Since 1990’s chemists are paying much more interest in the application of solvent free synthetic methods1 in organic reactions like Claisen2-Schmidt, Knovenogal3, Aldol4 and Crossed-aldol5 employed for synthesis of carbonyl compounds due to the operational simplicity, easier work-up, better yield and eco-friendly nature. Among these reactions aldol condensation is useful for the formation of carboncarbon bond in many kinds of carbonyl compounds.6 The basic skeleton of chalcones and antibiotics are widely figured in natural products, are known to have multipronged activity.7,8 Many of the chalcones are used as agrochemicals and drugs.9 Condensation of ketones with aldehydes is special interest and crossed-aldol condensation is an effective pathway for those preparations. But traditional acid-base catalyzed reactions suffer from the reverse reaction10 and self condensation of starting molecules.11
Many reagents and Co-ordination complexes of Mn (II), Fe (II), Co (II), Ni (II), Cu (II) and Zn (II) ions with various ligands have been employed for aldol condensation.12 Metal salts of Cp2ZrH2 are used for condensation of cycloalkanones.13 KF-Al2O3 and bis (p-methoxy phenyl) tellurides have been used for crossed condensation under microwave irradiation.14 Anhydrous RuCl3 and TiCl3 (SO3CF3) have also been applied for aldol condensation reactions under solvent free conditions.15 Now more attention has been paid to synthesis of acyclic and cyclic chalcones by chemists and scientists.16 Balakrishna Kalluraya17 et al. reported to obtain 60-70% yield of sydnone chalcones under solvent free condition by aldol condensation reaction by grinding of ketones and aldehydes with sodium hydroxide. Mohamed A. Hassan et al.18 synthesized various 2E-3-aryl-1-hetarylprop-2-en-1-ones by eco-friendly condensation reaction in sodium hydroxide-water heterogeneous phase reaction medium. Silica-sulphuric acid is used as a versatile and stable solid acid catalyst for organic synthesis. The author wish to report an efficient and selective method for condensation of 6-methoxy-2-naphthyl ketones with various m- and p-substituted benzaldehydes under solvent free conditions using silica-sulphuric acid as a reagent in an oven to yields the respective E-2-propen-1-ones. The promoting effect of silica – sulphuric acid in their reaction was shown good performance and it is proved by obtaining higher percentage of yields. The product was isolated and the remaining catalyst was washed and reused with fresh substrate for further reactions. No decrease in the yield was observed, demonstrating that silica-sulphuric acid can be reused in crossed-aldol condensation reaction without environmental discharge.
Materials and Methods
All chemicals and Analytical Grade solvents were purchased from E-Merck chemical company. Melting points of all chalcones were determined in open glass capillaries on Mettler FP51 melting point apparatus and are uncorrected. Infrared spectra (KBr, 4000-400 cm-1) were recorded on Perkin Elmer-Fourier transform spectrophotometer. The nuclear magnetic resonance spectra both 1H and 13C of chalcones were recorded using UNITYPLUS-300 “KIBSIPS” 300MHz spectrometer. Electron impact (EI) (70 eV) and chemical ionization (CI) were recorded with a Finnigan MAT 95S spectrometer. Micro analyses of all chalcones were performed in Perkin Elmer 240C Analyzer.
General procedure for synthesis of substituted styryl 6-methoxy-2-naphthyl ketones
6-Methoxy-2-naphthyl ketones (2 mmol), m-and p-substituted benzaldehydes (4.2 mmol) and silicasulphuric acid (1.5 g equal to 4 mmol of H+) were mixed thoroughly, placed in a glass tube and capped (Scheme 1). The mixture was heated in an oven at 80 ℃ for 2-3.5 h. After complete conversion of the ketones as monitored by TLC, the mixture was cooled to room temperature. Dichloromethane (20-30ml) was added and heated for 3-5 minutes. The reagent was removed by filtration. The filtrate was concentrated and the solid residue was recrystallised from ethanol to afford the pure products as pale yellow glittering solid19 (1a-m). The catalyst was recycled by washing the solid reagent remained on the filter by ethyl acetate (20 ml) followed by drying in an oven at 50 ℃ for 2 h and it can be reusable for another reaction run. Based on Hays and Timmons20,21 infrared carbonyl stretching frequencies of s-cis and s-trans conformers are assigned. The NMR chemical shifts (ppm) of ethylene α, β protons and carbons are assigned based on reported in earlier literature values.22-27 The characterization data of all chalcones are summarized.
