Dipole moments of some substituted benzaldehydes. Conformational preference of substituents ortho to the aldehyde group |
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Authors: | V Baliah and T Chellathurai |
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Institution: | (1) Department of Chemistry, Annamalai University, 608 002 Annamalainagar, India;(2) Present address: 79. 3rd Cross Road, Venkatanagar, 605011 Pondicherry, India |
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Abstract: | The dipole moments of a number of substituted benzaldehydes are measured in benzene solution. The angle which the dipole axis
of the CHO group makes with the axis of rotation of the group is determined. The observed moments of the ortho-substituted
benzaldehydes are compared with the moments calculated for free rotation as well as fors-trans ands-cis orientations of the -CHO group.o-Fluorobenzaldehyde exists mostly in thes-trans conformation.o-Chloro-,o-bromo-ando-nitro-benzaldehydcs also exist in thes-trans conformation; their observed dipole moments are even lower than the values calculated fors-trans forms, indicating mutual induction of the ortho substituents. Though 2,5-dichlorobenzaldehyde is expected to have the same
dipole moment as benzaldehyde, the observed moment is significantly lower due to mutual induction of the ortho substituents.
2,5-Dimethylbcnzaldehyde has, however, almost the same moment as benzaldehyde. The dipole moment ofo-methoxybcnzaldchyde is considerably higher than the values calculated for boths-cis ands-trans conformations. An explanation is given for this.o-Hydroxybenzaldehyde exists exclusively in thes-cis form due to internal H-bonding. |
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Keywords: | Dipole moments of benzaldehydes conformational preference ofo-substituted benzaldehydes dipole angle of -CHO group mutual induction |
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