 7.31 D) and... 

These results show that an oxygen lone pair in (11) is basic enough, as a result of hydrogen bonding, for (11) to be used as an acidity probe in UV-Vis spectroscopy thus, the absorption maximum for TBSB shifts by about 1000 cm from 1-decanol to ethanol, whereas that for DTBSB shifts by only 300 cm. This sensitivity to acidity, and the structural likeness of the probe and its homomorph -which must endow them with a similar sensitivity to solvent basicity and dipolarity/polarizability-, suggest that the two compounds make an appropriate probe-homomorph couple for developing a pure solvent acidity scale. For this purpose, the first visible absorption band for these compounds exhibits quite an in-... 

The SA value of an acid solvent as determined using the DETZ probe is calculated using the expression established from the information provided by a series of solvents of increased acidity measurable by the TBSB/DTBSB probe/homomorph couple (viz. 1,2-butanediol, 1,3,-butanediol, ethanol, methanol and hexafluoro-2-propanol) this gives rise to eq. [10.3.14], which, in principle, should only be used to determine SA for solvents with Avr,FT7 values above 100 cm" ... 

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