Understanding Aromaticity. Experimental and computational studies
Computational organic chemistry DFT and ab-initio methods are used to study principle chemical properties and in conjunction to experiments. Wide range of subjects that are studied and some examples are given here. (a) The nature of aromaticity – one of the principle concepts in organic chemistry which is still not well understood. Within this topic studies of the effect of strain on aromaticity have been carried out, allowing better understanding of the factors governing the aromatic behavior. A new tool (NICS-scan) that assigns diamagnetic and paramagnetic ring currents to molecules was developed. This tool is used to study the nature of compounds and has proved to be useful for assigning any cyclic conjugation (even if not aromatic or antiaromatic). (b) Calculation of CD spectra of chiral compounds. This allows the assignment the absolute configuration of an enantiomer that was experimentally prepared by comparison of the experimental and the calculated CD spectra. In addition to collaborating with experimental chemists, a user friendly code which will allow non-professionals to determine the absolute configuration of an enantiomer and the %ee is being developed. (c) Macrocyclic aromatic compounds, including structural predictions and understanding of unique reactions that these macrocycles undergo are studied computationally. (d) Understanding the factors that govern C-H bond dissociation energies within a unified concept. See list of publication for additional topics. Experimental chemistry Most of the experimental work uses benzocyclobutenes in different directions. The Ni-mediated synthesis of the compounds was developed in the group and allows efficient preparation of different derivatives including bis(cyclobuta)benzenes and tris(cyclobuta)benzene. These compounds are prepared and studied as potential precursors for elusive intermediates (e.g., cyclic C6) and as monomers for the preparation of different highly conjugated polymers.
Read more about the Aroma package
Stanger, A.; Ashkenazi, N.; Shachter, A.; Bläser, D.; Stellberg, P. and Boese, R. “Nickel Mediated Cyclobutabenzenes Syntheses. Trans-7,8-Dibromocyclo- butabenzenes. Their One Pot Preparation, X-ray Structure and Diels Alder Reactions.”, J. Org. Chem., 1996, 61, 2549-2552.Stanger, A; Ashkenazi, N.; Boese, R.; Bläser, D. and Stellberg P. “Hexabromotricyclobutabenzene and Hexabromohexaradialene. Their Nickel Mediated One Pot Syntheses and Crystal Structures.”, Chem. Eur. J. 1997, 3, 208-211.
Stanger, A. “Strain Induced Bond Localization. The Heteroatom Case.”, J. Am. Chem. Soc. 1998, 120, 12034-12040.
Stanger A. “Nucleus Independent Chemical Shifts (NICS). Distance Dependence and Revised Criteria for Aromaticity and Antiaromaticity.”, J. Org. Chem., 2006, 71, 883-893.
Stanger, A. “Can Substituted Cyclopentadienes Become Aromatic or Antiaromatic?”, Chem. Eur. J. 2006, 12, 2745-2751.
Stanger, A. ” The Different Aromatic Characters of Some Localized Benzene derivatives.”, J. Phys. Chem. A. 2008, 112, 12849-12854.
Sason Shaik, Zhenhua Chen, Wei Wu, Amnon Stanger, David Danovich, and Philippe C. Hiberty “An Excursion from Normal to Inverted C-C Bonds Shows a Clear Demarcation between Covalent and Charge-Shift C-C Bonds”, ChemPysChem, 2009, 10, 2658-2669.
Stanger, A. ” What is…..Aromaticity. A Critique of the Aromaticity Concept – Can it Really be Defined?”, an invited feature article, Chem. Commun. , 2009, 1939-1947.
Stanger, A. “Using NICS-scan for quantitative determination of ring currents”, J. Org. Chem.2010, 75, 2281-2288.
NICS-scan (J. Org. Chem. 2006, 71, 883-893), the σ-only model (J. Org. Chem. 2010, 75, 2281-2288) and the NICS-XY-scan (Chem. Eur. J., 2014, 20, 5673-5688) are useful methods to determine the presence of diatropic and paratropic ring currents (aromaticity and antiaromaticity), local and global.
Aroma is a plugin package that has been written by Dr. Anuja Rahalkar (a post-doctoral fellow in my group) that automates these procedures for using with the Gaussian software package.
Using Aroma circumvents the need to manually build the appropriate input files and saves the user the difficulty of manually handling vast amounts of numerical data, making the use of the NICS-scan, the σ-only model and NICS-XY-scan easy and accessible.
Aroma 1.0 accepts standard Gaussian input, output or checkpoint files as input. It has also the possibility to accept a non-standard input file (see the manual).
It can automatically perform (on request) geometry optimization and a frequencies calculation.
It automatically generates an input NICS-scan file for user-defined rings (and bonds and atoms in the case of NICS-XY-scan) using a user-defined BQ range and step size (defaults are 0-3.9 Å and 0.1 Å, respectively), as well as σ-only input files, and subsequently runs the appropriate Gaussian jobs.
In addition to the standard Gaussian output files, Aroma generates text files that contain all the NICS-scan data, and, if NCS and/or σ-only model procedures are requested, also text files that contain the π-MOs contributions to each of the BQs’ chemical shifts and the NICS-scan results for the model.
These files can be read by standard software (such as MS-Excel, OriginLab) for the analyses.
Finally, a text file, containing the results of the analysis according to 3rd degree polynomial fit and the calculation of the chemical shift (NICS(1)p,ZZ value) for each of the rings is provided.
Aroma is available as the source code that needs Python interpreter and several other libraries or as a stand-alone binary version, for Linux, windows and Mac-OS.
The manual, including installation instructions, is available for download here.
To download a Linux-compatible and a Mac-compatible version (source and/or binary) click here.
To download a Windows 7-compatible version (source and/or binary) click here.
Post doc: Weizmann Postdoctoral Fellow, University of California at Berkeley 1986-1988
Ph.D: Technion, 1985