1a. (2E)-1-(6-Methoxy-2-naphthyl)-3-phenyl-2-propen-1-one. Yield: 96%; m.p.67-69(69-7020)℃; IR (KBr, cm-1): ν=1665 (CO s-cis), 1626 (CO s-trans), 993(CH=CH); 1H NMR(CDCl3, ppm): δ=7.612(d, 1H, α), 7.766(d,1H, β), 6.711-7.482(m, 11H Ar-H), 3.821(s, 3H -OCH3); 13C NMR(CDCl3, ppm): δ=119.460(Cα) 144.628(Cβ), 182.105(CO), 128.420(C1), 132.760(C2), 124.711(C3), 127.110(C4), 104.992(C5), 159.320(C6), 119.553(C7), 130.993(C8), 133.499(C4a), 131.299(C8a), 56.235(-OCH3), 135.934(C1'), 126.421(C2', 6'), 127.989(C3',5'), 128.101(C6'). C20H16O2. MS: m/z=288[M+], 185,158, 136, 131,128, 103, 91, 77, 65.
1b. (2E)-1-(6-Methoxy-1-naphthyl)-3-(3-aminophenyl)-2-propen-1-one. Yield: 94%; m.p. 97-98℃; IR (KBr, cm-1): ν=1667 (CO s-cis), 1622 (CO s-trans), 985(CH=CH), 3533(-NH2). 1H NMR (CDCl3, ppm): δ=7.554(d, 1H, α), 7.823(d, 1H, β), 6.811-7.342(m, 10H, Ar-H), 4.570(s, 2H –NH2), 3.633(s, 3H -OCH3). 13C NMR (CDCl3, ppm): δ=119.240(Cα) 144.527(Cβ), 187.220(CO). 128.423(C1), 132.763(C2), 124.698(C3), 127.320(C4), 104.902(C5), 159.243(C6), 119.583(C7), 130.932(C8), 133.475(C4a), 131.309(C8a), 56.993(-OCH3), 136.091(C1'), 111.421(C2'), 148.279(C3'), 116.010(C4'), 129.498(C5'), 116.412C6'). Anal. Calcd. for C20H17NO2: C, 79.19; H, 5.65; N, 4.62. Found: C, 79.13; H, 5.46; N, 4.60. MS: m/z=303[M+], 287,272,185,158, 136,128, 118, 102, 93.
1c. (2E)-1-(6-Methoxy-2-naphthyl)-3-(4-aminophenyl)-2-propen-1-one. Yield: 96%; m.p. 86-87℃; IR (KBr, cm-1): ν=1660 (CO s-cis), 1627 (CO s-trans), 985(CH=CH), 3528(-NH2). 1H NMR (CDCl3, ppm): δ=7.234(d, 1H α), 7.672(d, 1H, β), 6.767-7.201(m, 10H, Ar-H), 4.671(s, 2H -NH2), 3.479(-OCH3). 13C NMR (CDCl3, ppm): δ=118.770(Cα) 144.224(Cβ), 185.340(CO), 127.994(C1), 132.653(C2), 124.721(C3), 127.381(C4), 106.002(C5), 159.497(C6), 119.498(C7), 130.995(C8), 133.963(C4a), 132.003(C8a), 56.064(-OCH3), 125.043(C1'), 126.995(C2',6'), 117.009(C3',5'), 146.994(C4'). Anal. Calcd. for C20H17NO2: C, 79.19; H, 5.65; N, 4.62. Found: C, 79.16; H, 5.59; N, 5.57. MS: m/z=303[M+], 185, 158, 136, 128, 118, 102, 77, 93.
