Six series of styrene derivatives XCH═CHArY (total of 65) containing the styrene parent molecular skeleton were synthesized (here, Y is OMe, Me, H, F, Cl, CF3, CN, and NO2, and X is 2‐furyl, 3‐furyl, 2′‐methyl‐2‐furyl, 2‐thienyl, 3‐thienyl, and 2′‐methyl‐2‐theniyl). Their ultraviolet absorption spectra were measured in anhydrous ethanol, and their wavelength of absorption maximum λmax was recorded. For the wavenumber νmax (cm−1, νmax = 1/λmax) of the obtained λmax, a quantitative correlation analysis was performed, and 6 excited‐state substituent constants
σCC()pex of groups X were obtained by means of curve‐fitting method. Taking the νmax values of total 90 compounds of styrene derivatives as a data set (including 25 compounds from reference and 65 compounds of this work), a quantitative correlation analysis was performed, and the reliability of the obtained
σCC()pex was verified. In addition, 12 samples of disubstituted Schiff bases (XCH═NArY) involving the above groups X were synthesized, and their νmax values were recorded. Using these 12 νmax together with the 14 νmax values of Schiff bases taken from reference (total of 26 compounds), it was further verified that the
σCC()pex values are reliable by means of quantitative correlation method.
For studying the substituent effects on the ν max of substituted benzylideneanilines (XBAYs) systematically, 12 samples of 3,3′-disubstituted XBAYs and 52 samples of multi-substituted XBAYs were synthesized, and the substituent effects on their ν max were investigated in this paper. A modified regression equation quantifying the ν max of 4,4′/4,3′/3,4′/3,3′-disubstituted and multi-substituted XBAYs (shown as Eq. 3) was obtained. The results showed that the substituent effects on the ν max of 3,3′-substituted and multi-substituted XBAYs became more complicated. In Eq. 3, the contributions of the meta-parameters to the ν max of XBAYs were different from those of the corresponding para-parameters. For the substituent cross-interaction effects, there is no difference whatever the substituents are at meta-position or para-position. Compared with Eq. 1, Eq. 3 obtained in this paper has a wider application and more accuracy in quantifying the ν max of substituted XBAYs.
Changes in various physicochemical properties (
P
(
n
)
) of organic compounds with
the number
of carbon atoms (
n
) can be roughly divided into linear
and nonlinear changes. To date, there has been no general equation
to express nonlinear changes in the properties of organic homologues.
This study proposes a general equation expressing nonlinear changes
in the physicochemical properties of organic homologues, including
boiling point, viscosity, ionization potential, and vapor pressure,
named the “NPOH equation”, as follows:
P
(n)
=
P
(1)
α
n – 1
e
∑
i=2
n
(
β
/(
i
– 1))
where α and β are adjustable parameters, and
P
(1)
represents the property of the starting
compound (pseudo-value at
n
= 1) of each homologue.
The results show that various nonlinear changes in the properties
of homologues can be expressed by the NPOH equation. Linear and nonlinear
changes in the properties of homologues can all be correlated with
n
and the “sum of carbon number effects”,
∑
i=2
n
(1/i – 1). Using these two parameters, a quantitative correlation
equation can be established between any two properties of each homologue,
providing convenient mutual estimation of the properties of a homologue
series. The NPOH equation can also be used in property correlation
for structures with functionality located elsewhere along a linear
alkyl chain as well as for branched organic compounds. This work can
provide new perspectives for studying quantitative structure–property
relationships.
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