Theoretical Study On The Correlation Between The Aromaticity And The Ring Stretching Vibration Roman Spectroscopy For The Aromatic Molecule

The aromaticity concept has been continuously developed and deepened with the current development of Chemistry Science. The theoretical criteria for the determination of the aromaticity sizes have been continuously developed. Among all the criteria, the Nucleus-Independent Chemical Shifts (NICS) determination criterion has been well received. Unfortunately, there has not been a set of reliable and effective methods for the experimental determination of the aromaticity sizes.The research found that the ring aromatic organic molecules have highly symmetrical the Ring Stretching Vibration Roman Spectroscopic Frequency(RSVRSF), and the aromaticity of substances is related to their conjugation (that is the ring conjugation n and a bonds). This conjugation is also determined by the equal conjugation forces among the adjacent atoms in their aromatic molecules. Experimentally, these equal forces between adjacent atoms manifest RSVRSF(A1g/A1’) with high symmetry. Then, we can speculate that the aromaticity sizes of substances must be related to the highly symmetric RSVRSF of substances. It is possible to experimentally and quantitatively determine their aromaticity sizes by testing RSVRSF(A1g/A1’) values. In this study, the advantage of Quantum chemistry theory in molecular structure and molecular spectrum calculation was used. In order to offer a theoretical reference for seeking an effective method of determining the aromaticity sizes of substances, while the values of the NICS and RSVRSF(A1g/A1’) for three series of the aromaticity molecular were calculated, the structural characteristics and correlation between the NICS value and RSVRSF(A1g/A1’) value were explored for the three kinds of the aromaticity molecular.The calculations of the geometrical optimization, NICS and Roman Spectroscopy for the aromatic Molecules-LnHn (L=C, S, Ge, n3-8)、CnXn (X=F、Cl、Br, n=3,5～8)、Xn (X=N、P、As, n=3,5,6)-were performed using the Density Functional Theory B3LYP Method, as well as the correlations between the values of the RSVRSF and NICS by Excell03. The comparison research on the uniformity between the theoretical calculation values and experimental values of the RSVRSF were taking C6H6as an example.The result indicates that the relative errors are within1.9%between the theoretical calculation values and the experimental values of the C6H6RSVRSF. As to the three series aromatic molecules LnHn (L=C、Si、Ge, n=3～8)、CnXn (X=F、Cl、Br, n=3,5～8)、Xn (X=N、P、As, n=3,5,6), the values of aromaticity reduce with the n increasing, respectively. For CnXn, the aromaticity increase according to the replaced sequence from the atom F to Br. RSVRSF about three series molecules all decrease with the n increasing. RSVRSF about the CnXn, increase according to the replaced sequence from the atom F to Br. For the LnHn (L=C、Si、Ge, n=3～8), the correction coefficients between the NICS(min) and RSVRSF are0.87,0.94, and0.90, respectively. For the Xn (X=N、P, n=3,5,6), the correction coefficients between the NICS(min) and RSVRSF are0.98and0.83, respectively. For the Asn(n=3,5,6), the correction coefficient between the NICS(0.5) and RSVRSF is0.62.There are positive correlation between the theoretical calculated values NICS of the LnHn (L=C,S Ge,n=3～8). CnXn (X=F、Cl、Br, n=3,5～8)、 Xn (X=N、P、As, n=3,5,6)series aromatic molecules and their theoretical calculated values of the RSVRSF, i e, the higher the aromaticity, the higher their RSVRSF.