1d. (2E)-1-(6-Methoxy-2-naphthyl)-3-(3-bromophenyl)-2-propen-1-one. Yield: 95%; m.p. 114-115℃; IR(KBr, cm-1): ν=1674 (CO s-cis), 1633 (CO s-trans), 978(CH=CH). 1H NMR(CDCl3, ppm): δ=7.727(d,1H, α), 7.891(d,1H, β), 7.041-7.644(m, 10H Ar-H), 3.595(s, 3H –OCH3). 13C NMR (CDCl3, ppm): δ=119.642(Cα), 144.748(Cβ), 188.796(CO), 128.475(C1), 133.201(C2), 124.021(C3), 127.098(C4), 106.490(C5), 159.782(C6), 120.991(C7), 130.995(C8), 133.453(C4a), 131.396(C8a), 56.632(-OCH3), 136.994(C1'), 129.899(C2'), 123.643(C3'), 131.010(C4'), 129.996(C5'), 125.949C6'). Anal. Calcd. for C20H15BrO2: C, 65.41; H, 4.12. Found: C, 65.36; H, 4.09. MS m/z=367 [M+, Br80.9], 365 [M+, Br79.9], 287, 285, 188, 186, 182, 180, 169, 167, 156, 154, 136, 89, 91, 77, 65.
1e. (2E)-1-(6-Methoxy-2-naphthyl)-3-(3-chlorophenyl)-2-propen-1-one. Yield: 92%; m.p. 101-102℃; IR (KBr, cm-1): ν=1671 (CO s-cis), 1628 (CO s-trans), 965(CH=CH). 1H NMR (CDCl3, ppm): δ=7.981(d, 1H, α), 8.112(d, 1H, β), 7.261-7.924(m, 10H, Ar-H), 3.328 (s, 3H -OCH3). 13C NMR (CDCl3, ppm): δ=119.527(Cα) 144.664(Cβ), 190.193(CO), 127.979(C1), 133.342(C2), 124.443(C3), 127.954(C4), 105.996(C5), 159.236(C6), 120.191(C7), 131.099(C8), 133.634(C4a), 131.702(C8a), 54.247(-OCH3), 136.798(C1'), 126.955(C2'), 134.199(C3'), 127.997(C4'), 129.996(C5'), 124.549C6'). Anal. Calcd. for C20H15ClO2: C, 74.42; H, 4.68. Found: C, 74.38; H, 4.61. MS: m/z=324[M+,Cl37], 322[M+, Cl35], 289, 287, 187, 185, 139, 138, 137, 136, 113, 111, 93, 91, 79, 77, 67, 65, 53, 51.
1f. (2E)-1-(6-Methoxy-2-naphthyl)-3-(4-chlorophenyl)-2-propen-1-one. Yield: 93%; m.p. 122-123℃; IR (KBr, cm-1): ν=1664 (CO s-cis), 1634 (CO s-trans), 1015(CH=CH). 1H NMR (CDCl3, ppm): δ=7.905(d, 1H, α), 7.992(d, 1H, β), 7.143-7.870(m, 10H, Ar-H), 3.543 (-OCH3); 13C NMR(CDCl3, ppm): δ=119.401(Cα) 141.822(Cβ), 188.230(CO), 127.644(C1), 132.843(C2), 124.3831(C3), 127.942(C4), 106.502(C5), 159.721(C6), 119.128(C7), 130.931(C8), 133.932(C4a), 132.732(C8a), 55.648(-OCH3), 133.399(C1'), 127.992(C2',6'), 128.964 (C3',5'), 134.974(C4'). Anal. Calcd. for C20H15ClO2: C, 74.42; H, 4.68. Found: C, 74.40; H, 4.64. MS m/z=324[M+, Cl37], 322[M+, Cl35], 289, 287, 187, 160, 158, 139, 138, 136, 113, 93, 91, 79, 67, 65.
