A New Aromaticity Probe—The Ring Stretching Vibration Raman Spectroscopy Frequency

Aromatic degree of molecule depends on its stability (energy), structure (geometry), chemical reactivity, and spectroscopic properties. However, the most investigations on aromaticity based on the calculations rather than the quantitative measurements. Thus, it is very necessary to find an experimental aromatic probe by one kind of vibration frequencies.Group theory analyzes molecular structure. The target molecules all have the A1g/A1' vibration normal mode, indicating they are Raman-active. The conjugation degree is up to the value of interactive forces between adjacent atoms. The force constant size of RSVRSF(A1 g/A1') suggest the force scale between adjacent atoms. Therefore, RSVRSF (A1g/A1') values of the target aromatic molecules must be related to the degree of aromatic.The calculations for the geometry optimization, the values of the frequency and Raman spectroscopy of aromatic molecules-LnHn (L=C?Si? Ge, n=3,5?8), Mn(M=N, P,As, n=3,5,6), BnHn2-, CnHn, Nn (n=5,6) and C6H6-nXn(n= 1,6)(X=F, Cl, Br) were conducted using calculation B3LYP/6-311+g(d, p) method within GaussianO9 process package. Meanwhile, NICS values of the researched series of molecules were calculated at the B3LYP-GIAO/6-311+g(d, p) level, as well as the correlations between the values of their RSVRSF and NICS values by Statistic Package for Social Science (SPSS).Aromaticity size of LnHn (L=C, Si, Ge, n=3,5 ? 8), Mn(M=N, P, As, n=3,5,6) and their RSVRSF (A1 g/A1') continuously reduces with the ring size increasing. The R2 changes of the used regression model for NICS(min) of LnHn (L=C, Si, Ge, n=3,5?8) and their RSVRSF (A1g/A1') are calculated as 0.999,0.937 and 0.898, respectively. Their Regression equation are y=0.006x2-0.00001x-4.390, y=-0.042x+3.768, y=-0.061x+1.023, respectively. The R2 changes of the used regression model for NICS(min) of Mn (M=N, P, As, n=3,5,6) and their RSVRSF (A1g/A1') are calculated as 0.981,0.833, 0.998, respectively. Their Regression equation are y=-0.034x+22.785, y=-0.028x-2.457, y=-0.033x-7.304, respectively. They can be concluded that there is a significant relation between aromaticity size of LnHn (L=C, Si, Ge, n=3,5-8), Mn (M=N, P, As, n=3,5,6) and their RSVRSF (A, g/A,').Aromaticity size of B5H52-, C5H5-, N 5- and their RSVRSF (A1') continuously incrase. The R2 changes of the used regression model for NICS(min) of B5H52-, C5H5-, N5- and their RSVRSF (A1') are calculated as 0.804. Their regression equation is y=-0.025x+12.808. Aromaticity size of B6H62-, C6H6-, N6- and their RSVRSF (A)g) increase first and then decrease. The R2 changes of the used regression model for NICS(min) of B6H62-, C6H6-, N6- and their RSVRSF (Aig) are calculated as 1.000. Their regression equation is y=-0.018x+7.464.Aromaticity size of C6H6-nXn(n=1,6)(X=F, Cl, Br) and their RSVRSF(A1g/A1') continuously reduces. The R2 changes of the used regression model for NICS(min) of C6H5X (X=F, Cl, Br) and their RSVRSF(A1') are calculated as 0.980. Their regression equation is y=-0.139x+130.686. The R2 changes of the used regression model for NlCS(min) of C6X6 (X=F, Cl, Br) and their RSVRSF(A,g) are calculated as 0.994. Their regression equation is y=-0.024x+18.073.In summary, Aromatic of conjugated cyclic molecules and their RSVRSF(Aig/A1') are significant relation. It is possible to test aromaticity degree of the aromatic target molecules via testing the RSVRSF(A1g/A1') value experimentally and quantitatively.