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IJC-B Vol.48B [2009] >
IJC-B Vol.48B(04) [April 2009] >


Title: Synthesis and NMR spectral study of some 5-aryl-3-methylcyclohex-2-enones and 5r-aryl-3t-cyano-3c-methylcyclohexanones
Authors: Kamatchi, S
Mohan, R T Sabapathy
Gomathi, R
Pandiarajan, K
Keywords: Cyclohex-2-enones
cyanocyclohexanones
1H NMR
13C NMR
conformation
Issue Date: Apr-2009
Publisher: CSIR
Abstract:  Eight 5-aryl-3-methylcyclohex-2-enones 2a-h (Ar = C6H5, p-ClC6H4, p-MeOC6H4, p-O2NC6H4, p-MeC6H4, p-FC6H4, p-Me2­NC6H4 or m-O2NC6H4) and seven 5r-aryl-3t-cyano-3c-methylcyclohexanones 3a-c and 3e-h (Ar = C6H5, p-ClC6H4, p-MeOC6H4, p-MeC6H4, p-FC6H4, p-Me2­NC6H4 or m-O2NC6H4) have been synthesized and characterised by 1H and 13C NMR spectra. For 2a (Ar = C6H5) SEFT and HMBC spectra have been recorded. For 2e (Ar = p-MeC6H4) HSQC and HMBC spectra have been recorded. For 3a (Ar = C6H­5) HOMOCOSY, NOESY, HSQC and SEFT spectra have been recorded. Analysis of these spectra suggests that cyclohex-2-enones adopt sofa conformation with one of the methylene protons at C-4 and C-6 anti to H-5 and the other methylene proton gauche to H-5. The effect of the phenyl and methyl groups on the chemical shifts of protons and carbons in cyclohexenone ring are discussed. The cyanocyclohexanones adopt chair conformation with axial orientation of cyano group and equatorial orientations of the methyl and phenyl groups. The probable values for the proton chemical shifts of the various protons in the cyclohexanone ring of cis-3-methyl-5-phenylcyclohexanone 6 have been computed from the observed proton chemical shifts of 3a and the known effects of axial cyano group. The possible values for the 13C chemical shifts of the cyclohexanone ring carbons in 6 have been computed from the 13C chemical shifts of cyclohexanone and known effects of phenyl and methyl groups. Comparison of these values with the chemical shifts of protons and carbons in 2a suggests that the double bond at C-2 influences the 1H chemical shifts by polarization, magnetic anisotropy and electronegativity effects and the 13C chemical shifts by polarization and electronegativity effects.
Page(s): 553-562
ISSN: 0376-4699
Source:IJC-B Vol.48B(04) [April 2009]

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