1g. (2E)-1-(6-Methoxy-2-naphthyl)-3-(4-dimethylaminophenyl)-2-propen-1-one. Yield: 95%; m.p. 142-143℃; IR(KBr, cm-1): ν=1655 (CO s-cis), 1624 (CO s-trans), 1008(CH=CH); 1H NMR(CDCl3, ppm): δ=7.167(d,1H, α), 7.737(d, 1H, β), 6.803-7.081(m, 10H, Ar-H), 3.874(s, 3H -OCH3), 2.878(s, 6H -(CH3)2). 13C NMR (CDCl3, ppm): δ=118.475(Cα) 144.059(Cβ), 187.021(CO), 127.979(C1), 132.498(C2), 124.967(C3), 127.064(C4), 106.764(C5), 159.543(C6), 119.398(C7), 132.012(C8), 133.643(C4a), 132.298(C8a), 56.023(-OCH3), 124.699(C1'), 127.339(C2',6'), 115.227(C3',5'), 148.997(C4'). 41.043(-(CH3)2). Anal. Calcd. for C22H21NO2: C, 79.73; H, 6.39; N, 4.23. Found: C, 79.68; H, 6.27; N, 4.19. MS: m/z=331[M+], 316, 287, 185, 158, 146, 136, 134, 120, 91, 65.
1h. (2E)-1-(6-Methoxy-2-naphthyl)-3-(4-hydroxyphenyl)-2-propen-1-one. Yield: 91%; m.p. 117-118℃; IR (KBr, cm-1): ν=1657 (CO s-cis), 1633 (CO s-trans), 983(CH=CH), 3498(-OH). 1H NMR (CDCl3, ppm): δ=7.197(d, 1H, α), 7.737(d, 1H, β), 6.269-7.013(m, 10H, Ar-H), 4.788(s, 1H -OH), 3.576(-OCH3). 13C NMR (CDCl3, ppm): δ=118.927(Cα) 144.246(Cβ), 190.242(CO), 128.326(C1), 132.496(C2), 124.653(C3), 127.091(C4), 105.555(C5), 159.608(C6), 119.604(C7), 131.852(C8), 133.591(C4a), 132.091(C8a), 56.601(-OCH3), 127.003(C1'), 127.890(C2',6'), 115.974(C3',5'), 158.004(C4'). Anal. Calcd. for C20H16O3: C, 78.93; H, 5.30. Found: C, 78.19; H, 5.25. MS: m/z=294[M+], 277, 258, 185, 168, 140, 128, 124, 107, 102, 91, 77, 65.
1i. (2E)-1-(6-Methoxy-2-naphthyl)-3-(4-methoxyphenyl)-2-propen-1-one. Yield: 94%; m.p. 107-108 °C; IR(KBr, cm-1): ν=1655 (CO s-cis), 1628 (CO s-trans), 995(CH=CH); 1H NMR(CDCl3, ppm): δ=7.197(d,1H, α), 7.822(d,1H, β), 6.910-7.034(m, 10H, Ar-H), 3.6726(s, 6H -OCH3). 13C NMR (CDCl3, ppm): δ=119.442(Cα), 144.246(Cβ), 192.203(CO), 127.998(C1), 132.967(C2), 124.704(C3), 127.096(C4), 105.504(C5), 159.623(C6), 119.479(C7), 131.443(C8), 133.864(C4a), 132.442(C8a), 54.758(-OCH3), 127.596(C1'), 127.339(C2',6'), 114.099(C3',5'), 158.996(C4'), 55.993(-OCH3, Ph), Anal. Calcd. for C21H18O3: Anal. C, 81.79; H, 6.10. Found: C, 81.74; H, 5.98. MS: m/z=317[M+], 185, 158,136, 131, 128, 93, 91, 77, 65.
1j. (2E)-1-(6-Methoxy-2-naphthyl)-3-(4-methylphenyl)-2-propen-1-one. Yield: 95%; m.p. 87-88℃; IR (KBr, cm-1): ν=1662 (CO s-cis), 1621 (CO s-trans), 998(CH=CH). 1H NMR (CDCl3, ppm): δ=7.511(d, 1H, α), 7.763(d, 1H, β), 6.327-7.354(m, 10H, Ar-H), 3.394(s, 3H -OCH3), 2.424(s, 3H -CH3). 13C NMR(CDCl3, ppm): δ=119.199(Cα) 144.362(Cβ), 187.902(CO), 128.546(C1), 132.465(C2), 125.096(C3), 127.433(C4), 105.843(C5), 159.965(C6), 119.597(C7), 131.009(C8), 133.663(C4a), 132.006(C8a), 54.421(-OCH3), 132.922(C1'), 127.001(C2',6'), 129.111(C3',5'), 138.956(C4'), 25.901(CH3). Anal. Calcd. for C21H18O2: C, 87.06; H, 6.49. Found: C, 86.98; H, 6.39. MS: m/z=301[M+], 286, 185, 158, 136, 128, 118, 102, 91, 65.
