IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 6, Issue 4 Ver. III (Jul-Aug. 2014), PP 45-56 www.iosrjournals.org www.iosrjournals.org 45 | Page Effect of electronegative elements on the NMR chemical shift in some simple R-X organic compounds 2 Mahzia Yahia M. , 1 Jalali - Muhammad A. AL 1 Physics Department, Faculty of Science, Taif University, Taif, AL-Haweiah, , P. O. Box 888, Zip code 21974, Kingdom of Saudi Arabia 2 Physics Department, Faculty of Science, Damascus University, Damascus, Syrian Arab Republic. Abstract: Organic halides and other organic compounds that contain electronegative elements, have a strong chemical shift and a brilliant NMR spectrum will prevail. Relationship between 1 H, 13 C NMR chemical shift and Electronegativity in some simple R-X organic compounds (X=F, Cl, Br, I, O, H, ...R=CH 3 or CH 3 -CH 2 -) give nonlinear equation, as well as a power series equation appears between nuclear magnetogyric ratio, magnetic shielding constant and chemical shift, which are not included in the theoretical expressions. More investigations required to remove the discrepancy between the theoretical and the experimental results. Keywords: Electronegativity, chemical shift, shielding constant, magnetogyric ratio. I. Introduction Nuclear magnetic resonance, or NMR is a physical phenomenon was observed in 1945[1,2], which occurs when the nuclei of certain atoms, firstly, subject to nuclear Zeeman effect[3,4,5]will Precession with the Larmor frequency [6, 7]. Secondly, exposed to an oscillating electromagnetic field (radio waves), then if the radio wave frequency exactly matches the precession frequency, the resonance phenomenon will happen and this is the so-called nuclear magnetic resonance. However, experimentally, it has been noticed [8, 9, 10] that a nucleus may have a different resonant frequency for a given applied magnetic field in different chemical compounds, this difference in resonant frequency is called the chemical shift or sometimes fine structure. So that the shift is observed only for molecule compounds, and not for ions or free atoms, because of the differences in shielding of the nuclear magnetic moment when chemical environment is changed, where the electronic configuration of a molecule depends on the chemical binding [11]. Electron density shields the protons and the nucleus feels weaker magnetic field because of shielding, where a chemical shift decreases because of inner-shell electrons make a barrier decreases the nucleus attraction on the outer electrons, and deshielding is the opposite of shielding. The nucleus feels stronger magnetic field, and a chemical shift of a nucleus increases due to removal of electron density, magnetic induction, or other effects. Nevertheless, electron density depends on electronegativity of nearby atoms, where electronegativity is a chemical property describes the power of an atom to attract electrons towards itself [12, 13, 14, 15]. In addition, Sensitivity of NMR [16, 17, 18, 19,] is dependent on population distribution (Boltzmann distribution), applied field strength, the gyromagnetic or magnetogyric ratio of the nucleus of a particle or system which is the ratio of its moment to its spin momentum and abundance of spin in population. After that, anisotropic induced magnetic field effects (paramagnetic or diamagnetic local induced magnetic fields from circulating electrons where a nucleus feels with them) [20]. This paper will concentrate on the effect of the electronegativity and substituents of electronegative elements at the NMR chemical shift spectra in some hydrocarbon compounds, and the relationship between chemical shift, electronegativity and Magnetogyric ratio, which will support theoretical studies. II. Quantum Theoretical Background In quantum mechanical terms, the nuclear magnetic moment of a nucleus can align with an externally applied magnetic field of strength B ext in only 2I + 1 way, either parallel (spin +1/2) with notation 0  or opposing B ext (spin -1/2) with 1  . The quantum state of a two level system(TLS) are thus called a qubit, the qubit of two configuration system may be given by the point on the Bloch sphere representation which is well known in nuclear magnetic resonance [21,22,23],thus one qubit state can be written in the form: