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Interaction Between Molecule Fragments Unbound by Chemical Bonds Through the Space during NMR 1H Spectra Registration
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Abstract: While analyzing the peculiarities of NMR 1H spectra of different classes of organic compounds we suppose that under recording spectra conditions the intramolecular interactions between unbound fragments of molecule take place through the space. The existence of mentioned interactions leads to the observed changes in spectra compared with expected values of alkoxyl absorbtion in esters of aralkyl acids or acetals of aralkyl aldehydes. The schematic drawing of investigated molecule containing fragments "K-L-M" is represented in Figure. The arbitrary division into the fragments is in accordance with functional principle and depends upon the formulated aim. The aim is the investigation of NMR spectral parameters of the fragment "M" depending upon the structure of the fragment "K" and conversely. The absence of chemical bonds between atoms of the fragments "K" and "M" is an indispensable condition. Both fragments are bound by chemical bonds only with "medium" fragment "L", with its opposite sides. In the linear conformation I the interaction of unbound fragments "K" and "M" is absent. It is possible in the curved conformation II. The analysis of chemical shifts in NMR 1H spectra of the para-substituted propylbenzens by general formula: p-X-C6H4-CRR1CH2CH3 (where R,R1 = H,CH3) was made. The alkyl fragment influence on the phenyl ortho-protons absorption was shown earlier. The presence of the aryl fragment influence on the end methyl group was now first shown on the value of the basic spectral parameters - the chemical shifts of methyl protons (δСН3Н) in comparison with analogous data of corresponding alkanes. There were developed and validated specific criteria for identifying such effect. We make the overall conclusion about high probability of the reciprocal intramolecular interactions between unbound fragments of molecule in sec-butylbenzens and sec-butylphenols (R=H; R1=CH3) and especially in tert-amylbenzens and tert-amylphenols (R=R1=CH3). Due to abovementioned criterion of the presence or absence of intermolecular interaction between unbound fragments it is probable that the interaction between methyl group of propyl fragment and hydrogen atoms of aryl fragment does not exist or has small value in the investigated n-propylcontaining compounds p-X-C6H4-CH2CH2CH3 (Y=H or OH).
Keywords: NMR 1H spectra, para-substituted propylbenzens, basic spectral parameters, experimental differential parameters, virtual differential parameters, intramolecular interactions between unbound fragments of molecule.