IR spectroscopic studies on the transmission of substituent effects to carbonyl and thiocarbonyl stretching frequencies in 4-substituted phenyl-4,5-dihydrobenzo [f] [1,4] oxazepin-3 (2H)-ones (thiones)
Introduction
Infrared (IR) spectroscopy is a powerful tool for the quantitative study of natural and synthetic molecules [1]. IR spectroscopy can provide information about the nature, concentration and structure of samples at the molecular levels.
It is well demonstrated in the literature [2], [3], [4], [5], [6], [7], [8], [9] that infrared (IR) stretching frequencies are sensitive probes of electron-density distributions and are useful for studies on the transmission of electronic effects in organic molecules.
Compounds containing the carbonyl group present a strong absorption band in the infrared region, placed within 1928 and 1515 cm−1, referring to the stretching vibration of the CO bond, ν(CO). The terminal value of the force constants of this bond, minimize couplings with adjacent groups, while its polarizability turns it susceptible to the effects coming from its surroundings [10], [11]. Therefore, the accurate position of the CO group absorption band in the IR is result of the action of intermolecular and intramolecular factors, mainly of the electronic influence of substituent groups. Hence, variations in the absorption ν(CO) band position in the IR region can be considered as being the result of the polar effects of the substituent groups.
The benzoxazepines with carbonyl groups have shown anxiolytic [12], central depressant [13], analgesic [14], local anesthetic [15], anti-inflammatory [16] and antihistaminic [17] effects. So, it is expected that also the title compounds will exhibit various physiological effects. The aim of this study is the IR investigation on transmission of electronic effects by substituents in a series of 4-substituted phenyl-4,5-dihydrobenzo [f] [1,4] oxazepin-3 (2H)-ones (5a–n) (Scheme 1) which can be further used in evaluation of the mechanisms of the physiological action of these compounds.
Additionally, we have also studied the transmission of substituent effects on IR thiocarbonyl stretching frequencies ν(CS) of 4-substituted phenyl-4,5-dihydrobenzo [f] [1,4] oxazepin-3 (2H)-thiones (6a–n) (Scheme 1). Substituent effects on CO [2], [3], [4], [6], [7], [8], [10], [11], CN [5], SO2 [4], [8] and N–H [8], [9] stretching frequencies have been studied previously. However, as far as we know, a substituent effect study on IR ν(CS) is not present in the literature.
We also performed density functional theory (DFT) calculations on compounds (5) and (6) to characterize their three-dimensional structures and to predict their carbonyl and thiocarbonyl stretching frequencies.
Section snippets
Experimental
Schiff bases (2) (Scheme 1) were synthesized according to the literature [18]. The bands for the azomethine groups of (2) were observed in the IR spectra at about 1620 cm−1. For the synthesis of compounds (3–6), literature methods [19], [20], [21] were applied with slight modifications.
Salicylaldehyde (1) was reacted with substituted aniline to afford 2-[(E)-(substituted phenylimino) methylphenols (2) which were reduced by NaBH4 to obtain 2-(substituted phenylamino) phenols (3). Compounds (3)
IR spectral study
The IR ν(CO) and ν(CS) of compounds (5a–n) and (6a–n), respectively are listed in Table 1. The low ν(CO) and ν(CS) were observed.
When strong electron donating groups were present in the phenyl ring. Contrarily, high frequencies were noted when strong electron attracting groups were present in the same ring (Fig. 1, Fig. 2). A similar trend in the absorption was also observed earlier [2], [3], [4], [6].
ν(CO) of compounds (5a–n) provide fair correlation with σ and a better correlation with
Conclusions
It has been shown that substituent effects from the aryl group are efficiently transmitted to the heterocyclic framework of compounds (5) and (6). This transmission has been characterized by fair correlations between the Hammett-type constants of the substituents and CO (or CS) stretching wave numbers of the seven-membered heterocyclic ring system.
Acknowledgement
The authors thank Kocaeli University Research Fund for financial support (Grant No. 2004/34).
References (26)
- et al.
J. Mol. Struct.
(2004) - et al.
Spectrochim. Acta Part A
(2007) - et al.
J. Mol. Struct.
(2007) - et al.
Spectrochim. Acta Part A
(1997) - et al.
Spectrochim. Acta Part A
(2003) - et al.
Bioorg. Med. Chem.
(2004) - et al.
J. Mol. Struct.
(2008) - et al.(2002)
- et al.
Molecules
(2004) - et al.
J. Serb. Chem. Soc.
(2007)
J. Org. Chem.
Spectrochim. Acta
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2013, Chemical Industry and Chemical Engineering Quarterly