ICSSgen and ICSScsv are end of support. The basic functionalities have been combined into py.Aroma, a multi-functional tool for aromaticity analyses. Please check the homepage of py.Aroma for more information.

Contents

• 1. Statement of need
• 2. Install and usage
• 3. 2D-ICSS analyses of 1-methylazulene

1. Statement of need

2D isochemical shielding surface (2D-ICSS) maps, also known as 2D-NICS (nuclear independent chemical shift) maps, are useful tools for investigating the aromaticity of cyclic molecules. A large number of ghost atoms, in addition to the target molecules, must be included in the input file for 2D-ICSS calculations. After completing the calculations, the magnetic shielding tensors of all ghost atoms must be extracted from the output files. This process is a huge and tiresome task; therefore, we present ICSSgen and ICSScsv, two open-source, highly efficient, and user-friendly Python programs, to easily generate 2D-ICSS maps.

2. Install and usage

ICSSgen and ICSScsv could be download from GitHub. To install and run the programs, please refer to the user manuals.

3. 2D-ICSS analyses of 1-methylazulene

2D-ICSS analyses of 1-methylazulene would be discussed in this section. All files in this section could be download from here.

1-Methylazulene was optimized at ωB97X-D/6-31G(d) level of theory with Gaussian 16 B.01 package. The optimized azulene is located on XY plane (Figure 1). Two 2D-ICSS maps would be plotted on the XY plane with Z = 0 and Z = 1, in the range of X from -7 to 7 and Y from -6 6 Å. The input files were created by ICSSgen (Figure 2) and submitted to Gaussian calculations.

NMR (GIAO method) calculations were conducted at B3LYP/6-31+G(d) level of theory. The output files were then, processed with ICSScsv. The magnetic shielding tensors (isotropic and ZZ component) of ghost atoms were extracted to .csv files. 2D-ICSS maps were plotted with those date in .csv files by Origin (Figure 3). From these maps, the aromaticity of 1-methylazulene has been well proved by the negative shielding tensor values. Furthermore, the on-plane maps (Z = 1) show contribution from σ bonds, which sometimes annoying. The over-plane maps (Z = 1) well produced the contribution from π electrons.

In the updated version 3.1, ICSScsv can save the 2D-ICSS image as .png file automatically after processing the output file. Python external library numpy and matplotlib were imported to plot the image (Figure 4).