1k. (2E)-1-(6-Methoxy-2-naphthyl)-3-(2-nitrophenyl)-2-propen-1-one. Yield: 94%; m.p. 92-93℃; IR(KBr, cm-1): ν=1679(CO s-cis), 1646 (CO s-trans), 1015(CH=CH); 1H NMR(CDCl3, ppm): δ=8.062(d,1H, α), 8.142(d,1H, β), 6.440-7.869(m, 10H. Ar-H), 3.295(s, 3H -OCH3). 13C NMR(CDCl3, ppm): δ=119.934(Cα), 145.242(Cβ), 186.458(CO), 128.936(C1), 132.382(C2), 124.674(C3), 127.632(C4), 105.361(C5), 159.654(C6), 119.009(C7), 131.996(C8), 133.487(C4a), 131.921(C8a), 54.247(-OCH3), 130.098(C1'), 146.095(C2'), 120.909(C3'), 128.899(C4'), 134,799(C5'), 127.338(C6'). Anal. Calcd. for C20H15NO4: C, 87.06; H, 6.49; N, 4.34. Found: C, 86.92; H, 6.42; 4.29. MS: m/z=333[M+], 287, 158, 148, 136, 77, 65.
1l. (2E)-1-(6-methoxy-2-naphthyl)-3-(3-nitrophenyl)-2-propen-1-one Yield: 95%; m.p. 133-134℃; IR(KBr, cm-1): ν=1675 (CO s-cis), 1642 (CO s-trans), 1013(CH=CH).; 1H NMR(CDCl3, ppm): δ=8.114(d,1H, α), 8.154(d,1H, β), 7.051-8.021(m, 10H, Ar-H), 3.803(s, 3H –OCH3). 13C NMR (CDCl3, ppm): δ=119.843(Cα), 145.314(Cβ), 191.025(CO), 128.091(C1), 133.455(C2), 124.761(C3), 127.091(C4), 105.601(C5), 159.765(C6), 120.009(C7), 131.109(C8), 133.554(C4a), 131.334(C8a), 56.297(-OCH3), 136.117(C1'), 121.295(C2'), 148.419(C3'), 120.932(C4'), 129.765(C5'), 132.245(C6'). Anal. Calcd. for C20H15NO4: C, 87.06; H, 6.49; N, 4.34. Found: C, 86.90; H, 6.42; 4.25.MS: m/z=333[M+], 185, 287, 158, 148, 136, 128, 91, 77, 65.
1m. (2E)-1-(6-methoxy-2-naphthyl)-3-(4-nitrolphenyl)-2-propen-1-one. Yield: 95%; m.p. 148-149℃; IR(KBr, cm-1): ν=1677 (CO s-cis), 1640 (CO s-trans), 1018(CH=CH). 1H NMR(CDCl3, ppm): δ=8.157(d,1H, α), 8.206(d,1H, β), 7.461-8.044(m, 10H, Ar-H), 3.630(s, 3H -OCH3). 13C NMR (CDCl3, ppm): δ=119.927(Cα), 144.942(Cβ), 191.843(CO), 128.499(C1), 132.621(C2), 124.895(C3), 127.461(C4), 105.551(C5), 159.698(C6), 119.553(C7), 131.101(C8), 133.509(C4a), 131.309(C8a), 55.720(-OCH3), 141.397(C1'), 127.309(C2', 6'), 120.832(C3', 5'), 148.009(C4'), Anal. Cacld. for C20H15NO4: C, 87.06; H, 6.49; N, 4.34 Found: C, 87.01; H, 6.45; 4.31. MS: m/z=333[M+], 185,287, 158, 148, 136, 131, 128, 91, 77, 65.
