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Correlation analysis of UV spectral data of some phenylhydrazones and semicarbazones by the dual‐parameter equation. Observation of three types of behaviors of the λ max values induced by the polar effects of substituents
Author(s) -
Ding William FaXiang,
Jiang XiKui
Publication year - 1998
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(1998110)11:11<809::aid-poc71>3.0.co;2-1
Subject(s) - bathochromic shift , hypsochromic shift , chemistry , delocalized electron , enthalpy , polar effect , polar , crystallography , stereochemistry , computational chemistry , photochemistry , fluorescence , organic chemistry , physics , quantum mechanics , astronomy
The K‐band λ max values of the UV spectra of five types of p ‐Y‐benzaldehyde derivatives, namely phenylhydrazones ( 1 ‐Ys), 2,4‐dinitrophenylhydrazones ( 2 ‐Ys), 4‐nitrophenylhydrazones ( 3 ‐Ys), semicarbazones ( 4 ‐Ys) and N ‐phenylsemicarbazones ( 5 ‐Ys), were measured and the corresponding wavenumbers (ν max ) calculated. Correlation analyses of the ν max values by the dual‐parameter equation show that the ν max values of these compounds are affected, albeit to different degrees, by both spin‐delocalization effects (σ ˙ ) and polar effects (σ x ) of the substituents. The spin‐delocalization effects of substituents always facilitate bathochromic shifts of the λ max values (ρ ˙ negative). However, polar effects of the substituents on these λ max data depend on the mode of polarization of these hydrazone or semicarbazone molecules, i.e. electron‐pair acceptor substituents (Ys) facilitate bathochromic shifts for 1 ‐Ys (ρ x negative), but hypsochromic shifts for 2 ‐Ys and 3 ‐Ys (ρ x positive), and induce very small shifts for 4 ‐Ys and 5 ‐Ys. As expected, donor Ys facilitate hypsochromic shifts for 1 ‐Ys and bathochromic shifts for 2 ‐Ys and 3 ‐Ys and induce very small shifts for 4 ‐Ys and 5 ‐Ys. Possibly, a higher degree of polarization of the substrate molecule would demand a higher degree of polar assistance from the substituents at the transition states. © 1998 John Wiley & Sons, Ltd.