The Structure And The Change Of~1HNMR Chemical Shift Of Saturated Amine And Alcohol With Concentration

On the basis of the principle of electronegativity, the electronegativity of N or O atomis larger than C atom’s, the chemical shift of the H atom which attached to N or Oatom(active H) should be larger than the H atom’s that attached to C atom(-H).However, when we study the structure characteristic of saturated amine and alcoholthrough testing1HNMR chemical shift of active H and-H, the fact is on the contrary.How to explain this? We suppose that the2p orbit of N or O atom is interleaving withthe empty2p orbit of H atom, which makes the chemical bond–NH2or–OH havepâ†'p Ï€ coordination bond, not just one single bond. As a result, the density of theelectron cloud around H atom will increase, which makes the1HNMR chemical shiftdecrease. We simulated molecules by Gaussian09at6-31G(d, p) basis set. Quantumtheories of natural bond orbitals (NBO) method had been applied to analyze theelectron delocalization and demonstrate the bond above exists possibly. At the sametime, the chemical shift regulations of amine and alcohol are slightly different. Withthe concentration of alcohol increases, the chemical shift of active H increases.However, the amine’s does not. We also calculated the chemical shift of saturatedamine and alcohol, and the result showed that the chemical shift of these two kinds ofcompounds presented opposite regularity as the increasing of the number of molecules(simulated that the strength of hydrogen bond increased with the increasing of theconcentration).