Previous investigations of substituted styryl 4-methoxy 1-naphthyl chalcones includes the synthesis and identification of new compounds,28 and the study of new catalysts for obtaining the chalcones. The spectral data of these types of chalcones have been investigated. Other investigators studied the tautomerism of some substituted carbonyl compounds by spectral data.29 These papers and other communications were reported in earlier and recent publication.
It is well known from the literature that the chalcones of structure similar to those investigated here have a broad spectrum of biological activity30 and to mentions only a few exhibited vasodilatory, antioxidant, antidiabetic, antimicrobial and antiviral activity. Therefore we considered it worthwhile to investigate the effects of substituents in this title of the compounds in Scheme 1. On the spectral features of the groups in investigated molecules which might be either directly or indirectly in molecular interactions in living organisms.
A large number of spectral data relating to substituted styryl naphthyl chalcones accumulated in the previous investigations, were correlated in the present work using a variety of LFER models, conventionally used for the study of structure – reactivity and structure-property relationships. It was assumed that it should be possible to find an adequate approach to study the transmission of substituent effects in the multi-substituted chalcones, considering that their aromaticity has been established. It was always initially attempted to use a simple Hammett Equations as presented in Eq. 1.a., but it was frequently more appropriate to use other approaches, like the Hammett-Taft (Extended Hammett Equation) DSP model, Eq. 1.b., and Swain-Lupton Eq. 1.c., which are usually given in the literature in their general form.31
In these models, the author applied Eq. 1. a. and c. only for evaluation of electronic effects in this aromatic system and s is the measured spectral characteristics, σm/p, σI, σR, F and R32 are substituent constants, ρ, ρI, ρR, ƒ and r are the corresponding calculated proportionality constants, which in a broad sense reflect the sensitivity of the spectral characteristics to substituent effects and so is the intercept. On certain occasions, when other model failed, combined multiparameter equations were applied, the method known to be used before and with the same precision as obtained here.
Correlation analysis from infrared spectral data
From infrared spectra of all chalcones the carbonyl stretching frequencies (cm-1) of s-cis and s-trans conformers are assigned are presented in Table 1 and the corresponding isomers are shown in (I). The infrared spectra were all recorded on the KBr disc in order to avoid the shoulder formation33 on carbonyl doublets. The s-cis conformers exhibit higher frequencies than the s-trans conformers due to the bulkier naphthalene group causes greater strain and they enhance the higher absorption of carbonyl group of s-cis isomer than the s-trans isomer. These frequencies are separately analyzed through various Hammett sigma constants.
Table 1.Infra red νC=O (cm-1) frequencies of s-cis and s-trans conformers, 1H chemical shifts (ppm) of H-α and H-β protons and 13C chemical shifts (ppm) of C-α and C-β carbons of in substituted styryl 6-methoxy 2-naphthyl ketones
From the statistical analysis34, there is a fair correlation(r=0.917) obtained with Hammett σ constants. And no significant correlation obtained with Hammett σ+, σI, and σR constants in s-cis isomers. The poor correlation is due to hindred rotation between styryl and the naphthyl moiety. In s-trans isomers σI constants gave a fair correlation(r=0.915) with the carbonyl frequencies of the chalcones and other constants are failure for production of correlation. Because, the expected conjugation between the –CH=CH- and the C=O groups is missing in the s-trans isomers and the restriction of free rotation of the bulkier naphthyl group affects hyper conjugational resonance interaction shown in (II). Single parameter correlation is shown in Fig. 1 and 2. The generated correlation equations (2, 3) are;
Fig. 1.Plot of νC=O (s-cis) of substituted styryl 6-methoxy-2-naphthyl ketones versus σ.
Fig. 2.Plot of νC=O (s-trans) of substituted styryl 6-methoxy-2-naphthyl ketones versus σI.
Similarly the collective correlation of σI, σR, or F and R constants with these frequencies are failed to produce the correlation in s-cis carbonyl frequencies of these chalcones. But the correlation was also performed σI and σR constants with s-trans carbonyl frequencies of the all chalcones generated the correlation equation (4) is,
Correlation analysis from NMR spectral data 1H NMR Spectra
The 1H NMR spectral signals of ethylenic protons in all chalcones investigated are assigned.35 The ethylenic protons near the carbonyl group in Scheme 1 are termed as Hα and those next to Hα are termed as Hβ. The chemical shifts of Hα protons are at higher field than those of Hβ protons in all chalcones. The ethylenic proton signals give an AB pattern and the β protons doublet in most cases is well separated from the signals of the aromatic protons. The chemical shifts of α, β protons are given in Table 1. The observation that Hα protons appear at higher field than that of Hβ protons makes the subject very interesting. This may possibly due to the polarization of C=C double bond in the system being predominantly caused by the carbonyl group so as to make electron density greater at the α position than that of β position.
Table 2.Where r = Correlation coefficient, I = Intercept, ρ = Slope, s = Standard deviation and n = Number of substituents correlated.
The results of statistical analysis are presented in Table 2. All the attempted correlations involving substituent parameters gave only positive ρ values. This shows normal substituent effects is operates in all the chalcones. The Chemical shifts observed for Hα protons in the present investigation are correlated well (r=990) with Hammett sigma constants. The other constants σ+, σI, and σR of this proton chemical shifts and Hβ were satisfactorily. The correlation with σR parameters is very poor in both the cases. This is due to these values are incapable of predicting chemical shifts individually due to the domination of cross conjugation between carbonyl group and methoxy group in naphthyl ring(II). The multiple correlations involving either σI and σR or F and R values for these ketones are satisfactory that in most cases the multiple correlations are successful through the equations (5-8). Some of the single parameter correlations are shown in Fig. 3 and 4.
Fig. 3.Plot of δH-α (ppm) of substituted styryl 6-methoxy-2-naphthyl ketones versus σ.
Fig. 4.Plot of δH-β (ppm) of substituted styryl 6-methoxy-2-naphthyl ketones versus σI.
13C NMR Spectra:
From 13C NMR spectra the observed 13C Chemical shifts of Cα and the Cβ carbons are presented in Table 1. The ethylenic carbons near the carbonyl group in Scheme 1 are termed as Cα and those next to Cα are termed as Cβ. These chemical shifts are correlated36 with various Hammett substituent constants. The statistical analysis results are presented in Table 2. There is a fair degree of correlation obtained for Cα and the Cβ carbon chemical shifts with Hammett σ and σ+ constants. The degree of transmission of electronic effects is found to be higher with Cα carbon (r=0.974) than Cβ carbon. The good linear fitness are shown in Fig. 5 and 6. Correlations of σI and σR constants with these carbon chemical shifts are failed. The resonance and inductive effects of substituents are not capable for predicting the substituent effects individually on the π system of all chalcones. Uniformly σI and σR parameters or F and R values are adequately explain the substituent effects in all chalcones are evidenced from the correlation Eqs. (9-12) are,
Fig. 5.Plot of δC-α (ppm) of substituted styryl 6-methoxy-2-naphthyl ketones versus σ+.
Fig. 6.Plot of δC-β (ppm) of substituted styryl 6-methoxy-2-naphthyl ketones versus σ.
This synthetic methodology is very efficient and selective protocol for crossed-aldol condensation of 6-methoxy-2-naphthyl ketones and aldehydes to produced high yield of 6-methoxy-2-naphthyl chalcones in the presence of a reusable and environmentally beginning catalyst silica-sulphuric acid. Operative simplicity, easy procedure, better yield including washing the mixture followed by evaporation of the solvent are another advantages of this method. In correlation analyses infrared spectral data, the σ constants produce a fair correlation with carbonyl absorption frequencies in both conformers of all chalcones. Nuclear magnetic resonance spectral data correlation, Hα chemical shifts were correlated with σ constants significant than Hβ. Other Hammett constants produce a fair correlation except σR constant. There is satisfactory correlation obtained in the correlation of Cα and Cβ chemical shifts with Hammett σ and σ+ substituent constants.